ATMOSPHERIC CHEMICAL SYSTEMS October 1992 Source: NAsa
ATMOSPHERIC CHEMICAL SYSTEMS Source: NASA
IMPORTANCE OF ATMOSPHERIC CHEMISTRY Climate Change Stratospheric ozone ATMOSPHERIC CHEMISTRY Regional air pollution Acid Deposition
ATMOSPHERIC CHEMISTRY Climate Change Regional Air Pollution Acid Deposition Stratospheric Ozone IMPORTANCE OF ATMOSPHERIC CHEMISTRY
ATMOSPHERE STRUCTURE BULK COMPOSITIon Atmospheric pressure(millibars-mb 02004006008001000 120 80 Temperature Pressur 100 Thermosphere Pressure units Mesopause 1atm=1013×106gcms2 Mesosphere 1 mbar 103 g cm-Is-2 g60 40a Stratopause 1 hPa= 10 g cm-ls2 40 Stratosphere. Ideal gas law Tropopause 20 (p R T)/Ma Troposphere 4048012 Temperature(°c) Source: Environmental Science, Cunningham, P. W and B. W Saigo, 200/
ATMOSPHERE STRUCTURE & BULK COMPOSITION • Pressure units 1 atm = 1.013 x 106 g cm-1 s -2 1 mbar = 103 g cm-1 s -2 1 hPa = 103 g cm-1 s -2 • Ideal gas law p V = Rg T p = ( Rg T)/Ma Source: Environmental Science, Cunningham, P. W. and B. W. Saigo, 2001
ATMOSPHERIC TRANSPORT TIME SCALES 2 weeks 1-2 months Equate stratopause tropopause ..--... 5-10yr mo PBL top wk (1-3 km)1-2 days surface Source: Introduction to Atmospheric Chemistry, Jacob, D.J., 1999
ATMOSPHERIC TRANSPORT TIME SCALES Source: Introduction to Atmospheric Chemistry, Jacob, D. J., 1999
TYPICAL ATMOSPHERIC COMPOSITION (mole fraction) ypical units 0.78 Number concentration molecules cm-3 02 0.21 Mixing ratio: ppm, ppb, ppt Ar 0.093 <0.0001-0.04. Molecular weight of air CO2 370 ppm Ma=28.96 g mole-I CH4 ppI 10 ppb-10 ppm Trace chemistry co 50 ppb-300 ppb Reactants are present in trace amounts NO ppb-1 ppt OH pp
TYPICAL ATMOSPHERIC COMPOSITION N2 0.78 O2 0.21 Ar 0.093 H2O <0.0001-0.04 CO2 370 ppm CH4 1.7 ppm O3 10 ppb – 10 ppm CO 50 ppb – 300 ppb NOx 5 ppb – 1 ppt OH < 1 ppt (mole fraction) • Typical units Number concentration: molecules cm-3 Mixing ratio: ppm, ppb, ppt • Molecular weight of air Ma = 28.96 g mole-1 • Trace chemistry Reactants are present in trace amounts
OXIDIZING NATURE OF THE ATMOSPHERE Earth's atmosphere is oxidizing due to presence of o SO2--> SO42-: CHA-->CO CO-->CO2: NO2 -> HNO3 Radicals are oxidizing agents in the atmosphere OH is the cleansing agent of the atmosphere Key to understanding atmospheric oxidant chemistry Understand radical cycling but radical cycle is intimately connected to oxidant chemistry of other trace compounds including O3 Start with O3 O3 is important from chemical, climate, and health perspectives
OXIDIZING NATURE OF THE ATMOSPHERE • Earth’s atmosphere is oxidizing due to presence of O2 SO2 --> SO4 2- ; CH4 --> CO; CO --> CO2 ; NO2 --> HNO3 • Radicals are oxidizing agents in the atmosphere OH is the cleansing agent of the atmosphere • Key to understanding atmospheric oxidant chemistry Understand radical cycling → but radical cycle is intimately connected to oxidant chemistry of other trace compounds including O3 • Start with O3 O3 is important from chemical, climate, and health perspectives
ATMOSPHERIC O-A BRIEF HISTORY 199-1869 Christian Frederich schonbein 1840: Ozone discovered in 1840 by C f. Schonbein thought it was made up of oxygen and hydrogen 1848: Systematic measurement attempts- curiousity, growing interest in env, health effects, 'economy of nature 1861: Odling suggested that ozone was O3 1930: Chemical mechanism for O3 layer postulated 1952: O3 identified as component of chemical smog
ATMOSPHERIC O3 – A BRIEF HISTORY • 1840: Ozone discovered in 1840 by C. F. Schönbein – thought it was made up of oxygen and hydrogen • 1848: Systematic measurement attempts – curiousity, growing interest in env., health effects, ‘economy of nature’ • 1861: Odling suggested that ozone was O3 • 1930: Chemical mechanism for O3 layer postulated • 1952: O3 identified as component of chemical smog Christian Frederich Schönbein
OZONE AND HEALTH Source: Stratospheric Ozone, NASA/GSFC Absorption Cross Section 10 60 10 510 18 50 10 40 o。*10 10 200 250 275 300 350 30是 Wavelength(nm) Solar flux 20 00 Top of the atmosphere 10 10.0 10 0369 DNA Action spectr M ixing Ratio Surface (ppmv) 12 300 320 Wavelength(nm) 90% of O3 is in the stratosphere; O3 layer with max w 9 ppm Absorption of n= 200-320 nm(UV-B and Uv-c)by strat O3
OZONE AND HEALTH • 90% of O3 is in the stratosphere; O3 layer with max ~ 9 ppm • Absorption of = 200-320 nm (UV-B and UV-C) by strat. O3 Source: Stratospheric Ozone, NASA/GSFC
OZONE AND STRATOSPHERIC TEMPERATURE Atmospheric pressure(millibars-mb 02004006008001000 120 80 Temperature 60 Pressure 100 Thermosphere 50 Mesopause 40 Mesosphere 40 9g>0g 30 Stratopause 20 Stratosphere 20 10 Tropopause 0 Troposphere 0369 Temperature°c)120 80-4004080 M ixing Ratio (ppmv) Source: Emvironmental Science, Cunningham, P. W and B W Saigo, 2001 Source: Stratospheric Ozone, NASA/GSFC Local heating of the stratosphere due to UV absorption by O3 Tropospheric O3 is also an important greenhouse gas
OZONE AND STRATOSPHERIC TEMPERATURE • Local heating of the stratosphere due to UV absorption by O3 • Tropospheric O3 is also an important greenhouse gas Source: Stratospheric Ozone, NASA/GSFC Source: Environmental Science, Cunningham, P. W. and B. W. Saigo, 2001
OZONE AND ATMOSPHERIC CHEMISTRY Solar radiation O(3P) wavelength 290-320 nm (D) 20H HO O3 is the primary source of tropospheric Oh >OH is atmospheric ' detergent
O3 O(1D) O(3P) 2OH Solar radiation, wavelength 290-320 nm H2O O2 , N2 O2 OZONE AND ATMOSPHERIC CHEMISTRY • O3 is the primary source of tropospheric OH → OH is atmospheric ‘detergent’
