1. The Atmosphere: Oxidizing Medium In Global Biogeochemical Cycles EARTH SURFACE Emission Reduced gas Oxidized gas/ aerosol Oxidation Uptake Reduction

2. Only A Narrow UV Window (300-320 nm) for O( 1 D) Production 30 o equinox midday Solar spectrum

3. O( 1 D) production in the troposphere?

4. OH Radical: Main Tropospheric Oxidant O 3 + hv  O 2 + O( 1 D) (1) O( 1 D) + M  O + M (2) O( 1 D) + H 2 O  2OH (3) Primary source: Sink: oxidation of reduced species CO + OH  CO 2 + H CH 4 + OH  CH 3 + H 2 O HCFC + OH  H 2 O + … Major OH sinks globally GLOBAL MEAN [OH] = 1.0x10 6 molecules cm -3

5. QUESTIONS 1. How would a thinning of the stratospheric ozone layer affect the source of OH in the troposphere? 2. How might global warming affect the source of OH in the troposphere?

6. Global Sources of Methane Natural Sources Anthropogenic Sources

7. Global Distribution of Methane NOAA/CMDL surface air measurements

8. Historical Trends In Methane Historical methane trend Recent methane trend

9. RECENT TREND IN METHANE

10. Global Sources of CO

11. Satellite Measurements of Lower Tropospheric CO

12. Satellite Measurements of Upper Tropospheric CO

13. Global Distribution of CO NOAA/CMDL surface air measurements

14. O3O3 O 3 + hv  OH + OH H2OH2O Stratosphere COCH 4 1-2 x10 13 moles yr -1 2-4 x10 13 moles yr -1 6-10 x10 13 moles yr -1 3 x10 13 moles yr -1 OH only from strat O 3 would be titrated X Troposphere How are tropospheric OH levels maintained?

15. Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS- CHEM model results for 1997 (contours). GEOS-CHEM tropospheric ozone columns for July 1997. GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE Li et al. [2001]

16. NO x EMISSIONS (Tg N yr -1 ) TO TROPOSPHERE FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2

17. MAPPING OF TROPOSPHERIC NO 2 FROM THE GOME SATELLITE INSTRUMENT (July 1996) Martin et al. [2002]

18. LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA

19. PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NO x

20. NO x, HNO 3, AND PAN OVER THE TROPICAL PACIFIC Aircraft observations from PEM-Tropics B, March-April 1999 Staudt et al. [2003]

21. QUESTIONS 1. The prospect of hydrogen-fueled cars is leading to study of the effect of increasing atmospheric H 2. Would you expect H 2 to be oxidized by OH? What would be the effect on the oxidizing power of the atmosphere? 2. Loss of NO x in the troposphere takes place by NO 2 +OH, same as in the stratosphere. What is the effect of this reaction on tropospheric ozone?

22. QUESTION 1. How does the lifetime of NO x respond to a change in the NO x concentration? If NO x emissions were to double, would NO x concentrations more than double or less than double?