Global atmospheric changes and future impacts on regional air quality

1. Global atmospheric changes and future impacts on regional air quality Will O3 produced elsewhere in the world affect local air quality? How will a changing climate affect surface O3 concentrations? Loretta J. Mickley Harvard University

2. Number of people living in US counties violating National Air Quality standards, 1999 Focus of talk

3. Good O3 vs Bad O3 NOx = nitrogen oxide radicals VOC = volatile organic carbon

4. How has tropospheric O3 increased in last 100 years? Ozone measured on various mountaintops in Europe, 1870 to 1990

5. What could increase regional O3 in 21st century? • Increase of local emissions of O3 precursors (NOx, VOCs) • Transport of O3 or O3 precursors produced elsewhere Can use model with observed winds to calculate current influence • Climate change effects on O3 loss and production rates Need to use model that generates its own climate (GCM)

6. How does intercontinental transport of O3 enhance local O3 surface concentrations today? North America Europe Asia GEOS-CHEM model, July 1997, Li et al 2002

7. How does N. American O3 affect O3 violations in Europe? Number of exceedance days for European standards (55 ppb, 8 hour average) Number of exceedance days due to North American sources GEOS-CHEM model, summer, Li et al 2002

8. Does Asian O3 enhance US surface O3 in summer? Subsidence of Asian pollution + production aloft Maximum Asian enhancements (up to 14 ppb) occur at intermediate ozone levels (50-70 ppb) Tropical air Stagnation Major concern if O3 standard decreases or Asian O3 increases Fiore et al. 2002

9. How important is methane to O3 and climate? Methane = overlooked precursor of ozone, has long lifetime (8-10 years) Cutting methane by 50% would: decrease incidence of ozone > 80 ppb in surface air by more than 50% decrease radiative forcing by both ozone and methane Trends in methane

10. O2 + hn Stratospheric ozone How might climate change affect O3 loss and production? ? Complex non-linear chemistry ? hn hn, H2O Nitrogen oxides (NOx) CO, Hydrocarbons ? Ozone (O3) Hydroxyl (OH) O3 source with high NOx O3 sink with low NOx physics chemistry biology Fires Biosphere Human activity Ocean

11. How might changing climate affect surface O3? Temperature changes ? (not the whole story!) Changes in circulation frequency of stagnation? stratospheric influx of ozone? transport from other continents? Lightning frequency? Water vapor concentrations? Emissions of VOCs from trees, grasses? Sum of climate changes more ozone? less ozone?

12. Chemistry, Aerosols, and Climate: Tropospheric Unified Simulation (CACTUS) Objective: to improve understanding of interactions between atmospheric chemistry, aerosols, and climate

13. Approach: coupled chemistry-aerosol-climate General Circulation Model (GCM) CACTUS model Atmospheric chemistry • emissions • land use • greenhouse gas GISS GCM Aerosol microphysics D climate • chemistry

14. CACTUS model study of preindustrial O3 Monthly mean observations at two sites in Europe Two model attempts, with differing natural emissions, but same climate as present-day Mickley et al. 2000

15. How will atmospheric motions change in 2xCO2 climate? • Stronger convective transport • Weaker interhemispheric exchange Use SF6 to show how atmospheric motions change with warmer climate Rind et al., 2001

16. How can we calculate change in O3 due to climate? • 2000-2100: change well-mixed greenhouse gases year-by-year, calculate D climate 2.2000,2025,2050,etc: change emissions of O3 precursors, use current climate, calculate D ozone • 2000,2025,2050,etc: recalculate D ozone using climate from step 1. Diagnose D in ozone due to climate change. (Step 3- Step2)

17. Final thoughts Transport could have a big effect in future if Asian emissions increase. We need to learn how climate change may affect local ozone levels Ozone in July 2100, worst case scenario