大气环境化学教学课件电子教案全套课件四.pptx

ATMOSPHERIC CHEMICAL SYSTEMSSource: NASAIMPORTANCE OF ATMOSPHERIC CHEMISTRYClimate ChangeStratospheric OzoneATMOSPHERICCHEMISTRYAcid DepositionRegional Air Pollution 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)/MaSource: Environmental Science, Cunningham, P. W. and B. W. Saigo, 2001ATMOSPHERE STRUCTURE BULK COMPOSITIONATMOSPHERIC TRANSPORT TIME SCALESSource: Introduction to Atmospheric Chemistry, Jacob, D. J., 1999(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 TYPICAL ATMOSPHERIC COMPOSITIONOXIDIZING NATURE OF THE ATMOSPHERE Earth’s atmosphere is oxidizing due to presence of O2SO2 -- SO42-; 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 O3O3 is important from chemical, climate, and health perspectivesATMOSPHERIC O3 – A BRIEF HISTORYChristian Frederich Sch?nbein 1840: Ozone discovered in 1840 by C. F. Sch?nbein – 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 smogOZONE AND HEALTHSource: Stratospheric Ozone, NASA/GSFC 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. O3Source: Environmental Science, Cunningham, P. W. and B. W. Saigo, 2001Source: Stratospheric Ozone, NASA/GSFC Local heating of the stratosphere due to UV absorption by O3 Tropospheric O3 is al