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’