1. This Week—Tropospheric Chemistry READING: Chapter 11 of text Tropospheric Chemistry Data Set Analysis

2. The Atmosphere: Oxidizing Medium EARTH SURFACE Emission Reduced gas Oxidized gas/ aerosol Oxidation Uptake Reduction

3. O( 1 D) Production in Troposphere? 30 o equinox midday Solar spectrum Actinic Flux vs wavelength (O 1 D production requires < 320nm)

4. O( 1 D) production in the Troposphere?

5. 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

6. 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 rate of OH in the troposphere?

7. Natural Sources Anthropogenic Sources Global Sources of Methane

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

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

10. Global Sources of CO

11. Satellite Measurements Lower Tropospheric CO

12. Upper Tropospheric CO Satellite Measurements

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

14. O3O3 O 3 + hv  2OH 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 OH Titration Problem

15. OH CH 3 O 2 CH 3 O HO 2 NO CH 4 O2O2 NO H 2 CO O3O3 NO NO 2 CH 3 O 2 HO 2 h O O2O2 O 3 + h H 2 CO + h H2OH2O O2O2 CO O2O2 HO x and NO x Catalyzed O 3 Production

16. Questions 1.NO also reacts with O 3 (as in the stratosphere) to produce NO 2. In fact, the rate of conversion of NO to NO 2 is dominated by this reaction in the troposphere. What is the effect of this reaction on O 3 production and HO x cycling? 2.Loss of NO x in the troposphere takes place by NO 2 +OH  HNO 3, same as in the stratosphere. What is the effect of this reaction on tropospheric ozone? 3.What’s the maximum number of O 3 that can be produced from the oxidation of 1 CH 4 ?

17. Tropospheric NO x Sources (Tg N yr -1 ) FOSSIL FUEL 23.1 AIRCRAFT 0.5 BIOFUEL 2.2 BIOMASS BURNING 5.2 SOILS 5.1 LIGHTNING 5.8 STRATOSPHERE 0.2 Probably bigger according to recent UW ATMSCI research

18. Tropospheric NO 2 from Space Martin et al. [2002] NO x Lifetime < 1 day! Fraction transported away from source regions very low

19. Lightning Flashes From Space DJF JJA

20. Long-Range Transport of NO x By NO x Reservoir: Peroxyacetyl Nitrate (PAN)

21. HO 2 NO 2 RO 2 NO 2 NO h O3O3 NO 2 HO 2 RO 2 HO RO CO RH CO 2 NO x Sources in Remote Regions

22. Questions 1.How would you calculate the chemical lifetime of NO x ? 2.Sketch a typical vertical profile for NO x. 3.Anthropogenic activity has lead to the increase of NO x, CO, and CH 4 emissions, with roughly factors of 2-4 increases of each over pre-industrial times. How have these changes affected OH concentrations?

23. [OH] global ~ constant CO and CH 4 tend to decrease OH NO x and O 3 tend to increase OH Predicted Change Since Pre-Industrial Times

24. Global Distribution of Ozone January August What are the main controls on tropospheric O 3 ?

25. O3O3 O3O3 Stratosphere 400-1100 Tg yr -1 Flux from Stratosphere 3400-5700 Tg yr -1 o Troposphere Chemical Production During NO x /HO x catalyzed photo-oxidation of CO, CH 4 500-1500 Tg yr -1 Deposition Chemical Loss HO x catalyzed destruction O( 1 D) + H 2 O 3000-4200 Tg yr -1 Global Tropospheric O 3 Budget