ATMOSPHERIC CHEMISTRY CHEM 5151
Popular in Course
Popular in Chemistry
This 84 page Class Notes was uploaded by Guiseppe Bednar on Friday October 30, 2015. The Class Notes belongs to CHEM 5151 at University of Colorado at Boulder taught by Staff in Fall. Since its upload, it has received 195 views. For similar materials see /class/232188/chem-5151-university-of-colorado-at-boulder in Chemistry at University of Colorado at Boulder.
Reviews for ATMOSPHERIC CHEMISTRY
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 10/30/15
TemperanneLGC Atm Composition Big Picture I Table 11 Mixing ratios of gases in dry air Gab Mixing ratio moi11101 Nitrogen N2 078 Oxygen 0 021 Argon AI 00093 Carbon dioxide C02 365x105 Neon Ne 18x10396 Ozone 03 00110x10395 Helium He 52x10396 Methane CH4 1710396 Krypton Kr 11x10396 Hydrogen H2 500x109 Nitrous oxide N 20 320x109 0 Units of mixing ratio M01 fraction Volume fraction ppm lmolec in 106 ppb 1 molec in 109 ppt lmolec in 1012 ppmv ppbv pptv 0 a mass fraction 0 Q approximate mass fraction of Kr in air More 011 Units Pressurembar 1 nnnv I l l 10 10 1012 Ozone number density Ozone mixing ratio molecu e cm39s parts per million by volume Fig 1 2 Variation of atmospheric ozone concentration with altitude expressed as an absolute number density and as a mixing ratio From Stratospheric Ozone 1988 UK Stratospheric Ozone Research Group HMSO London 1988 Units change the View very signi cantly Lack of wrong units in your assignments or exams Will be considered a serious a mistake Example on Units Solve in class Dr Evil decides to poison humankind by spilling 100000 55 gallon drums of tetrachloromethane in Nevada MW 2 154 g mole391p 159 g cm393 1 gallon 3785 liters Assuming that all CCl4 evaporated and that it does not react With anything calculate its mixing ratio after it gets uniformly distributed through the entire atmosphere Did he accomplish his objective given that the present day CCl4 mixing ratio is roughly 100 ppt How many drums could one ll With all the CCl4 in the atmosphere Atm Composition Big Picture 11 TABLE 11 Atmospheric Gases W Average Molecular Mixing Gas Weight Ratio ppm Cycle Status Ar 39948 9340 Accumulation Ne 20179 18 No cycle during Earth s Kr 8380 11 history Xe 13130 009 N2 28013 780840 Biological and l r 02 32 209460 microbiological 39 CH4 16043 172 Biogenic and chemical 1 CO2 44010 355 Anthropogenic and biogenic CO 28010 012 NH Anthropogenic and chemical 006 SH H2 2016 058 Biogenic and chemical N20 44012 0311 Biogenic and chemical d S02 6406 1085 10 4 Anthropogenic biogenic chemical Quay621 y ate NH3 17 10quot4 103 Biogenic and chemical or ethbnum 1182 10 6102 Anthropogenic biogenic chemical O3 48 104 10 1 Chemical 30 1281 Zr able Physicochemical j 0 Strongly oxidizing atmosphere 0 Most atm chemistry deals With trace species Earth s Atmosphere in Perspective 0 All major planets except Pluto and Mercury and some large satellites Titan have atmospheres 0 Properties of atmospheres on neighboring Mars Venus and Earth are amazingly different 0 Earth is unique in Very high 02 content close to spontaneous combustion limit High H20 content Existence of graduate students and professors on the surface Comparison between Venus Mars and the Earth Characteristir Venus Earth Mars Total mass 1027 g 5 6 06 Radius km 6049 6371 3390 Atmospheric mass ratio 100 1 006 Distance from Sun 106 km 108 150 228 801er constant W 11172 2613 1367 589 Albedo 75 30 15 Cloud cover Wt 100 50 Variable Effective radiative C 739 18 A56 temperature Surface temperature C 427 15 753 Greenhouse warming C 466 33 3 N2 0 lt2 78 lt25 02 70 lt1 pplnv 21 lt025 102 239 8 0035 gt96 1120 range 0 1 x 10quot1 03 3 X 10 1 7 4 lt0001 02 fraction Cloud composition 150 ppmv H2304 lt 1 ppbv H2 0 Nil Dust H20 C03 The intensity of the solar radiation over a square meter of surface at a distance equal to that from the Sun to the planet s orbit From Graedcl and Crutzen 1995 300 thermos39phere Drawn to scale V Altitude km 2 iii 7 77 A Lower Atmosphere is Flat For most practical purposes lower atmosphere can be regarded as at Earth curvature only needs to be considered in very special cases Earth does drag a veil of gas with itself exosphere with the size of approximately 10000 km however it is extremely dilute For reference space shuttle 300 600 km above the Earth surface Atmospheric Structure noquot 10391 1 1o 102 1O 10 100 Thermosphelre l I I 90 Phys1cal bas1s for P I 80 K Mesopause varlatlon 2 7o Mesospher oamp Phys1cal bas1s for T 3 6 variation g 50 Stratopause 3 40 30 I 20 Tropopause 10 gt Troposphere 0 I l l l l l l l l l I l I l l l I l 100 200 300 Temperature K FIGURE 11 Typical variation of temperature with altitude at midlatitudes as a basis for the din39sions of the atmosphere into various regions Also shown is the variation of total pressure in Torr with altitude top scale base 10 logarithms where 1 standard 08 rag PampQ LY Wmmsx va AEFSA an vb Zwonmjd d NMN Dm mhpmmimnnignQ QAEF w n W AWEMUMFE on V5 CCANMMEP 960 p6 ww w 0 V 3 Cami amp A 3 oxrp 0ng 54an3 W m3ka M s 97m 309v pnm sc ll 1 N A m ltH 3 WW H W P g V b u w MN 3b 415mb m L 3amp1ch ag IBM k 5 AMBQL MRI36 L 8 48 34mg V a ii 4 1 J 39 veinrm xrly RT A I 393 I K S1 D FA ij LgV Ud u i RT J21quot L1Lz bi IVA 33L b S m da 139 is use vh ZLQ 32 97 g 96le H P W M3 3 2 P H 3 7 P2 O EH O 715 dyq d SEC u Whig w bin 1 C zH amp GRAW Altitude km f f I air density V or pressure MESOSPHERE so k r 7 z STRATOSPHERE V 2 1o I TROPOSPHERE 0 I I I I I I I 1077 1075 103 om 01 1 Denslly kgm3 Pressure atmospheres T Variation A 1368 First order approximation From FPampP Fig 19 Atmosphere is transparent only surface is heated Loss by convection re radiation Shape of atmospheric temperature pro le T Variation 0 In the absence of local heating T decreases With height 0 Exceptions Stratosphere Chapman Cycle 1930s 2 hv gt 20 O 02 M gt 03 heat 0 03 gt 202 03 hv gt O 02 heat Q what is heat at the molecular level Mesosphere absorption by N2 02 atoms Lecture 6 Spectroscopy and Photochemistry 11 Required Reading FP Chapter 3 Suggested Reading SP Chapter 3 Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez Outline of Lecture 0 The Sun as a radiation source Attenuation from the atmosphere Scattering by gases amp aerosols Absorption by gases BeerLamber law 0 Atmospheric photochemistry Calculation of photolysis rates Radiation uxes Radiation models Reminder of EM Spectrum TABLE 32 Typical Wavelengths Frequencies Wavenumbers and Energies of Various Regions of the Electromagnetic Spectrum Typical wavelength Typical range of Typical range of or range of Typical range of wavenumbers o energles Name wavelengths nm frequencies v s 391 cmTl kJ einsteinl Radiowave 108710l3 3 x 104 3 gtlt 10 106 01 103 10 8 Microwave 1077108 3 x 109 3 x 1010 011 10quot 2 10 3 Far infrared 1057107 3 gtlt 101073 x 1012 1 100 10 2 1 Near infrared 103 105 3 X 101273 X 10 102 104 17102 Visible 4 2 Red 700 43 x 10 14 x 10 17 x 10 Orange 620 48 x 1014 16 x 104 19 x raj Yellow 580 52 x 1014 17 x 104 21 x 10 Green 530 57 x 10 19 x 104 23 x 10f Blue 470 64 x 10 21 gtlt 104 25 x 10 Violet 420 71 x 1014 24 x 104 28 x 102 Near ultraviolet 400 200 75450 X 1014 25 5 X 104 30 60 X 102 Vacuum ultraviolet 200 50 15 60 X 1015 5 20 X 104 6024 x 102 X Ray 50701 06 300 x 1010 027100 gtlt 10 103 106 y Ray g 01 3 x 10398 2 108 gt 10 For kcal cinstein 1 divide by 4184 1 ca 4184 J Blackbody Radiation Linear Scale 6000 K Relative intensity Wavelength um Figure 36 The blackbody or Planckian radiation spec trum The intensity varies with wavelength in a smooth and relatively simple manner The shape and position of the spectrum depend on the temperature ln general the lower the temperature is the greater the wave length of the peak intensity and the lower the overall intensity of the radiation will be For an object at a temperature of 8000 K the intensity peaks at about 05 microns similar to sunlight Log Scale llllllll I Illllll lltlll l Wien s law 01 10 10 100 Wavelength um Figure 37 Blackbody radiation spectra as a function of temperature kelvin over the entire range of tempera tures relevant to environmental studies The values are displayed here on a log log graph so that both the wavelength and intensity scales are greatly compressed and cover many orders of magnitude From P R Gast Air Force Cambridge Research Laboratory McGraw Hill 1967 Appendix B of Revision of Chapter 22 of the Handbook of Geophysics and Space Environments Air Force Survey in Geophysics 199 Office of Aerospace Research USAF Redford Mass Template only From R P Turco Earth Under Siege From Air Pollution to Global Change Oxford UP 2002 Solar amp Earth Radiation Spectra s 39 235333 K Sun 1s a rad1atlon source w1th 39 39 an effective blackbody temperature of about 5800 K Earth receives circa 1368 r 77 Wm2 of energy from solar a 5mm 7 150111 zuunu radiation Wavelength Angstroms Froms NidkorodOV Figure 38 The relative spectra of sunlight and Earth s blackbodv radiation referred to as terrestrial radiation or Earthglow The spectral regions of the emissions are seen to be quite distinct with little overlap of spectra Inmmsnyrnannmrann Question are relative Sunlight vertical scales ok in 2 Earth radiation r1ght plot gt i 0 2 4 Wavelength um Solar Radiation Spectrum 11 2200 i i i i A 2000 Top of the atmosphere E 1800 2 5 r 1600 Scattered by the atmosphere 1400 g 1200 e At the ground a 2 0 V 1000 39 7 1 3 Absorbed by the atmosphere a 7 800 1 E 15 5 600 g E 400 1 200 10 O l l l I L L I 3 0 04 08 12 16 20 24 28 32 36 40 m 0 5 WW Wavelength um O i I 3 Visible Infrared Figure 35 Details otthe spectrumthatreachesthetop o 39 39 39 quot39 i 39 i w of the Earth39s atmosphere and penetrates to the sur 0 200 400 60 80 1000 1500 2 00 260 3 00 face The outer envelope is the full intensity of sunlight Wavelength nm that one WOUid encounter in space The inner curve iS FIGURE 312 Solar flux outside lhc atmosphch and at sea level respectively The emission of lower beeeeee the Bethe etmeeehere eeeeere some itit ii if i if of the radiation back to space particularly at short wavelengths The shaded region below the inner curve indicates those regions of the spectrum where atmo spheric water vapor carbon dioxide and ozone mol ecules absorb the sunlight further reducing its penetra 8012 S ectrum is tion The units of solar intensity are often expressed as p watts per meter squared per micron of wavelength w strongly modulated mZ pm From JN Howard J I F King and P R Gast Thermal Radiation Handbook of Geophysics New atmospherlc scattermg York Macmillan 1960 Chapter 16 p 15 and absorption From Turco Solar Radiation Spectrum III Figure 34 The basic spectrum of sunlight The inten sity of sunlight peaks in the visible part of the spectrum and decreases in the ultraviolet region at shorter wave lengths and in the infrared region at longer wave lengths Within the visible region the spectrum can be further subdivided into the primary colors of light blue green and red The visible region actually contains a continuous spectrum of colors ranging from deep red at one end to violet at the blue end a 396 C 2 E Wavelength um Ultraviolet Visible Nearinfrared spectrum spectrum spectrum From Turco Solar Radiation Spectrum IV Solar spectrum is strongly 1015 E 03 modulated by atmospheric 1014 absorptions 7 i 0 Remember that UV photons 7 1013 g l have most energy E E O2 absorbs extreme UV in 1012 g mesosphere O3 absorbs most UV 2 E in stratosphere g 10 g Chemistry of those regions L E partially driven by those 1010 absorptions E Only light with Lgt290 nm 109 I l Iii HHIHH penetratesintothelower 150 200 250 300 350 400 troposphere Wm Biomolecules have same bonds FIGURE 332 Calculated actinic uxes as a function of altitude for a solar zenith angle of 30 and a surface albedo of 03 From DeMore et al 1997 From FPampP e g CH bonds can break with UV absorption gt damage to life 0 Importance of protection provided by 03 layer Solar Radiation Spectrum vs altitude A 160 E V 140 D 8 t 120 3 J 10 100 J t 8 80 g Absorption g 60 by atomic and 5 9quot molecular a g 40 oxygen and nitrogen Absorption E 20 e by molecular Ozone lt oxygen absorption I I I I I I I I I l l 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Wavelength nm FIGURE 313 Approximate regions of maximum light absorption of solar radiation in the atmosphere by various atomic and molecular species as a function of altitude and wavelength with the sun overhead from Friedman 1960 Very high energy photons are depleted high up in the atmosphere Some photochemistry is possible in stratosphere but not in troposphere Only 9 gt 290 nm in trop Solar Zenith Angle u Aside form the altitude the path length through the T h atmosphere critically depends on the time of day and geographical location Path length can be calculated using the at atmosphere 399 L approximation for zenith angles under 80 Beyond that Earth curvature and atmospheric refraction start to matter Eanh S 01a 139 F 111 X FIGURE 314 De nition of solar zenith angle 9 at a point on the 15 1 0 earth s surface quotAir Massquot m A0tila1 pathlength w L sec Vertlcal pathlength h TABLE 35 Values of the Air Mass m at the Earth s Surface for Various Zenith Angles a Calculated from m sec 0 and b Corrected for Atmospheric Curvature and for Refraction I o I Solar Flux Photons cm2 s41 nmll Zenith angle 0 deg m sec 0 Air mass m 0 100 100 10 102 102 1 013 At large SZA very 20 106 10 little UVB radia ion reaches the 50 156 156 troposphere gt0 200 200 70 292 290 78 481 472 1 o 12 86 143 124 300 400 500 700 1000 W avelen gth n m Source Demerjian er IL 1980 Direct Attenuation of Radiation 39txm i From FPampP amp S Nidkorodov I 0 x e I t t t t t l Sg as W up I E radiation intensity eg F I 0 E radiation intensity above atmosphere V 10 39 m E air mass I E attenuation coefficient due to o l absorptlon by gases ag A i s fquot quot quot o quot 39 39 39 39 39 T 39z A l 1 t1 t scatterlng by gases sg g 1 PM 5 em l a scatterlng by partlcles sp 3 m 1 absorptlon by partlcles ap l amigh a scattering Rayleigh scattering 39 i M 4 tsp at A ts at x l O r I H quotWe ll quot333217 more 001 I l l l 7 I Deep UV N2 02 200 300 400 500 600 700 300 complex M1d UV amp V1s1ble 03 w i th n Near IR H20 l m FIGURE 115 Attenuation coef cients it or light scattering Infrared C02 H20 Others Rayleigh scattering and uhsorplinn OZUHL absorption by gases and tag lt1 039 fur scattering tmtl scattering plus absorption aerosol extinction by particles I rom Peterson 1971 1quotle Dcmcrjism rt m 980 Scattering by Gases Air molecules N2 02 Purely physical process not absorption 0 Approximation Blue zsg 1o44105 tn 12t4 Strongly increases as xi Figure 311 Light scattering by air molecules Accord ing to the Rayleigh scattering law blue light which has decreases shorter wavelengths than red light is scattered more h at k effectively by air molecules Hence the clearsky illumi Reason W y S y hated bythe sun takes on the blue colorOtc the scattered gm is blue during the day Scattering amp Absorption by Particles Particles can scatter and absorb radiation Scattering efficiency is very strong function of Figure 83 Scattering on radiation beam processes of refleclion A refraction Bll refraction and internal reflection C and clll39lraclion D For a given wavelength Visible 9 05 pm Particles 052 um are most ef cient scatterers 2 Ln 4 Ln 394 39JI L um um I I iIIIMI illllllini u Illllilli Will discuss in more ILLIJl ill 1 lil ll J39nlliclc J liLLiiJclri illml iFlngl E Ed Scaltwmg efficiency 0139 greenllghl ll gtmil3yallquldwaler sphere than unity because ol diiiruclmn Miamid lron39 Jr than L Ai39rrmspnonc frica39elnrzg milieugir Dimmm Furs jarr lJriugL 1413 Gas Absorption BeerLambert LaW I 1210 eXp 0LN Allows the calculation of the decay in intensity of a light beam due to absorption by the molecules in a medium De nitions FIGURE 311 Schematic diagram of experimental approach to 39 A Absorbance the BeeriLambert law also Optical depth 1 0395 absorption cross section Solve in class Show that in the small 2 cm molec absorption limit the relative change in light intensity is approximately equal to absorbence n E dens1ty of the absorber moleccm3 From FPampP amp S Nidkorodov L E absorption path length cm BeerLambert Law II Pitfalls Other units are frequently used to express absorbance for example A lnIDI S ch A lnIgI and a E extinction coef cient L mol391 cm l 0 absorption coef cient atm391 cm l C 2 density of the absorber mol L39l P 2 partial pressure atm Base 10 is used in most commercial spectrometers instead of the natural base Abase 10 10gIDI Abase e1n10 Physical interpretation of 0 039 absorption cross section cm2 molecule 7 Effective area of the molecule that photon needs to traverse in order to be absorbed 7 The larger the absorption cross section the easier it is to photoexcite the molecule 7 Eg pernitric acid HNO4 Light absorption Collisions c as 1045 cmzmoiec c as 1048 cmzmoiec me S N lmmde Measurement of Absorption Cross Sections Measurement of absorption cross sections is in principle trivial We need a light source such as a lamp UV a cell to contain the molecule of interest a spectral filter such as a monochromator and a detectorthat is sensitive and responds linearly to the frequency of radiation of interest Detector easurements are repeated for a number of concentrations at each wavelength of interest Although seemingly trivial in practice such measurements are dif cult because of impurities especially when it comes to very small cross sections lt 1020 cmZmolec an1lcm2 From S Nidkorodov Solve in class Sample contains 1 Torr of molecules of interest with c3x1041 cm2lmolec and 1 mTorr of impurity with cr2x1039l8 cm2lmolec What is the total absorbance in a 50 cm cell Example UV Attenuation by 03 and O2 Attenuation coefficient is dominated by 03 absorption in the 200300 nm window Therefore direct attenuation can be easily calculated from known absorption cross sections of 03 Similar formulas apply to attenuation by 02 in 120180 nm window 12 100m em W Where A 2 column density A l 032dz Alternatively written 12 100m N where r 2 optical depth r t z TUO DX mgtlt 032dz From s Nidkorodov Solve in class Using barometric law estimate column density of OZ in the atmosphere By how much does atmospheric OZ attenuate solar radiation at around 170 nm as 1047 cmzlmolec at noon m 1 Assume that 02 fraction 21 is independent of altitude and T 270 K Ans 4x10 by exp 107 Solar Radiation Intensity To calculate solar spectral distribution in any given volume of air at any given time and location one must know the following Solar spectral distribution outside the atmosphere Path length through the atmosphere Wavelength dependent attenuation by atmospheric molecules Amount of radiation indirectly scattered by the earth surface clouds aerosols and other volumes of air Scatte red 5 Y radiation Direct Volume SOIaT of radiation Reflected radiation Scattered reflected radiation Earth FIGURE 316 Different sources of radiation striking a volume of gas in the atmosphere These sources are direction radiation from the sun radiation scattered by gases and particles and radiation re ected from the earth s surface From FPampP Scattering by gases and pa ices Surface Albedo Albedle 2 Wavelength dependent Question for the same incident UV solar ux will you tan faster over snow or over a desert Re ected Radiationl Incident Radiationl TABLE 36 Some Typical Albedos for Various Types of Surfaces Type of surface Albedo Reference Snow 0169 Angle et 1 1992 093quot Dickerson et al 1982 09710 Junkermann 1994 Ocean 007b Dickerson et 01 1982 006 008 Eck et 11 1987 Forests 006 018 y Dickerson et 51 1982 002 Eck et 11 1987 017 Anglo et 11 1992 Fields and meadows 0037004 Eck et 11 1987 Desert 006 009 Eck et 11 1987 Salt ats 057 065 Eck at 11 1987 Minimum re ectivities at 370 nm b Measured With respect to N 02 photolysts From FPampP 10 Total vs Downwelling Radiation From Wameck FUI FD FTI FU I 20 F1 If atmosphere was Zlkm completely transparent 1O and surface completely 3325nm absorbing albedo O X20 X78 FU O 0 FU 39 FD FT39 39 Viv FD FT 1 20 Due to gas aerosol zkm scattering and surface 10 575nm re ection Xdoo FU can be large 0 015 1 1TB 05 1 FT gt SOlar FIGURE 210 Upward directed flux PU downward directed flux FD and total actinic ux F1 as a function of altitude in the lower atmosphere Values are given relative to a solar constant of unity for two wavelengths 3325 and 575 nm and for two zenith angles 20 and 78 The calculations of Peterson 1976 included Rayleigh scattering absorption by ozone and scattering and absorption by aerosol particles Calculation of Photolysis Rates I Generic reaction A hv gt B C M dt JiiA A firstorder process J 39 What does J A depend on JA depends on Light intensity from all directions Actinic ux Absorption cross section 039 Quantum yield for photodissociation g All are functions of wavelength ll Calculation of Photolysis Rates 11 Generic reaction A hv gt B C M dt 4M i aAltzgt AltzgtFltzgtdzx A J A rst order photolysis rate of A s1 0AM wavelength dependent cross section of A cm2 QM wavelength dependent quantum yield for photolysis F A spectral actiniclax density cm2s So what are the smallest cross sections that matter The solar actinic ux photons cm392 s391 nm39l is of order 1014 In many cases we need to know whetherthe photolytic lifetime of a molecule is 10 days J10396 st or 100 days J10397 4 This means that cross sections as small as 103920 cm2 or even smaller are potentially interesting Such small cross sections are very challenging to measure with sufficient accuracy Radiation Fluxes De nitions Quantity Description Units F Actinic ux density energy crossing a unit area per unit time without J m2 S1 consideration of direction we do not care where photons come from F 1 Spectral actinic nx density same as ux but per unit wavelength J m392 s391 nm391 E Irradiance same as ux but for a unit area with a xed orientation J m392 s391 E Spectral irradiance same as radiance but per unit wavelength range J m392 s391 nm391 L0 Q Radiance radiant ux density per unit solid angle J m392 s391 sr391 2 1 1 1 L0 q 1 Spectral radiance same as radiance but per unit wavelength range J m S nm sr 2 E JL6 cos 66in I L6 cos sin d dqp a 0 0 2 F JL6 da Huamsin 6d6d a 0 0 Radiance as a function of direction gives a complete description of the radiation eld When L is independent of direction the eld is called isotropic in which case E 7Z39L andF 27tL Solve in class There are 109 photons flying into a 0 01 cm diameter opening every second What is F with respect to this opening in units of lcm2s 12 Radiation Mesurements Flat Plate Irradiance Quartz grains Coaxual quartz tubes FIGURE 317 Typical device Eppley Laboratories Model 848 used to measure solar irradiance The detector consists of a differen tial thermopilc with the hot junction receivers blackened with at black coating and the cold junction receivers whitened with BaSOLt photo supplied courtesy of G L Kirk Eppley Laboratories Julikermann r 1 1989 Radiation does not just come directly from the sun scattered radiation is just as important Measure total or spectrallyresolved ux Use models Collimator Photomulliplier Inner dome Radiation shield Sm Interference filter 2n 12 0f Actinic Flux Outer dome FIGURE 320 Schematic diagram of a 2x radiometer used to measure aciinic uxes adapted from From FPampP Radiation Models Predict radiation intensity As ftime altitude latitude 7t Results of Madronich 1998 described in text Will use extensively in homeworks amp exams Typical model results From FPampP TABLE 37 Actinic Flux Values F A at the Earth s Surface as a Function of Wavelength Interval and Solar Zenith Angle within Speci c Wavelength Intervals for Best Estimate Surface Albedo Calculated by Madronich 1998 wavelength Solar zenith angle deg interval nm Exponent 0 10 20 30 40 50 60 70 78 86 Actinic uxes photons cm 2 s 1 290 292 14 000 000 000 000 000 000 000 000 000 000 292294 14 000 000 000 000 000 000 000 000 000 000 294 296 14 000 000 000 000 000 000 000 000 000 000 296 298 14 001 001 001 001 000 000 000 000 000 000 298 300 14 003 003 002 002 001 000 000 000 000 000 300 302 14 007 007 006 004 003 001 000 000 000 000 302 304 14 018 018 015 012 008 004 001 000 000 000 304 306 14 033 032 029 023 016 009 004 001 000 000 306308 14 051 049 045 037 028 017 008 002 000 000 308310 14 066 065 060 051 040 027 014 004 001 000 310312 14 099 097 090 079 064 045 025 009 002 000 312314 14 122 119 112 100 082 061 036 014 004 000 13 Example model results 8 5750 nm 6 4450 nm 4025 nm 4 3755 nm 3255 nm 3125 nm Actinic flux at the surface 1014 quanta cmquot2 5 1 nm 1 Solar zenith angle 6 degrees FIGURE 321 Calculated actinic ux centered on the indicated wavelengths at the earth s surface using best estimate albedos as a function of solar zenith angle from Madronich 1998 Summer solstice 20 30 Equinox Winter solstice Solar zenith angle 9 0 llll 9 4567891011121234 am Pacific Standard Time 5 6 7 8 pm FIGURE 323 Relation between solar zenith angle and time of day at Los Angeles California from Leighton 1961 From Q summerwinter solstices intensity at 445 nm 8 am noon Examples of Photolysis Rates 10291 1 5 2392 J 03 units of 10 s Amwbmm xmwemm l Time HST 14 A A 00 O N IlllllllllIlllllllllllll ll l J N02 units of 10393 3391 NONAm O o l r r 40 60 80 Solar zenith angle 0 FIGURE 330 Values of JNOZ at 7 to 75 km altitude as a function of solar zenith angle 6 measured using 2w radiometers circles compared to a model calculated photolysis rate solid line Adapted from VolzThomas et 11 1996 FIGURE 329 Measured rates of O3 photolysis 103 shown as heavy solid line at Mauna Loa Observatory on two days October 2 1991 and February 3 1992 compared to model calculations using two different assumptions shown by the lighter dotted and dashed lines respectively for the quantum yield for O3 photolysis at i gt 310 nm Adapted from Shetter et 1 1996 From PampP l4 Example Photolysis of CH3CHO CH3CHOhv gtCH3HCO a 42 J 2 zedM 2 AFAM aCHNCO b M W U W U TABLE 319 Calculated Photolysis Rate Constants for CHCHO Photolysis at 30 N Latitude Six Hours after Noon on July 1 Actinic ux Absorption cross Quantum yield for m section reactions 92 and 9b Wavelength 10 quot39nv quot interval photons lt10 2 cmz whom BF u DP AA nm cm zs l moleculequot 11gtm9quotx dx lfblk 1075 5 1 10quot 5quot 290292 0 4 78 052 001 0 0 2924294 0 4 51 050 0 0 U 294296 0 4 27 0 48 0 0 0 296298 0 4 33 046 0 0 0 298300 0 4 29 044 1 0 0 300302 0 401 0 42 0 0 0 302304 0 367 0 40 0 0 0 3044306 0 342 0 37 U 0 0 3061308 0 338 0 33 0 0 0 3950 3 0 001 313 U 27 0 0008 0 310 317 002 273 0 25 0 0013 0 312314 004 2 49 J 21 0 0020 0 314316 006 2 20 0 17 0 0022 0 3164118 010 201 014 0 0027 0 318320 013 185 011 0 0026 0 320 325 052 143 0 7 0 01050 0 325 330 096 0914 0 0017 0 002 Totalsquot EcpqunDFM 0183 X 10quot quot I carthisun correction distance 0139 0966 From FPampP Lecture 1 Introduction to Atmospheric Chemistry Required Reading FP Chapter I amp 2 Additional Reading SP Chapter I amp 2 Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez Outline of Lecture 1 Importance of atmospheric chemistry Atmospheric composition big picture units Atmospheric structure Pressure profile Temperature profile Spatial and temporal scales Air Pollution historical origin AP deaths Overview of problems smog acid rain stratospheric O3 climate change indoor pollution Continue in Lecture 2 Importance of Atmospheric Chemistry 0 Atmosphere is very thin and fragile Earth diameter 12740 km Earth mass 6 1024 kg Atmospheric mass 51 1018 kg 99 of atmospheric mass below 50 km Solve in class order of magnitude of mass of the oceans Mass of entire human population 0 Main driving forces to study Atm Chem are big practical problems Deaths from air pollution smog acid rain stratospheric ozone depletion climate change Structure of Course Introduction 0 Tools Atmospheric transport BT Kinetics ED amp Photochemistry Aerosols QZ Cloud and Fog chemistry 0 Problems Smog chemistry Acid rain chemistry Aerosol effects Stratospheric Ozone Climate change Interdisciplinarity of Atm Chem Very broad eld of both fundamental and applied nature 7 Reaction modeling gt chemical reaction dynamics and kinetics 7 Photochemistry gt atomic and molecular physics quantum mechanics 7 Aerosols gt surface chemistry material science colloids 7 Instrumentation gt analytical chemistry electronics optics 7 Air pollution gt toxicology organic chemistry biochemistry 7 Global modeling gt meteorology uid dynamics biogeochemistry 7 Global observations gt aeronautics space research 7 Air quality standards gt environmental policies and regulations Comparatively new eld 7 First dedicated text book written in 1961 by PA Leighton Photochemistry of Air Pollution 7 Ozone hole discovered in 1985 by British scientists and later by NASA 7 1995 Nobel prize awarded to Paul Crutzen Mario Molina Sherwood Rowland for predicting stratospheric ozone depletion Adapted from S Nidkorodov UCI Atm Composition Big Picture I Table 11 Mixing ratios of gases in dry air 0 Units of mixing ratio G Mixing ratio ab molmol 7 Mol fractlon Nitrogen N3 078 Volume fraction Oxygemoz 031 7 ppm 1 molec in 106 Argon Ar 00093 7 ppb 1 molec in 109 Carbon dioxide C01 365x105 7 ppt l molec in 1012 Neon Ne 18x10396 7 ppmv ppbv pptv Ozone 03 00110x10396 Helium He 5210396 Beware European bllhon 12 18 Mahamcm W106 10 trllhon 10 etc Krypt0uK139 1110396 i mass fraCtion Hydrogen H3 500x1039 Q approximate mass Nitrous oxide N20 330x10quot9 fraction 0f Kr in air From Jacob Atm Comp Unit Conversions TABLE 25 Conversion between Units of Concentration in ppm pphm F39pr ppt and Molecules cm 3 Assuming 1 atm Pressure and 25 C Molecules atoms or Parts per Unit radicals per cm3 mquot ippm 245 x 10 3 103 l pphm 246 X 10 10quot lppb 246 x in 10m 1 ppt 246 x 107 quot1 ppm in units of mass per cubic meter 409 X MW 14g 5 m 0 More complete tables on inside front cover of FPampP More on Units Pressurembar I I l n I l l 101 1011 1012 0 2 4 6 8 Ozone number density Ozone mixing ratio molecule cm39s parts per million by volume Fig 12 Variation of atmospheric ozone concentration with altitude expressed as an absolute number density and as a mixing ratio From Stratospheric Ozone 1988 UK Stratospheric Ozone Research Group HMSO London 1988 0 Units change the View very signi cantly Lack of wrong units in your assignments or exams will be considered a serious a mistake I Adapted from S Nidkorodov UCI Example on Units Solve in class Dr Evil decides to poison humankind by spilling 100000 55gallon drums of tetrachloromethane in Nevada MW 154 g mole3910 159 g cm393 1 gallon 3785 liters Assuming that all CCl4 evaporated and that it does not react with anything calculate its mixing ratio after it gets uniformly distributed through the entire atmosphere Did he accomplish his objective given that the present day CCl4 mixing ratio is roughly 100 ppt How many drums could one fill with all the CCl4 in the atmosphere Adapted from s Ntdkarodav UCI Atm Composition Big Picture 11 TABLE Almovphn inoum ampP Gas Wclgm Rana Plml Cycle Slams N 2x013 724mm Bmlogiml m I co 2mm 1 l2 mm Ammung and chmnml Lll lsm m I n Bmgcmc and chemiral 4 NO 10th n V L 48 I41 LIquot Chemical m was 51 W h 39 Strongly oxidizing atmosphere Most atm chemistry deals with trace species Earth s Atmosphere in Perspective I All major planets except How about other planets Pluto and Mercur and some large satellites Titan have atmospheres Properties of atmospheres 39 M mnpvrnsm Mmquot quotrmrs Arm and Um hum r W cm v on neighboring ars mmln a a um w a Venus and Bath are mm m m an zmm rm mlmim y w as Earth is unique in 7 Very high 02 content close to spontaneous combustion limit 7 High HZO content 7 Existence of graduate students and rofessors on the Surface p Slidefram Mdkarodav U01 1 mum vs V r x m 39 7 ua 3 nu mmn Flat For most practical Lower Atmosphere is mavmosphere very special cases Earth does drag a veil of gas with itself exosphere with the size of approx39 ately 10000 however it is extremely dilute For ref ence space shunle 300600 km above the Earth surfac e From S Nrdkarodav UCI Altitude km mesosphere 5 Atmospheric Structure I From FPampP mammal N we m a Questions 00 l K I I w immunee 1 7 Physmal ba51s for P I W mam variation m mmmriaaa 7 Phy51calba51s for T E w variation 3 5 3 w m 20 1 amaa m troposphere t a a a 2m we I I I l l l I ma anewm noun Ll Typical winner a Icmpcmlurc mm mam a midlamudn a 1 m luv m awayquot a me mmnsphcm inm wrlmu regmm Alw mwi a me lawman of uul paella km Ter m altitude mp scale has in iagaammu um l mam AS 11 Pressure Variation horizontal awn A piessnregradlem force PueruznA lrl 2 weight lugHz Flgurp 23 Vemcal forces acting on an elementary slab 039 atmosphere Write differential mass balance for slab Solution pzP0 e39ZH 999 of mass below stratopause AS 111 Species Variation HZ RTZMwajr g Dalton s law each component behaves as if it was alone in the atmosphere Hiz RTzMwi g 7 02 at lower altitudes than N2 7 Some scientists CFCs could not cause stratospheric O3 depletion too heavy to rise to stratosphere But gravitational separation due to molecular diffusion much slower than turbulent diffusion 7 Only gt 100 km enriched in lighter gases AS IV T Variation From FPampP Fg 19 First order approximation 7 Atmosphere is transparent only surface is heated 7 Loss by convection reradiation 7 Shape of atmospheric temperature profile AS V T Variation In the absence of local heating T decreases with height Exceptions Stratosphere Chapman Cycle 1930s 02 hv a 20 OOZM4gtO3 heat o 03 a 202 O3thgtOO2 heat 7 Q What is heat at the molecular level Mesosphere absorption by N2 02 atoms Temperature Inversions a b Normal positlve lapse rate Aluiude Negative lapse rate lnversion height Temperature FIGURE 218 Variation or temperature with altitude within the troposphere a normal lapse rale b change in lapse rate from positive Io negative elraraeterisric of a thermal inversion Invers1on layer temperature increases w1th height Supresses mixing Why Atmospheric Vertical Stability I Adiabatic Lapse Rate 1 7 vertical temperature pro le When air ascends or descends adiabatically ie Wo giving or receiving heat 7 For Earth F 98 Kkm391 7 Will deduce it from rst principles later in the course Buoyancy force Fb pg 7 pg Plt7p Plmmm FLUID Atmospheric Vertical Stability II adiabatic Actual A 39 Inversion Q which of the following pro les are stable and unstable 7 Stable a small perturbation is damped 7 Unstable a small perturbation is amplified Spatial Scales of Atm Chemistry TABLE 13 Spatial Scales of Atmospheric Chemical Phenomena me SM Length Scale km Phenomenon Urban air pollulion 17100 Regional air pollution 1 1000 Acid raindc 0 mon 100 2000 Toxic air pol ta Drl0 Stratospheric ozone depletion WOO 40000 Gr enhouse gas increas 1 00 40000 Aerosol climate Interact ns IOU 40000 Tropospherie transport and oxidalion processes 1 40000 Stratosphericrlropospheric exchange 0 1 100 Stratospheric transport and oxidation processes 140000 Enormous range of variation 7 Typically separate research communities don t talk much to each other Spatial and Temporal Scales lMicroscale 13527132 33135 Sm a iu iih From sap Tight link mquot 7 533 eggs between r i i C 1 390 spati a1 amp inlethemisphenc 1 yr 2 Mlxmg Tim temporal wed 3m Mlodelalely Lon l lmrahempheric i MW Time scales Temporal Scale 395 NO ldny a HIO Boundary Layer XDH MS Mixing Time quot LCnlix 7 77 lEonrhved peueiCH 0 g mo F H01 39 l moi on i x i i x i lm 10m lmm l m lukm mom Winn 10000er S anal Scale F FIGURE 117 51mm and wmpnmi mm mummy rm atmospheric constituents A avor about the main problems London smog 7 Primary pollutants Photochemical LA smog Global tropospheric pollution Particles 7 Health 7 Visibility Acid deposition Stratospheric ozone depletion Global climate change FIGURF mm Air Pollution amp Excess Deaths TABLE Ll Some IncidAIus I Exc Dim Amcima in Smog minim r vim Hm mm dulllx ii In mm M me rum unw mum um chkhc ms and Comm ii in Hwy Cold days strong inversions foggy Smoke Fog Smog llllllllllllll izsassiasiouizums Governments industry 0mm amp scientists start to 12 animmum in 50 mi quotmm is well 0 rm mIII during mi i952 smog cplmdt uduplcd mm wukm recognize Importance of AP From FP amp P M T Primary Pollutants Primary emitted directly e g Pb 7 You reduce emission to reduce concentrations Secondary formed in the atmosphere eg O3 Pb was easy 7 Almost all from gasoline vehicles 7 Added to gasoline as antiknock agent 7 Did Without it after regulation required its remov Many countries still use leaded gasoline 714 ofgasoline in Spain most in Africa Phothochemical LA Smog Sharp contrast to London sunny hot days Eye irritation plant damage Concentralion ppm Organics NOx sunlight 7gt 03 other products Now Widespread mew problem throughout FIGURE L3 Diurnal varianun of N0 N0 and Iolul oxidant m the world Pasadena Calimmm on July 25 73 aduplcd 1mm FinlaywnPnls im andFm 777 F39ameicP I n woo 15m 20m 25m 1950 s HaagenSmit What causes photochemical smog 0 Observation NO emitted first then forms N02 then 03 peaking in afternoon Can Chapman mechanism produce 03 in LA Requires 02 hv gt 20 Needs hard UV that does not reach surface Need another route Blacet 1952 photodissociation of NO2 N02hv7clt430nm gtNOO o 02 M gt 03 Also NO 03 gt N02 02 rapid What causes smog II 0 How does NO form N02 Wo O3 0 Thermal reaction 2N0 02 gt 2N02 very slow 0 Answer organic oxidation RCHZR OH gt RC39HR H20 RCHR 02 RICHR peroxy radical 00 RICHR NO gt RICHR NO2 alkoxy radical 00 0 Every step in organic oxidation creates N02 then 03 Lecture 12 Gas Phase Organic NOX UV Reactions Reguired Reading FPampP Chapter 6 Additional Reading SampP Chapter 5 CatchingUp Reading Jacob Chapters 11 amp I2 aree online Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez Outline of Lecture The big picture of atmospheric oxidation A OXidants B Lifetimes of Organics Today C Reactions of Alkanes D of R R0 and R02 Radicals E of Alkenes amp Biogenics F of Aromatics G of OContaining Organics H of N Containing Organics 1 Chemistry of Remote Regions J Atm Chem amp Biomass Burning We won t cover everything in class read the rest in the book 7 Have to know how to nd interpret quickly TABLE 26 Typical Boundary Layer N0r Emissions of NOX Region Nox PPb Urban suburban 10 1000 NOx NO NO2 Rural 02 10 Remote tro ical forest 002 008 P NO N O N 02 H N 03 Remote marine 002004 CH3COOONO2 HONO No3 N205 AlkylONO2 Soume National Research Council 1991 TMJLE 11quot Estlmllui Global Emhhmsofhll Typiclllofllw List W Mamilude Sources of NOX are mainly Sources inth 391 Conmrnu Fossil fuel Il nlblnll ai 21 Surl39acnmrce 3 91 NH anthropogenlc ega dlesel englnes Enil release natural and I1 Continental surfacemmu unLl39u39IIitl39IuEenici Most of NOX is emitted as NO Biemmhummi i Imusurrm mum Lightning 5 Free tropospheric smutr Lightning is an important natural source HWWM39W 3 Tmmnmm Aircraft El lIiil2 km matte 515 NH Tnnsport Ilrom stratosphere Ill 06 total N0 Fret tropospheric mum 295 Emma FCC I39m9n A rquot 39 ON 263 z V N Fuel Combustion x z 23 0 North America I Electrical Utility One oad Vehicles 0 g 280 30 Z 6 g 197 g From FPampP a 0 154 USSR quot5 amp Nizkorodov 39 o 39 LIELg 13 1 quotquotquot39T quot Europe v 39 39 39 39 39 2 93 7 quot 39Asia All Other 5 69 I I I I I I I I I I I I I I I Fuel Combustion Oiher 5 1 970 1 975 1 980 1985 Fuel Combustion Year Industrial FIGURE 23 NOX emissions in million tons of equivalent NO2 for the period 1970 to 1986 for Asia Europe North America and the FIGURE 2392 contribution of various sources m tom ammo USSR from Hameed and Dignon 1992 pogenc N0 emissions in the United States in 1996 from EPA 1999 YO yiliLttiis Emissions of VOCs Partially oxidized hydrocarbons VOC do quotat inCIUde On global scale biogenic emissions of VOC Methane Chlorofluorocarbons dommate o CO and CO2 Anthropogenic em1ss1ons account for 1020 of the TABLE 211 Median Mixing Ratio of the 25 MoslAhundant tOtal bU t they are very Important 1n urban areas Noumethane Organic Compounds Measured in the Summer 1987 Southern California Air Quality Study Where domlnate Median Mixing Ratio in pm Wmmmfcmmu Atmosphere contains over 600 documented VOC Ethane 271 Ethene 223 Acetylene 173 TABLE 210 Estimated Global Anthropogenic Emissmns of PmlJane 56390 Nonmethane Volatile Organic Compounds Propane 7 8 39 39 Emission T yrquot iButane 194 ActIVIty g Butane 420 iPemane 524 FUEL PRODUCUONJDISTRIBUTION Pemane 24 0 Petroleum 8 ZMethylpcmane 160 Natural gas 2 B Me39hylpemne Oil re ning 5 Hexane 39 39 25 Memytcyclopemane 10 1 Gasoline distribution Benzene FUEL CONSUMPTION 3 Methylhcxane 39 35 Heptane 60 25 Methylcyclohexane 70 I I 491 Crop reSIdues including waste l45 Toluene Eihylbenzene 76 Charcoal 25 m andpXylenes 252 Dung cakes 3 onylene 100 From FPampP Road transport 36 l24Trimethylbenzene 3 2 amp N k d Chemical indus ry 2 Fomaldehyde 9 1 H OH 0V Solvent use 20 Ace aldEhyde 8 Uncontrolled waste burning 3 Acetone 224 10 quotPans per billion of carbon ppr is the parts per billion of carbon atoms in the OTHER molecule II is simply the volume mixing ratio of the compound muitiplied by the Total 142 number of carbon atoms in the molecule Source Lurmann and Main 199 Sam Middlemn 0995 Atmospheric Regimes Urban Remote Straws here Troposphere Troposphere p N Ox levels High Low Low Organics Petrochemical Biogenic None UV ux Low Low High P 1 atm 1 atm to low Very Low T warm warm to low low to warm Very different conditions in the different regions regimes Different set of reactions are important Why chemistry of these regions is often considered separately The Big Picture I 0 Organics NOx UV gt 03 oxidants particles 0 The details are complex Next three lectures 2 on organics one on NOX Organics E g hydrocarbons like gasoline vapor octane C8H18 Burn rapidly at high temperature 2000 K in an oxidizing atmosphere C8H18 125 02 gt 8 CO2 9 H20 pollutants Burn slowly at low temperature The Earth s 39 c is a low Organics end up mostly as CO2 H20 Not perfectly clean ame intermediates and side products are pollutants ame The atmosphere as a low T ame Reaction rates of as fT for CH4 OH gt CH3 H20 k 265 x 103912 e480 cm3 moleC391 s1 CH4 OH Reaction Rate CH4 OH Reaction Rate 1E11 1E12 1E13 1E14 1E15 l 250 1000 1750 2500 250 1000 1750 2500 T K T K Rate cm3 melee1 s A on rn rn a a l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l Rate cm3 molec1 s1 What are the relative lifetimes of CH4 at ame VS ambient temperatures Does this make sense Answer Radical Concentrations Lifetimes ofCH4 Salgz saeiini in atmosphere a few years 1 N I ina ameafew us l Ratio 1013H We can t explain that with the reaction rate Ratio 103 Key are radical concentrations 0 Atmosphere 01 ppt 0 Flame 1 ppth Mole fraction OH quotI 1 0 12 L4 Ratio 1010 Excess Air Z Excess Fuel From Heywood 1988 Internal Combustion Engine Fundamentals I FuelAlf FuelA1rst01ch How do we proceed C8H18 125 02 gt 8 CO2 9 H20 is an overall reaction Many steps but very fast in ame In atmosphere very slow motion so intermediate steps quot HC CCC CC products are of great interest We will follow the C C chemistry of various H H H H H H H H organic groups H H A nightmare of quot HHgtL clltHH details for all species HCCOH H c H H C T Ethanol H HHCu MTBE H A I Radicals Radical 6H 66 species With an 39 u 39 u 39 39 39 unpaired H02 Cl electron ngh energy N z high tendency u u u to pair the electron to NO2 NO reduce the free u quot energy 3991R Often rapid R0 R02 reactions From Paul Ziemann The Oxidants 0 OH 7 Fast rates very low concentrations Somumbson 7 Habstraction CH4 OH gt CH3 H20 Lone I Attacks most organics O3 7 Mostly during the day O 03 7 Slower rates but high concentrations 0 O 7 Avid for electrons 7 Attacks double bonds CC 7 Day amp night N03 7 Fast photolysis during day important at nigl 7 Count Dracula H02 amp C1 kene Oxidant Sources in Trosposphere I Hydroxyl Radical 0H Hydroperoxyl Radical H02 39 PhotodiSSOCiatiOH 0f 03 Photodissociation of CHZO 03 l M gt 02 l GOD CHZO hv gt H HCO OCD HZo cm HO M HO M gt Photod1ssoc1at1on of 2 2 HONO and H202 HCO 02 gt H02 CO HONO hv gt OH NO H202 hv gt OH 0H From alkoxy radical Alkene oxidation feaCtiOnS RICHCHRZ 03 gt OH RCHZO 02 gt RCHO Ho2 pmd39 7 Byproduct of oxidation of 39 From HOT organics 7 NO H02 gt N02 OH A Sources of HOX OH H02 in Mexico City HOX drive smog and secondary aerosol chemistry HONO photolyzes at long A very important in early morning HCHO formaldehyde is dominant source 03 source needs to wait for O3 to be produced depends 7 0n the HONO HCHO Ozone OLE GIyCCHO 2 8 14 49 30 5 04 E 10 sum f f HON0 hu HCHO hv f l xxxN 03 hu 7 I 7 i a 03 alkanes r i xquot Glyoxal hv 7CCHO hv l I 0 E 1 2 1 8 24 From R VolkamerampW Brune MIT ampPSU Time Of day hours A O l D HOX production 0 8 A Oxidant Sources in Trosposphere II Ozone 03 Chlorine Cl Photodissociation of NO2 Seasalt chemistry N02 hv gt NO 0 N205g NaCls gt ClNOzg 0 02 M gt 03 M t NaN03s Nitrate Radical N03 010N02ggt NaCKS gt Mg NaNO3s Oxidation of NO2 ClNo2 hv gt C1 N02 N02 03 gt N03 02 12 hv gt 11 c1 Organic Compound Classes Hydrocarbons only C and H Alkanes decane AlkenesMonoterpenes Aromatics apinene toluene Mostly Mostly Biogenic Anthropogenic Organic Functional Groups FG atom or group of atoms with speci c structure and reactivity I i r 39rAlkane C rAldehyde CH C 39 t r Alkene C 39r Ketone cCR l 0 r Ether cOCL r Carboxylic acid clLOH l I r Alcohol CoH r Ester gRom l I httpWWW uwec educarneymjAdobe20handoutsNomenclature pdf nice page for catcthing up on organic nomenclature Lifetimes of Organics As always enormous number of possibilities but what is important Org X gt Products X is an oxidant dOrgdt kXOrg lifetime I lk X TAle 51 Eurmed Lifetimes or Rupmscnmllvc Organic in Ihu Troposphem on a vs no c u x rm39J unoppw isoppn 2x l rmquot8m l u x w cm h iiiv 39 v m unmsphum Immm x much longer V a u m A tCl 7 run 3 x ur cm moleculequot xquot mm A 31 x 10quotquot cmquot muncult v 7 tkiimm m 1 mam 7 and r 7 A mu M squot muw4 m x m C mom l mu n I J me Fm k 23 x llquotquotm Ram Com Tcmpunlurc mm 1m mnkcl quot s 41 xx Alkanes OH a 139 OH has strong tendency to gagm abstract H 3 2w u RHOH7gtRHZO 7 We will focus on R soon Wm Wilmimv Rate increases With Size and lm uhwmc m complexity 39l39flll lETCSEL 1 w 7 Mammurn rate lnmcmylpmmc My mumuiyumm m um CH4 is far slower than others 133 7 Focus on NonMethane quotD liq Hydrocarbons N MHC for urban ii smog 23034 5 lulu 7 Why CH4 survives and builds up to g be a greenhouse gas Mmmhm Ii m Alkanes Cl TABLE 54 RateCons Cl also likes to abstract H of Cl Ammswi RH C1 gt R HCl 10 CIII3 Also forms an alkyl rad1cal Alkane muleculequot 5quot Reactions compared with Mc hanc 0010 Elh us 59 collis1on rate Propane 137 n Butane 218 Importance VS OH lsuhutane 143 39 n Pentane 28 chemistry mHexanc 34 n Heptane 39 n Octane 46 n Nonane 48 rxDccane 55 From Alkinson 1997a temp k Ac r RT pm PM Fates of alkyl radicals R Radical nomenclature 7 Alkyl R 7 Alkylperoxide ROO or R02 7 Alkoxy RO or R0 R from oxidation of alkanes 7 Generated with all oxidants 7 Fate is similar for Habstraction radicals from other organics Only fate is reaction with O2 ROzM gtROZM k l X 103911 cm3 molec391 s391 7 Lifetime of R at ground level Alkylperoxy Radicals ROZ I React mainly with NO H023 mm as anagram inndo11No Ramon a m an R023 and N03 7 R02 NO 7 quot arm 7 Fast k 7 8 X 103912 cm3 molec1 5391 my smm name 7 Do not vary much With R m0 7 Products m Mainly 7 RO NOZ W 7 Again this is how we make 03 in m the troposphere n is Also 7 RONO2 alkyl nitrate m 7 Yields increase with R02 size g CH3OZ NO3 7 CH3O M No2 02 22321 w 7 Fast k 7 2 X 10 impOItant Hi ht itSI g Alkylperoxy Radicals R02 11 ROZ HOZ 7 ROOH 02 24a 7gt Carbonyl HZO 02 24b a ROH 03 240 7 ROOH is hydroperoxide ROOH 7 Mostly by 24a for small R other channels contribute for larger R 7 k 7 6 x 10 2 cm3 molecquot squot roomT ROZ ROZ 7 2RO 02 25a a ROH RCHO 02 25b a ROOR 02 25c TABLE 66 RNommmdnl Ram Cmumnu mi Branching Ruins a Room Tcmmarum or hs sou Rucnons mi so not mania rmm rem Ennmin mum is tzsai ist 42er R0 lcm moundquot rt izm w norr Run a 0 moon r 0 m u 37 s nr H u it 3 015 4167 Minor u 70 tins wlIJD 0H 1 umquot lt mm uociizciilo 13 x w 010 kill an n hb x m quot mm 4 my lUZ39 uus39 Relative Importance of R02 Reactions RO Products 2 R02 O R0 H02 N02 Critical parameter is the ratio of the corresponding reaction rates k CH3O2 NO z 77gtlt103912 cm3 molec13391 298 K k CH3O2 H02 z 56gtlt1013 cm3 molec13391 298 K k CH3O2 CH3OZ z 47gtlt1013 cm3 molec1 s1 298 K NOurban z 20 ppb 5gtlt1011 molec cm3 H02urban z CH3OZurban z 40 ppt 109 molec cm3 RateCH3O2 NO RatesRO2 CH3OZurban z 4000 NOclean z 1 ppt z 2gtlt107 molec cm3 H02Clean z CH3OZclean z 5 ppt z 108 molec cm3 RateCH3O2 NO RatesRO2 CH3OZclean z 1 Conclusion In urban atmosphere reaction with NO dominates high NOX limit In remote troposphere both pathways are similar D Alkoxy Radlcals R0 Three main fates Intramolecular Reaction with 02 Isomerlzation H 39oquot i C 02 CH 39 IZH CH3 39o HOZgt ozclt 27 3 1 1 2 IDH CH3 cli CH2 CH2 CHCH3 29 Decomposition H b 0 Where isomerization is CH3CCH2CH3 agt CH3 CCH2CH3 l H posmble 1t dommates H 28 lb T as R size inscreases O CH3Clt CHZCHS OtherWISe R0 02 H ham 5 Nllkumduv D Summary of R R02 R0 Reactions RCH3 OH gt RCH H20 02 M minor RCHZONO2 NO Ho RCHzo r RCHZOOH o2 HCH20 No2 I major R 02 02 Producis RCHO H0239 Decomposinon Isomerlzation FIGURE 62 Summary of alkanc oxidation by OH in airi me PM Oxidation of CH4 High NOX Case WW k298 K 10gtlt1Cr13 cm3ls cum 106 lcm3 row kCquot 32 years Ho2 C Followed by NO hv 02 gt NOO3 39 HCI xi 02 NO CH4 CH3 CH302 CH30 M No2 HO H20 2 k 245x1039 94775 CH O k298 K 63x103915 cm3fls 2 0mm 106 lcm3 WV row k OHquot 5years 0 0 HOZ 2 HCO H 2 Ho2 CO or M H2CO Oxidation of CH4 Low NOX Case O O CH302 CHgoH CHZO 02 CH4 CH3 2 CH302 or 39 H2 M CH30 CH30 02 Ho2 CHZO HZO 02 02 or CHSO CHZO CHgooH 02 H02 We already know what happens to CHZO it is converted to H2 H02 and CO How about CH3OOH and CH30H H20 OH HZO OH droplets CHSOZ droplets H2O CHgo H20 hv OH CHgooH CH30OH CH30H W CH20H 2 02 Ho2 o H20 CHZOOH CHZO OH CHZO FromS NIZkorodoV Big Picture of Organic Oxidation parent primary 1 generation 2quotd generation species products products VOCoxidant VOCoxidant I 39 39 chemistry chemistry I I I I I I I I I I I V I I CO2 I I I I J Aumont Lavai and Madromch accepted mACPD 2004 Fully Explicit Chemistry 1E07 1E06 1E05 1E04 1E03 1E02 nalkanes ialkanzs 1alkenes isoprene 3 4 5 6 7 8 Number of carbons 9 Complexity is enormous but starting to be tackled directly mlxing ram ppr g Hm m l l MM mmh CARBON BUDGET Fully explicit chemistry of nheptane m m m CPD 2mm Lecture 2 Introduction to Atmospheric Chemistry Part 11 Required Reading FP Chapter I amp 2 Additional Reading SP Chapter I amp 2 Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez A avor about the main problems Global tropospheric pollution Stratospheric ozone depletion Acid deposition Particles Health Visibility Global climate change Background 03 Concentrations 002 001 W n I I I x V850 1975 won 925 i950 1975 2000 Ozone ppm Yeav FIGURE L6 Typical trupospheric my cuneumn uiom in the 180039s and pracnl values Adapted lmm Valz and Kley I958 Tropospheric O3 7 Bad ozone effects on humans plants materials Roughly same chemistry as LA smog Globally increasing trend 7 Thought to be due to shift in chemical regime as NOx has increased Stratospheric Ozone From FPampP v v v v 300 9quot myquot Stratospheric 03 w r n 39 S 250 V quotv 7 Good ozone nothing v W v to be damaged up there 200 39v39 protects us from hard 9 vv39 UV radiation 5 150 39 c v P I 100 I l 1950 1960 1970 1930 1990 2 0 Year FIGURE 7 Average total column ozone measured in 0mm at Halley Bay Antaruica from 1957 m 1994 adaplzd rmm Jones and Shunklin 1995 Discovered from ground measurements even though there were satellite measurements ctnhex 7s TOMS Total Ozone Monthly Averages ctnhex an ctnhex a at ctnhex 32 nhex 33 Chemical Origin of 03 Hole After 03 hole discovery 7 Many th dynamics chemistry Chemical measurements proved involvement of chlorine chemistry Predicted Rowlen 1974 7 Nobel Prize 1995 izu eories mixing 084 E 3 9 u 043 by Molina Lzmuda s From FPampP Ozann ppm inm of In chlnrmc nmnnxxm 7 Many unexpected noun LB Mcmumnl cummm 39 mr admll Clo u 39II M U numdr md UNI detalls un Aung 3 1mm pltd num Andan me unwxmmrmnc Status of 03 Hole mmch mummy s mums m 1m 1596 law Stabilized due to human action 7 Control and elimination of CFCs Not a hot research problem now still many interesting questions Frgxfram S Mdkarodav UCI pH ofrain decreases mostly due to HZSO4 Dire effects if soil cannot neutralize acids Health Effects of Particles I w Nasnphzrynx Nasaunrpharyngmllryugzal mm rummals s 03an n M 5 g a quot l39mcrlnahmndlmlmgmn Vestlbule I 9 Eplglnnls u Larynx l Pumunury Mm uu Termlnnl anmlula 0001 um nl w w Pinclzalammcrttlm new 2 Culculmm mm of mutual maul two at u Ilmg M Alveolar Dun ulyuupms mm 442 r s m lule u A mum mm m u l lwm Submicron and ultrafine Aw l FIGURE 2x schemach dlngmm a human respiralm um part penetrate most lme Hlmls w L Animal WWW Cumngm 1 1952 Ian wiltv u Suns Inc mgrmm by mmmm ul luhn Wllcv at Sam deeply Health Effects of Particles II Sulfale lug m Harvard Six39 15 I I ll 1390 1392 14 city study g 1993 if 13 8 Mortality a 1392 increases With E L H fine article w a 11 W concentration g 1 0 PT Disputed for a x g I decade now m 5 10 15 20 25 30 5 considered PMZS 9 m3 IGURE 214 Estimaled adjusted mon39 lily rate ratios taking me least polluted city Portage Wisconsm P as LEI TTopeka Mechanism still Kansas w ale own Massachusetts L St Louis Missouri H arriman Tennessee 5 Stcubcnville Ohio Adapted from uncertam Dockery et al 1993 Visibility Degradation I Particles can scatter From Jacob and absorb radiation r 0 These effect limit L atmospheric quot er refraction and Internal reflection to and dl raclion to SOLAR RADIATION 4 object 1 2 E background 3 Figure 85 Reduction of visibility by aerosols The visibility of an object is determined by its contrast with the background 2 vs 3 This contrast is reduced by aerosol scattering of solar radiation into the line of sight 1 and by scattering of 4 mlr rtrnn radiation from the object out of the line of sigh Visibility Degradation II Scattering ef ciency is very strong function of particle size 7 For a given wavelength Visible 7 05 um 4 Partlcles 052 um are 5 From Jacob most ef cient scatterers I5 I 115 I I I rl llvlll nl I In lllll immut ll1lllL lL ll l FigureaA Scallenng emciency algrsenlrghl r n imnl by a Inqu walersphara u mm than unlly because at dl ractlon Adapted lrom Jacobson m z rmd menmr s or I lmmspnmrc Alodslvmj Cambridge Llnwirstty Press Cambridge was Earth s Radiation Balance b mmmwn Soiav a inmm F39am FPampP I Climate WWW average weather NW m it I Driven by solar NEW radiation 2 entrainment 215 Depends on complex balance immmim we at of many terms we 1 gm 5mm mm Anl mmgnm Current small W E m perturbations in gas absorption causing heating Absamlwnm Mam quot20591019quot Lilcnma39 mmsiesai mph 4m Mi new by mm m Eannmsnum m wquot new i in mm Greenhouse gas concentrations cARauNniume 3 7 name w 3 we 3 HM 12W 7 39 39 3 him 7 o 1 an e i h mm WW quotmm mm m i i in i350 mat itsr 20 H mm inw 3 quotmums uxlnE 5 amt E z z 9 v i e gt ii i 1w amp 2 2 w 5 ii 8 9 3 E i n innii iMii NEH Wm I KYVH r in mm will itt vli Watt 13 0 mm mu Figure 71 Rise in the concentrations of greenhouse gases since the 18m eentu Earth s Temperature History Surface T as surrogate of climate WW m r Very large changes in past a rm Current consensus is that recent W changes are due to human activity r M Forcing system in unknown domain e danger of abrupt large changes in future not quite like in the day a er tomorrow 1 Fiwurv 772 Tmnd in m sumac Impammvl a we Enrlh qr norlh39m midlzmudus v r III lumprahquot mmmmmr m m lungplum quotcurd r5 hum mm prams a w c 1 FrumGraedelFE nd rummmmaspne c hangs Ems mPeSpaclrve NedmG Fveemzln regs m an mm W N Problems are often linked TABLE 1A Almosphuic Ema n Trace Gases Dumnszd Urban Sell39AClcaxung of Air Acid Vislbvlity Greenhousn Slramsphem Atmosphere Gas Pnlluunn Deposition lmpnirmem E cm omeplericn DecrezscsoH C02 17 CH l 1 so N30 17 NO NO N02 H7 so CFC or 7 rndicar hm A u 1 ch m m NH 5mm Gmrdel and lexcn11 9 Lecture 7 Photochemistry of Important Atmospheric Species Required Reading FP Chapter 4 Atmospheric Chemistry CHEM5151 ATOC5151 Spring 2005 Prof JoseLuis Jimenez Outline of Lecture General remarks 02 03 Nitrogen species Aldehydes and ketones CFCs We won t cover everything in class read the rest in the book 7 Have to know how to nd interpret quickly This lecture Reminder from last time Sunlight drives chemistry of trop amp strat Hot photons break bonds and create free radicals Radicals can react with many molecules Obj calculate rates of photolysis amp product generation Generic reaction A hv gt B C M dt JAA1 l aAltzgt AltzgtFltzgtdzx A J A rst order photolysis rate of A S39l a A x1 wavelength dependent cross section of A cmZmolec A x1 wavelength dependent quantum yield for photolysis F l spectral actinic ux density cm2s Last lecture General Remarks Photodissociation is the most important class of photochemical process in the atmosphere ABhv gtAB In orderto photodissociate a molecule it must be excited above its dissociation energy Do In the lower troposphere only molecules with D0 corresponding to L gt 290 nm are photochemically active Most common atmospheric molecules including N2 CO 02 C02 CH4 NO etc are stable against photodissociation in the troposphere In addition the molecule should have bright electronic transitions above Do For example HNO3 has a low dissociation energy D0 215 eV but it needs UV for its photolysis because it does not have appropriate electronic transitions in the visible In general both the absorption cross sections and photodissociation quantum yields are wavelength dependent Photoionization processes are generally not important in the lower atmosphere ionization potentials for most regular molecules gt 9 eV Table 24 Dissociation energies of selected molecules of atmospheric interest Dissociation energies Equivalent wavelength eV A Species 112 452 2743 CHA 455 2722 C2116 436 2844 C2114 480 2583 C H 576 2153 PH 340 0 NH 470 2637 1125 396 3134 H20 517 2398 H202 222 5582 51 7 0 110 11222 CO 1 114 1 113 C01 552 2247 H2130 382 3144 N2 980 1265 N10 173 7152 N0 655 1893 N02 3 18 3903 N03 216 5731 N105 099 12536 215 5774 110sz 101 12320 HCI 447 2773 CFCI 325 381 1 CFC12 346 3582 ClONO 116 10665 C120 077 16057 SO 5 40 2296 SO 5 72 2168 COS 320 3873 HCN 537 2309 HC3N 634 1955 C1N2 584 2123 From S Nidkorodov 02 Electronic Transitions 579 385 Energy ij 193 O From FPampP FIGURE 41 Potential energy curves for ground and rst four excited states of 2 5 K SchumannRunge system H Herzberg continuum A A atmospheric bands adapted from Gay Always start in ground state X32g39 Only transitions to triplet states are spinallowed X32g39 gt A3211 forbbiden because gt Occurs weakly Herzberg continuum 190300 nm X32g39 gt B321 is allowed SchumannRunge system 175200 nm bands due to different Vibrot states B321 crossed by 3Hu repulsive state dissociates to 03PO3P Later lt 175 nm spectrum is continuum dissociation of B32 to 03PO1D Dist C10 M1 10 16 I I I I l I I I I I I I I I I I I I I 02 phOtOIYSiS the 1017 200240 nm range is SCHUMANNRUNGE A 48 IONIZAT ON commuum the major source of N 10 E GONTINUUM O3 1n the stratosphere 2 10 19 a E i 02 can absorb nearly U a 104 SCHUtg XNNNDSRUNGE 2 all rad1at1on w1th k quot LYMAN 39 39 g 0 21 a H 10200 nm h1gh up 1n U I T the atmosphere 5 Io zz E 1043 H0 the Solve in class Estimate 0 spec rum g 02 coincident with HERZBERG the length Of alr COIumn lt 1022 m Lyman a line of commuum at P 001 Torr and T 5 H atom 200 K characteristic of 10 I I I l I I l I I I I l I I I I 39 39 39 50 100 50 200 I I I 250 80 km altitude reqUIred ygen From Brasseur and Solomon Fig 426 Spectral distribution of the absorption cross section of molecular ox to reduce the radiation flux at 150 nm by 10 orders of magnitude Neglect the fact that a substantial portion of oxygen is atomized at this altitude A 230 m WAVELENGTH nm 1a Absorption Cross Section 1039 1039 J iJvi u C 1 w quot5 1343 03 Q E 77 739 19 r x r 1 Eirnxmroz 1o lt 104 F m t 39 200 225 250 275 300 325 351 Wavelength nm small ux Some penetralion lo surface 10 ram 5 piffi f if f x vvItr r 39 10quot f fl Stmng E K 30 km N V 250 nm 4quot 1039s f 395 i v39 um 7 g 1010 MLJWquot Surface x mm o 7 1 2110 225 250 275 300 325 35a 3 Wavelength nrnl 5 UV absorption by 02 and O3 UV Cross sections httpWWW ccpo odu eduSEESozoneoziclass htm No penetration to surtace O2 Photochemistry V 39 L Schumann continuum very ef cient screening radiation below 200 nm Solar radiation more intense towards longer I Dissociation of O2 in Herzberg continuum 200 240 nm is very important for O3 in the stratosphere 02 hv gt 03P 03P C31 02 M a 03 Troposphere k gt 290 nm Not enough energy for O2 dissociation 03 from NO2 hv ALTITUDE km Fig 431 Contribution of each spectral molecular oxygen as a function of altitude u yuml From Brasseur and Solomon n uuxxnl Illll l 10quot 0 9 1039 10 7 1n 10 10396 PHOTODISSOCIATION COEFFICIENT 5quot region to the photodissociation of TABLE 42 Threshold Wavelengths for the Production of GroundSlate or Electronically Excited Oxygen Atoms from O2 Photolysisquot Threshold wavelength nm Electronic state of oxygen atoms o m 06 2424 0N 0 D 1750 or P 065 1331 quot l mm Okabc 978 h 03P is the groundstale species From FPampP Importance 0 03 Highly reactive Absorbs UV Shield surface from hard UV Central role in atmospheric chemistry Highly toxic gt health effects in humans Crop degradation gt billions of in losses Its photolysis produces O1D which yields OH OH is most important tropospheric oxidant Photolysis to O3P regenerates 03 not important Absorbs IR Greenhouse gas Ozone Electronic States Transitions into triplet states extremely weak forbidden All allowed excited electronic transitions lead to 03 above its lowest dissociation threshold Multiple dissociation pathways are available for O3 03 hv gt 01D 02a1Ag 03 hv gt 01D 02X32g 03 hv gt 03P 02a1Ag 03 hv gt 03P 02X3Zg 7 lowest Transition into the 1B2 state 255 nm Hartley band is strongest Weaker transitions into other singlet states at N600 nm Chappuis bands and 330 nm 03XIA1 030132 310 nm O1D 02a1Ag 411nm O1D 0206 612nm 0313 02a1Ag 1180 nm gt 3B1 3 0013 02x 2g Huggins bands From S Nidkorodov O3 Absorption Spectrum T I I 10quot r 1017 O J m 03919 020 ABSORPTION CROSS SECTlON cmz 1021 10 22 From Yung amp DeMore Hartley vlllvv 39 i From FPampP Huggins bands E 12 bands 3 10 x101 x102 x103 x104 9 a 03 Hartley 2 g 05 bands m E 04 f 02 Ea 39 I l 200 250 300 350 Mnmi Adapted from Dnumnni H al 19359 FIGURE 4 UV abwl39plion of 05 3 mum 1rmpcral un in the Hartley LnLl Huggins hands Al the longer wavelengths each curve hug licun expanded by the factor slidMi O Chappuis bands 1000 I 2000 I ll llll lllll 4000 5000 6000 WAVELENGTH A n I 3000 I n 7000 8000 O3 Photochemistry Most important aspect is production of 01D and thus OH 03 hV gt 02 0CD 1D z 90 below 305 nm 03 hV gt 02 03P 3P z 10 below 305 nm 01D H20 gt 2 OH OH yield z 10 at the surface 01D M gt O3P the rest of COD atoms are quenched 7 Dissociation threshold for 2 0 33m l 0 o 00 ITalukdare1al1993 03 hV gt 01D 02a1Ag 390 0398 390 is at 310 nm However O1D products A I are observed up to 330 nm because of p 05 g a dissociation of internally excited 03 04 9 which requires less energy to break 3 apart responsible for 306 325 nm 0 2 Threshold 3993993 o falloff Drops as Ti 9 9 00 i i i I V b spinforbidden process 39300 305 310 315 320 325 330 mm 03 W gt 01D 0232939 From FPampP FIGURE 49 Some measurements of the quantum yields for pro ductiun of or39D in the photolxsis of o a 293 K sole contributor A gt 325 nm fT Photodissociation Thresholds in W o o VAmerdingeiaszs l 039 3 l 7m NO2 and 03 W 390 For NO2 and O3 photodissociation quantum yields a 06 39 do not drop immediately to zero below the 3 dissociation threshold This effect is explained by 39 channeling the internal energy of molecules into 02 Threshold oeg39g the dissociation process Yea9 o 0 90 D0 K A B New aria aim sis an 325 v 3 n 3 nm FIGURE 49 Some measurements of the quantum yields for pro duction of 01D in the photolysis of 03 at 298 K From FPampP l 385 390 395 400 405 410 415 1 nm w 9 3 g 11 E 6 10 813 0 8 6 o o E 8 8 E 6 08 E g 07 8 m g 06 Threshold 5 6 e 05 5 0 4 O 3 o a g g 39 Internal energy 5 0392 Collisions g x 01 a LLI 00 m FIGURE 4 12 Quantum yields for NO production in the photoly sis of N02 at 298 K Calculated quantum yields due to intern energy dotted line the calculated dissociation due to collision AB dashed line and the sum of these two calculations solid line are From s Nidkorodov also shown adapted from Roehl et all 1994 O3 Photodissociation Channels I I I ITTI II I T I IIIIII I I I l I I T I llll 5 o3 40 sec x 1und 2 E 2 30 E 1 CHAPPUIS E 2 HUGGlNS E 3 HARTLEY 20 l R lt 210 nm P 10 ill llli I IllIll IIlIlli r I llllll 10quot5 10 5 10quot 10 3 to PHOTODISSQCIATIQN COEFFlCIENT 5 Fig 435 Contribution of each spectral region to the total photodissociation of ozone as a function of altitude From Nicolet 1980 Combined UV Shielding by 02 and O3 02 takes care of 90 of deep UV radiation well above 80 km ie in the mesosphere and thermosphere O3 important below 40 km Window at 210 nm between 02 and O3 absorption of paramount importance for making 03 in stratosphere Via photolysis of 02 120 From Warneck E Fig 2 9 x IIJ 80 O D Z quot39i 4 0 ISO 200 250 300 WAVELENGTH Inm Fig 29 Elevation at which solar radiation is attenuated by 02 and 03 by one order of magnitude Table 41 Spectral regions of photochemical importance in the atmosphere Wavelength Atmospheric absorbers 1216 nm Solar Lyman a line absorbed by 02 in the meso sphere no absorption by 03 100 to 175 nm 02 Schumann Runge continuum Absorption by O2 in the thermosphere Can be neglected in the mesosphere and stratosphere amp 175 to 200 nm 02 Schumann Runge bands Absorption by 02 in the mesosphere and upper stratosphere Effect of 03 can be neglected in the mesosphere but is im portant in the stratosphere 200 to 242 nm 02 Herzberg continuum Absorption by 02 in the stratosphere and weak absorption in the meso sphere Absorption by the O3 Hartley band is also important both must be considered 242 to 310 nm 03 Hartley band Absorption by 03 in the strato sphere leading to the formation of 01D 310 to 400 nm 03 Huggins bands Absorption by 03 in the stra tosphere and troposphere leads to the formation of 03P 400 to 850 nm 03 Chappuis bands Absorption by 03 in the tro posphere induces photodissociation even at the sur face From Brasseur amp Solomon Photolysis Rates for O2 N02 and O3 0 I V I Typical values for photodissociation i coef cients J for O3 02 amp NO2 as a anction rom ung e ore 3 of altitude Photolys1s rate for 021s strongly 39 altitude dependent because the lower you go the less UV radiation capable of breaking O2 is available selfshielding Photolysis rate for 03 becomes altitude dependent below 40 km for similar selfshielding reasons On the contrary Visible NO2 photolysis occurs with about the same rate throughout the atmosphere because Attitude km S 2quot 39 there is not enough of it for selfshielding 50 l l I From E Warneck 0 0 our39 mquot 10quot mquot 031 f 0 J 2 J 3 Photodilmiatlon Coef cient all 3 3o 39 3 Figure 225 b Photodissociation coef cient for 03 03 hv 39 02 000 and no2 N02 hv N0 0 in Earth s atmo L 20 sphere The dotted line gives the contribution of the direct attenuated lt solar ux the solid line gives the sum of the direct and diffuse uxes I l l The calculations are diumally averaged for a midlatitude atmosphere 101015 1013 1039quot 1o 310quot in spring with surface re ectivity of 025 and without aerosols The l total ozone column in the model is 341 DU Dobson units From PHOTOD39SSOCIATION COEFFICIENT I s the authors CaltechJet Propulsion Lab model of Earth s atmosphere See for example Michelangeh D V Allen M and Yung Y L WE Based on the gures Show here 1989 E1 Chichon Volcanic Aerosols Impact of Radiative Thermal eSt39mate the I39fel39m of N02 02 and O3 agamSt and Chemical Perturbations J Geophys Res 94 18429 Ph t d39ss 39at39 at 20 km and 50 km Structure of Important NSpecies Nitrogen Species Molecular nitrogen Nitric oxide Nitrogen dioxide Nitrate radical N2 NO N03 N03 F N O N E N NO quot0 O 39O HN O Nitrous acid Nitric acid Peroxynitric acid Nitrous oxide HONO HNO3 HOzNOz N20 H O o N 11 2 H O O WLNWO ON O N HO O O Dinitrogen pentoxide N205 O O NON 0 From Jacobson 1999 Table B O o posted on course web page Many other species there useful when you don t know detailed structure Atm Pro les of Important N Species Ni i39Rt itiliN Sl lfiflii Pilarch I5 iLiULii Norn 411 N i Important N a h39gN t 39 Iii quotlr I l 2 l iii I I inr I39iTIi I I IIJIZ39I39IifquotIIIY39 quot IIIIIIIJL I lWLIII I ro39llllll 39 IIIIII Illllllll 39 containing molecules in lower atmosphere extremely photostable 397 N20 and HNO3 m easilydegradable N02 N03 and N205 HOZNO2 multitude of poorly quantified organic nitrates RONO2 most N N2 fx IIle nitrates are relatively stable towards UV Niij rlii NI 5 It lI J Total Density I I x Generally 39 concentrations are inversely proportional to photodissociation K I i I ifquot I I39 I quot I IN I From NASA HQ Number Densin Inrilerulcs term 391 ml In to reaction rates in the atmosphere 225K 295K Absorption Spectra and Photolysis Rates of Selected N Species Note sensitivity of zoo n I l 3W WAVELENGTH 139 nm FIGURE 215 Absorption spectra of C02 H20 N20 HN03 H101 and N205 From data in De More at a 1994 Baulch et ai 1982 and Atkinson et a1 1989 data for CO2 are from 1 Ogawa 1971 Solve in class Estimate the photodissociation lifetimes of N20 and HONO at 20 km Compare those with characteristic times for vertical transport in the stratosphere z 2 years FromS Nidkorodov l photolysis rates to shape of absorption spectra l I I n I I 350 ALTITUDE km CFZCIZ H202 O I x l l I 10quot 10398 10quot 10 10392 PHOTODISSOCIATION COEFFICIENT squot FIGURE 219 Photodissociation coef cients for several photochemically active atmospheric trace components as a function of altitude Data for H20 are from Park 1974 for an overhead sun for N20 and HNO3 from Johnston and Podolske 1978 for global average conditions for CFZCI2 from Rowland and Molina 1975 for an overhead sun and for H202 N205 HNOZ and N02 from Isaksen et al 1977 for a 60 solar zenith angle lO Nitrogen Dioxide NOZ m Photolysis ofNo2 generates ozone in the troposphere N 06 P 02 M gt No2 Absorption cross sections are structured and have a nontrivial dependence on 11 m axlu quot9 3 o 3 a g 8 mo 4 m2 quot 0 ES UN 2 E 8 me s Nidknmdav SEIEI 35D 4mm 45m Wavelength nm Photochemistry of NO2 Photolysis occurswth nearly 100 yield below 397 8 nm Oratom immediately makes 03 N0 hv NO 06 o lgtoM o1 n escence Above 410 nrn electronic excitation ofNo2 can result in the following processes o No hv F uor N0 01 N0 012 AQ N0 N2 yNo2 Nv N0 N0 N0 No1 Calculnlcd Wavelengths not or TABLE 41 Noz Phololysis Bcluw Wine on Fmgmnnts Shown cnn d dquotquot B Pm me omen onnns NO XII 3978 39 1507 A1 i441 v7 73 quot From 0 be 19 quotAssuming no conirilmiinn from micrnol energy oi the molecule Electronic energy Lransfer Elecunnicrmrvibmtiunzl energy Lransfer Disproportionatiun lab conditions unlv i i and mono enEfgy r Ce39hsmn sea Jan 395 in 405 no no mm HGURE 412 Cu mum Vlchh In No mulmliuu n on nuth are or M n 2 K comm ninnnm y le an n nnnni may dulln loci on autumn dwmiuu w n em on dmhm not ml m M a nice Mu Awhilin new one an u Nitn39c Acid HNO3 HNo1w gt0HNo2 HNOhv gtOHO o HNo1w gtHNo3 Overall relatively long lifetime against photolysis ii s between 200 and 315 nm requires Vacuum UV39 0 is only 003 at 266 nm requires Vacuum UV39 0 is only 0002 at 266 nm a 5 o E E E w 39 ii 200 220 240 260 250 300 320 am Wavelenglri irimi FIGURE 4 13 Abwrpuml specimni tit No nlid mic 2i 392 K Symbols represent data rcpiincu iii previom mmi 1mm mth ih r 1993 Overcome Dissociation vibrational energy into molec ethan its dissociation ene gy e e Energy cm 1 HOONO 20000 15000 10000 5000 rm 5 Nxdknmdnv EX l Nearyii ifi ai ed excitation of 2V1 overloi39ie ll i HOONO Will breakit ii ito OH arid NO2 HONo2 Ex 2 visbie excitation ortsv1 ii i HNO3 Will also break it into OH and no2 Such overtone dissociation is a very indirect process involving highly inerricient intermolecular vibrational energ With collisional Stabilization fone supplies enough IR f V39J fi 39 a a uemor image r Dnth molecu maybreak Nitrous Acid HONO 39HONOhV 0HNO zlbelow400nm HONO like N02 has strong absorption in Visible and a highly structured spectrum Its photochemical lifetime in the atmosphere is a few minutes Ver important as source of OH radicals in the morning base a m m m From ier 1Clg 6 cm2 molecule39 310 330 350 370 390 A nm FIGURE 414 Absorption specrrum of HONO m 277 K adapted from Bongzmz 0111 IU9I Now lhal lhc absoluu values of lhc crass scclions shown llurc should be mulliplicd by 1855 as recommended by Hongarlz u I 1994 Sources of HOX OH H02 in Mexico City HOx drive smog and secondary aerosol chemistry HONO photolyzes at long A very important in early morning HCHO formaldehyde is dominant source 03 source needs to wait for O3 to be produced depends on others HONO HCHO Ozone OLE GIyCCHO 8 14 49 30 3 04 10 sum HON0 hv HCHO hu A 03 hu 03 alkenes 1o7 1o6 39 l EM r N Glyoxal hv quot 7CCH0 hv HOX production cm39ss39l 12 18 24 Fromiz VolkamerampW Brune MIT ampPsU Time Of day hours Pernitric Acid HO2NO2 HOZNO2 hV gt HO2 NO2 quantum yields uncertain 065 recommended HOZNO2 hV OH N03 1 z 035 at 248 nm more measurements needed Unique in that it can be broken by nearinfrared radiation This is important at large SZA with orders of magnitude larger NIR vs UV H02N02 hv nearIR gt HOZNOZ v12 gt Ho2 N02 1 z 025 P amp T dep 395 r a a 30 g 1125 0 m h 3 m a D 3 900 quota E E 55 e E O E E 450 N N E E g 225 4 e 393 quotI 535233912 41 ng quot 21G 24E 27C 30039 33G 739 39 39 I 39 39 39 Wavelength nm Wavelength nm FIGURE 415 Absorption spectra of HO NC at 298 K in the a 7 l 39 F33 1 df S39n J WI ll to Bill nm and b ZED to I run regions adapts rum 1 gm 9 all Well 250 Nitrate Radical NO 3 6 2030 NO3 1s Important 1n n1ghtt1me chem1stry It r mm 39l E u has unusually large cross sect10ns 1n the red gt g Jail photod1ssoc1ates 1n seconds 1n the morn1ng NE 1mm I Ii 5quot I NO3 by gt N02 03P l j l l is 7 dependent important towards the blue 9 5m NO3 by gt NO 02 l J 1 O 77 I J I is 9 dependent important in the red competes 50 520 5 0 55 with fluorescence this process is nearly 2 my themoneuual bUt it is inhibited by a tall energy FIGURE 416 Alwsnrptkm speelrum of ND ml 193 K ludapled barrier from Dullion I LIL l J bund rm lutsl Emm Rilvi himk m and Mnuldin 19M Sander ll Jth and CanaanMilk t I ul El JHTJl N022A103P l39quotquot39N02 0 x 50 E 0 8 39 3 1 2 1 lt2 39 I 7quot 40 NO HHOM 9 E 06 I Fluorescence B 3 I g 30 No in 02 1A9 g 04 NO 02 5 I a 20 0 02 I B I II I l I 39 I 39 39 quotIn LE 10 590 600 610 620 630 640 NO2139I 02 329 A nm NOSFA a I FIGURE 418 Quantum yields for N03 photolys1s dotted llne N03 gt N02 0 solid line N03 gt NO 02 dashed line uo EIGUIEEf39EgIgsfnergems 0f N03 Phowdlss mamm adapmd from rescence quantum yields adapted from Johnston et al 1996 avrs e a Nitrous Oxide N20 0 N20 is extremely longlived because it is unreactive and it does not absorb much above 200 nm Below 200 nm N20 hv gt N2 01D Note this is a popular laboratory method of generating GOD I z 1 0 Subsequent reactions of 01D with N20 lead to production of other nitrogen oxides in the stratosphere N20 01D gt NO NO major source of NO in the stratosphere gt N2 02 competing step 0 Because of its stability N20 is used a TE 1 1 1 1 1 1 1 1 From 5 3000 250T Galvan 395 2400 200 amp Pitts g E 1500 A 150 E 3 1200 a 100 E g 600 50 3 a lt i 4 1 1 1 4 l 1 1 1 l 1 1 1 1230 1290 1350 1410 1470 1530 1391 1111111111111 9 0 I l 9 o l l P o I 1i11i1l 3 o l l Absorption coefficient cm 391 atm quot 1 I 1 1 I 1 1 1 1 1 1 1 1 1 l 1 1560 1390 1625 1675 1800 2000 Wavelength A Fig 343 The absorption spectrum of nitrous oxide N20 From Zelikoff Watanabe and Inn quotnewer Concentrations of other molecules Solve in class Find a conversnon between are often compared to that of N20 to see is they are well mixed absorption coefficient in cm1atm1 an cross sections in cm2 at room temperature Evaluate N20 cross sections at 193 nm using the data shown here Formaldehyde HCHO Two competing photodissociation channels HCHO hv gt H HCO a HCHO hv gt H2 co b 0 Channel a leads to HO2 radical production via H02M gt H02 19 HCO 02 gt Ho2 C0 20 0 Sources of H02 are effectively sources of OH because Ho2 NO gt OHNo2 17 39939 1020fcm2 Remember HCHO is dominant HOX source in Mexico City 0 H2 00 39 08 05 04 02 260 280 300 320 WAVELENGTH nm 340 360 FIGURE 218 Absorption spectrum and quantum yields for the two photodecomposition channels of formaldehyde in air at atmospheric pressure From the data of Clark et al 1978 Horowitz and Calvert 1978 Tang et al 1979 and Moortgat et al 1979 1983 15 Acetaldehyde and higher aldehydes Four possible photodissociation channels CH3CHO hv gt CH3 HCO CH3CHO hv gt CH4 CO CH3CHO hv gt CH3O H CH3CHO hv gt CHZCO H2 Can also be HOX source Similarly for higher aldehydes a b C d a 7 it C Hai iIEiECHD ED h39J 39I39 g 5 99 iEH3JECHCHO ui quotIquot w39 2 ii g a it EHECHECHD i E quotx 39 E E 2 c 2 a 5 l It 1 m From FPampP FIGURE 42 Absorptinn spectra for sumo simple aldehydes adapted mm Martinez c at l J J l Process Quantum yield AH298 K Threshold Note a CH3HCO 0 05 84 7il 2 kcalmol z 338 nm b CH4CO 0 05goes up inUV 4 6 kcalmol none Large barrier c CH3O H lt 0 01 above 290 nm 95 8 i1 2 kcalmol z 298 nm d CHZCO H2 0 28 7 i3 kcalmol z 1000 nm Large barrier Acetone CH3COCH3 Two main photodissociation channels CH3COCH3 hv gt CH3 CH3CO a CH3COCH3 hv gt 2 CH3 co 0 a more important near the earth surface Photodissociation competes with collisional relaxation 1 Pdependent Also a competition between photodissociation and reaction with OH CH3COCH3 hv gt CH3COCH3 M gt CH3COCH3 Quenching CH3COCH3 OH gt CH3COCH2 H20 l 260 280 300 320 340 Mnm FIGURE 430 Measured quantum yields for acetone photodisso ciation as a function of wavelength at 1 atm total pressure and extrapolated to zero total pressure adapted from Gierczak et al 1998 b 7 From F PampP 10 10 6 Threshold 338 nm Threshold 299 nm Reaction with OH 20 Reaction 15 x with CH Altitude km a l k 51 FIGURE 43 1 Calculated rstorder rate constants for loss of CH 3COCH3 due to reaction with OH ie kOH or photolysis ie kp as a function of altitude adapted from Gierczak et 11 1998 l6 Chloro uorooarbons CFCs 5 ABSORPY lON CROSS SECTlON m 3 Photolysis Rates 50 1 Absorption Spectra r uuml u llHHlI I rmml llHHHi h o ALTITUDE km yummy urnnu Illrum xlvlvyll I c502 CF03 CHJCI curcrz CriscoJ HALOCARBONS FHOTODISSOCIATION sec X Z lllllllll lllllllll l Illlllll I llllllll io 7 10 0 PHOTODISSOCIATION COEFFlCIENT 5quot s Fig 4454 Vertical distribution of the photolysis rate of several chlorocarhons E o i x 2v 7 m g E o t o 1 l I l I 1 0 mo Iso 200 210 220 2 o WAVELENcrHrnm Fig 453 Spectral distribution of the absorption cross sections of several halo No other CFC sinks than photolysis Known that Cl would destroy O 1995 Nobel Prize MampR is the idea in this slide CFCs will provide large source of C1 in stratosphere and lead to O3 carbons and their temperature dependence From VanlaethemMeuree at a 1978 From Brasseur and Solomon l7