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

1. VII. Tropospheric OzoneCatalytic CyclesTerminating the CyclesInitiating Organic ChemistryMeteorology

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

4. Source of Ground-Level O3 NO2 + hn→ NO + O O + O2 → O3 NO + O3 → NO2 + O2 NOx = NO + NO2 NOx + sunlight yields O3 These 3 reactions  steady state w/limited [O3]

5. Add CO and HOx Chemistry OH + CO → H + CO2 H + O2 → HO2 HO2 + NO → OH + NO2 NO2 + hn → NO + O O + O2 → O3 CO + 2 O2 → CO2 + O3 CO OH NO2 hn NO HO2 CO2 O O3 O2

6. Add Organic Compounds… OH + CH4→ CH3 + HOH CH3 + O2 → CH3OO CH3OO + NO → CH3O + NO2 CH3O + O2 → CH2=O + HO2 HO2 + NO → OH + NO2 2{NO2 + hn → NO + O} 2{O + O2 → O3} CH4 + 4 O2 → CH2=O + 2 O3 + H2O

7. NOx Concentrations Urban 5-20 ppbv Rural 0.1 – 5 ppbv Remote 0.005 -0.1 ppbv [HOO] ≈ Sum over [ROO] << [NOx] 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 Limits NOx Cycling and organic radical chem. NO2 RONO2 hn NO RH + OH, O2→ ROO

9. Termination of Cycles at High [NO2] NO2 Stops HOx Cycling HONO2 RCH3 OH NO2 hn NO HO2 RCH=O

10. Termination of Cycles at low [NOx] RO organic radical chem. HOx cycling NO2 ROOH hn NO 2 HOO →HOOH + O2 HOO ROO

11. Contour of Maximum [O3] NOx : VOC ≈ 1:7 downtown NOx (ppb) [O3]max 160 ppb 120 ppb 80 ppb downwind VOC (ppmC)

12. Fate of Organic Compounds- OH vacuum cleaner of the atmosphere OH + RH → R + HOH OH + RCH=CH2 → RCHCH2OH or RCH(OH)CH2 OH Production photochemical (daylight) O(1D) + HOH → 2 OH HONO + hn → OH + NO HOO + NO → OH + NO2 HOO from CH2=O + hn and organic radicals 

13. Fate of Organic Compounds- NO3  NO3 + RCH=CH2 → RCHCH2ONO2 or RCH(ONO2)CH2 NO3 Production NO + O3 → NO2 + O2 NO2 + O3 → NO3 + O2 (slower than NO2 + hn) NO2 + NO3 → N2O5 NO3 + hn → NO2 + O or NO + O2 (t = seconds) [NO3] only significant in the dark !!

14. Fate of Organic Compounds- O3

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, NOx, and Organics • Cycles in HOx and NOx • NOx is globally limiting reagent • OH removes organics (O3, NO3) • Kinetics calculations • - steady state concentrations • - fate of species • Topography (meteorology)