SPTP MESO MODELING
SPTP MESO MODELING ATMO 689
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This 17 page Class Notes was uploaded by Demarcus Schaden V on Wednesday October 21, 2015. The Class Notes belongs to ATMO 689 at Texas A&M University taught by Staff in Fall. Since its upload, it has received 25 views. For similar materials see /class/225951/atmo-689-texas-a-m-university in Atmospheric Sciences (ATM S) at Texas A&M University.
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Date Created: 10/21/15
Spectroscopy in Atmospheric Science Spectroscopy used for many atmospheric science analytical questions Solar spectroscopy Direct absorption or scattering in atmosphere eg DOAS Remote sensing from space eg UARS GOME etc UVvisIR absorption spectroscopy eg for ozone H2O CO2 CH4 CO etc Fluorescence spectroscopy High specificity sensitivity and resolution lab studies Increasing amount of fieldbased instruments for important atmospheric species such as HOX etc Very specific and sensitive techniques Absorbing molecule 002 C02 002 02 CO2 H o sz39L H20 1 0a H20 0a H20 1 o on o Transmittance N J 0 O O O O I I I I I I I I I I I I I I I I 012 3 4 5 6 7 8 9101112131415 Wavelengthum near middle I lar llt gtllt Infrared a Infrared infrared Absorption 34 12 14 b Wavelengthum Figure 23 Absorption properties of the earth s atmosphere and of some of its major constituents in the infrared region of the spectrum a Horizontal absorption spectrum measured over a distance of 1800 m at sea level Reproduced from 6 Fig 46 p 140 b Vertical absorption spectrum of the earth s atmosphere and absorption of individual compounds Reproduced with permission of Les Editions Physique39 from 7 Fig 4 p777 Some important relationships Transition dipole moment ukl Tensor for which u 0 for transition between states k and l Absorption Luk2 ltkulgt2 N2 and 02 do neither have a permanent dipole such as H20 nor an induced dipole gt no nonelectronic absorptions Optical Density OD l l0 x 1000 OD le l path length C concentration a specific absorptivity lt9 N Lukil2 ABhv gtAB gt AB is an exited often unstable state of molecule AB for an electronic transition due to absorption of UVvis light AB has a different electron configuration than AB for an infrared absorption AB rovibrates stronger than AB gt are processes of the following relative importance in the atmosphere 1 thermal nonradiative decay eg greenhouse heating 2 photolysis eg ozone in stratosphere 3 fluorescence eg NO is thermosphere 4 phosphorescencenegligible VB 667 cm1 VS 1388 cm1 VB 667 cm VAS 2349 cm1 Bending modes Stretching modes Figure 74 Representation of the two stretching modes and the two bending modes of 002 For the stretching modes we indicated three different positions The bending modes correspond to two orthogonal planes which are physically equivalent and therefore have the same frequency 1H37quot1 1H jsc1 1 1 I Slog 1 Mm RvBrancn Absorphon 1 l A L Vd s V 1 1 2800 I 1 v cm 1j PBranch Figure 73 Highresolut39ron vibrationalrotational spectrum of HCI The lines appear in pairs because the spectrum re ects the presence of both H35C and H37C in their natural abundance ratio of 31 The AJ O branch 393 absent in these spectra Adapted and reproduced by permission of Oxford University Press from 1 Fig 1814 Figure 77 Schematic representation of the sequence of events leading to fluorescence triplet formation and phosphorescence Note that the maximum in the fluorescence spectrum again will correspond to the transition with the largest Franck Condon factor electronic excited state vibrational wave function having maximal overlap with ground state electronic ground state Figure 76 Illustration of the Franck Condon principle in molecular spectroscopy The recess of absorption of a photon corresponds to a purely vertical transition in this diagram which means that the relative position of the nuclei does not change during the fast excitation process The electronic ground state is denoted by So and the first excited electronic state by 8 Higher electronic states would be denoted by 82 etc Within the graph of the electronic states the vibrational wave functions are indicated The most intense vibronic transition occurs from the ground state to a vibrational level of the excited state for which the overlap of the vibrational wave functions is maximal Side View Mirror Lens Cell A or B Tn Window Source ll 2 Thermoelectric Cooler H20 Detector Dichroic Beam Chopplng Shutter H20 Filter Spli er GO Detecto 002 Filter 2 39 Thermoelectric Cooler Figure 11 Schematic of LI 7000 optical path Standard NO2 uorescence NOinstrument SAMPLE N0 MODE TEFLON FLOW PAR39RCULATE N0 sENsoR FILTER 0 MODE HLTER WWW NC SOLENOlD 1 ELECTRONICS NozNO CONVERTER PRESSURE REACT ON NOXMOD TRANSDUCER CHAMBER DRYNR 1 4 PMT L FLOW CAHLLARV K SENSOR OZONATDR OP HCAL HLTER CHAMBERPUMF S tandard Gas Filter Correlation infrared abso tion COinstrumen t Mode JSCII r FLOW DIAGRAM HEC vumrs pymmmy w Deiscwr Fm Samu e e1 Fmer mm mm Pump Trace Gas exchanqe processes with soil only with vegetation NO N20 CH4 H2 CO2 CO with soil ozone C02 CO VOCs eg isoprene NHs N02 HNOs etc cos H28 DMS COS SO 3 2 Ozone alkyIhalides Wlth ocean NH co2 co 3 VOCs DMS COS etc Methods to measure trace gas fluxes Enclosures for smallscale Micrometeorological measurements Techniques for integrative Static method measurements Isolated air mass monitoring mean gradient or Bowenratio Commonly used for airsoil method eXChange measures species for which no Dominantly usedfor low fast sensor exists emrssrondeposrtton eg CH4 Eddy Covariance EC Dynam39c meth0d3 Standard technique using fast Constant air mass renewal sensors eg COZHZO Commonly used for airplant Relaxed Eddy Accumulation exchange REA Domi antly USGWOF high Modified EC for adaptation of emrssrondeposrtton eg C02 Slow sensors Used for VOC and other fluxes t2 A t1 12 O W soil T deg C Sonic anemometer time series 31 3 30 7 77 2 29 7 77 1 I A 28 7 l l 77 o 27 7 7 1 26 7 7 72 25 1 1 1 1 1 1 73 143422 143457 143531 143606 143640 143715 143749 143324 local time w m s1 1 w39ms Q w 390 A t 031 o
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