1. VII. Tropospheric Ozone Catalytic Cycles Terminating the Cycles Initiating Organic Chemistry Meteorology

2. Ozone Damages lung – hard on kids, the aged, and anyone with bad lungs Concentrations 40-50 ppbv (continental background) 80 ppbv (EPA 8 hour limit) 120 ppbv (old EPA 1 hour limit)

3. EPA Map of Peak Ozone Concentration 0-60 ppb 61-79 ppb 80-99 ppb 100-110 ppb 111-124 ppb 125+ ppb No Data

4. Source of Ground-Level O 3 NO 2 + h → NO + O O + O 2 → O 3 NO + O 3 → NO 2 + O 2 NO x = NO + NO 2 NO x + sunlight yields O 3 These 3 reactions  steady state w/limited [O 3 ]

5. Add CO and HO x Chemistry OH + CO → H + CO 2 H + O 2 → HO 2 HO 2 + NO → OH + NO 2 NO 2 + h → NO + O O + O 2 → O 3 CO + 2 O 2 → CO 2 + O 3 CO CO 2 OH HO 2 NO NO 2 h O O3O3 O2O2

6. Add Organic Compounds… OH + CH 4 → CH 3 + HOH CH 3 + O 2 → CH 3 OO CH 3 OO + NO → CH 3 O + NO 2 CH 3 O + O 2 → CH 2 =O + HO 2 HO 2 + NO → OH + NO 2 2{NO 2 + h → NO + O} 2{O + O 2 → O 3 } CH 4 + 4 O 2 → CH 2 =O + 2 O 3 + H 2 O

7. NO x Concentrations Urban 5-20 ppbv Rural 0.1 – 5 ppbv Remote 0.005 -0.1 ppbv [HOO] ≈ Sum over [ROO] << [NO x ] except for Remote k(ROO + NO) ≈ k(HOO + NO) ≈ k(ROO + HOO) So HOO and ROO mostly react with NO

8. Termination of Cycles RO  RH + OH, O 2 → ROO  NO NO 2 h RONO 2 Limits NO x Cycling and organic radical chem.

9. Termination of Cycles at High [NO 2 ] NO 2 RCH 3 RCH=O OH HO 2 NO NO 2 h HONO 2 Stops HO x Cycling

10. Termination of Cycles at low [NO x ] RO  ROO  NO NO 2 h HOO  ROOH 2 HOO  → HOOH + O 2 organic radical chem. HOx cycling

11. Contour of Maximum [O 3 ] VOC (ppmC) NO x (ppb) [O 3 ] max 160 ppb 120 ppb 80 ppb NO x : VOC ≈ 1:7 downtown downwind

12. Fate of Organic Compounds- OH vacuum cleaner of the atmosphere OH + RH → R  + HOH OH + RCH=CH 2 → RCHCH 2 OH or RCH(OH)CH 2  OH Production photochemical (daylight) O( 1 D) + HOH → 2 OH HONO + h → OH + NO HOO + NO → OH + NO 2 HOO from CH 2 =O + h and organic radicals 

13. NO 3 + RCH=CH 2 → RCHCH 2 ONO 2 or RCH(ONO 2 )CH 2  NO 3 Production NO + O 3 → NO 2 + O 2 NO 2 + O 3 → NO 3 + O 2 (slower than NO 2 + h ) NO 2 + NO 3 → N 2 O 5 NO 3 + h → NO 2 + O or NO + O 2 (  = seconds) [NO 3 ] only significant in the dark !! Fate of Organic Compounds- NO 3 

14. Fate of Organic Compounds- O 3

15. Activity

16. Meteorology and Air Pollution “Dilution is the Solution to Pollution” Dispersing vs. Trapping pollutants Planetary Boundary Layer - region influenced by surface (convection) - vertical mixing time scale of 1 hour - 1st 100 m – 2 km - diurnal (daily) cycle

17. Planetary Boundary Layer 0422 0758 1324 1700 2037

18. Ozone and Topography

19. Topography and Meteorology Pacific Ocean(km)San Bernadino Mtns

20. Topography and Meteorology Pacific Ocean(km)San Bernadino Mtns

21. Topography and Meteorology

22. Inversion Layer Warmer above than below, so air is trapped time limited, specific geography

23. Key Points Sunlight, NO x, and Organics Cycles in HO x and NO x NO x is globally limiting reagent OH removes organics (O 3, NO 3 ) Kinetics calculations - steady state concentrations - fate of species Topography (meteorology)