Loretta J. Mickley Harvard University

1. Interactions Between Air Quality and Climate Change over the Eastern United States: An Investigation of Climate Change in Our Own Backyard Loretta J. Mickley Harvard University Daniel J. Jacob, Eric M. Leibensperger, Amos P.K.A. Tai, Shiliang Wu Wildfires in Quebec the same day. Haze over Boston on May 31, 2010 EPA Science Forum, March 14, 2012

2. Our work focuses on interactions of short-lived gases and particles in the atmosphere and climate change. Lifetimes in atmospheric chemistry Centuries: SF6, some CFCs Decades: many greenhouse gases: CO2, N2O, . . . 9-10 years: CH4 (methane, precursor to ozone and greenhouse gas) Days-weeks: O3 (ozone), particulate matter (PM) Seconds: OH, NO Pollution over Hong Kong Air pollution over Hong Kong reached dangerous levels one of every eight days in 2009

3. Air pollution in the United States: Ozone and fine particulate matter (PM2.5) are the two main pollutants 75 ppb (8-h average) 15 mg m-3 (1-y av.) Millions of people living in areas in violation of the standards. Counties violating the EPA standards Ozone PM2.5

4. The greenhouse effect keeps the Earth warm. • Greenhouse Effect • Radiation from the earth’s surface is absorbed and re-emitted by clouds and greenhouse gases: CO2. . . • This process warms the earth. CO2 CO2 CO2 Change in CO2 since mid-1800s: 280 ppm to 390 ppm. IPCC, 2007

5. Observed trends in surface temperature, 1880-2011. Global mean temperature increase is ~0.5 oC since 1950s. Boston/ Logan Airport Record annual mean temperature Over Boston, we see lots of year-to-year variability, but a significant trend towards warming. NASA Goddard Institute for Space Studies

6. Climate models show that observed global warming trends cannot be explained without human influence. Observed trend Models with human activity. Models with just natural processes Observed trend IPCC, 2007

7. Basic working of climate models All climate models depend on basic physics to describe motions and thermodynamics of the atmosphere: E.g., vertical structure of pressure is described by hydrostatic equation Climate models also depend on parameterizations for many processes. E.g., microphysics of cloud droplet formation, vegetation processes. Output Climate model Input Physics + Parameterized processes Tilt of earth, geography, greenhouse gas content Weather + Climate

8. Simulations of future climate depend on the path of socio-economic development. Global mean surface temperature anomalies Different scenarios follow different socio-economic paths for developed and developing countries. A2 = heavy fossil fuel B1 = alternative fuels A1B = mix of fossil + alternative fuels IPCC 2007

9. What do climate models predict for future (2100) climate? Annual mean Winter Summer Temperature increases everywhere, especially at high latitudes. Annual mean Winter Summer Precipitation changes are more complicated. Precipitation will likely increase over high latitudes but decrease over low latitudes. In between, the trend is not clear! Much uncertainty in future precipitation. Christensen et al., 2007

10. How do particles affect regional climate?

11. Black carbon California fire plumes Pollution off U.S. east coast Particles affect solar radiation directly…and also indirectly by modifying cloud properties. Light-colored particles reflect sunlight and cool the earth’s surface. Aircraft contrails and cirrus over Europe cooler

12. 1950 1960 1970 1980 1990 2001 Clearing trend in particles over United States since 1980s suggests possible recent warming. Calculated trend in surface sulfate concentrations, 1950- 2001. Sequence shows increasing sulfate from 1950-1980, followed by a decline in recent years. Most of aerosol has already cleared by 2010. Comparison to observed sulfate concentrations shows good agreement. Leibensperger et al., 2011

13. Observed US surface temperature trend Contiguous US o C No trend between 1930 and 1980 Warming trend after 1980 Change in temperatures over 60 year period, 1930-1990 Is the U.S. “warming hole” a signature of cooling due to particles? GISTEMP [2010]

14. We can examine the influence of particles on regional climate using a climate model. Eastern US • US manmade particles can explain the “warming hole.” • Warming since 1990s can be attributed to reductions in particle sources. Model without US particles Standard model Observations Most of the warming from reducing particle sources has already been realized. Leibenspergeret al., 2012

15. How does climate change affect smog episodes?

16. O2 Roles of ozone (O3) in the atmosphere. O3 EPA

17. Number of summer days with ozone exceedances, mean over sites in Northeast Days 1988, hottest on record Weather plays a large role in ozone air quality. A very hot summer can mean more ozone exceedances, even if emissions of ozone precursors are declining. Lin et al., 2001

18. In the Northeast, cold fronts sweep out pollution. • During heat wave: • Clear skies • Faster chemical reactions • Greater biogenic emissions • Little ventilation of pollutants Can climate change affect the frequency of cold fronts? Fewer cold fronts could mean more persistent smog episodes. Leibensperger et al., 2008

19. The number of cold fronts coming through the Northeast has already showed a signal of decline. Trend in summer low-pressure systems in S. Canada Trend in low-pressure systems and associated cold fronts is linked to rapid warming at high latitudes. What does this trend mean for ozone pollution in US? Emissions of ozone precursors have declined during this period. observations 0.14 /year model 0.16 /year with increasing GHGs model with constant GHGs Mickley et al., 2004; Leibensperger et al., 2008

20. Trend in emissions and trend in cold fronts have competing effects on surface ozone. Emissions Ozone Episodes Cold fronts per summer Ozone Episodes More heat waves, less ventilation, more persistent smog. Smog over Baltimore in 2002.

21. Observed trends of ozone pollution and cold fronts in Northeast US Number of ozone episode days (O3> 80 ppb) + Number of cold fronts, 1980-2006 Ozone episodes Cold fronts each summer Ozone episodes, constant climate Ozone exceedancedays in Northeast dropped from 30 in 1980 to 10 in 2006, but would have dropped to ≈ zero in the absence of cold-front trend. Leibensperger et al. [2008]

22. Most models agree that surface ozone will increase over the Northeast in a warming climate. Climate penalty for air quality: Harvard model shows 3-7 ppb increase in surface ozone in Midwest US in 2050s climate. During heatwaves, increases in ozone reach 10 ppb in future climate. Change in max daily 8-hour average JJA surface ozone in 2050s, relative to present-day. ppb Wu et al., 2008

23. Take home messages: Reductions in particles (PM2.5) over the Eastern US has likely contributed to rapid warming in recent years. Smog episodes in the East are sensitive to many meteorological variables, especially the frequency of cold fronts. The climate penalty: climate change will likely worsen ozone air quality over the East. Contiguous US Acknowledgments: o C Rapid warming after 1980

26. O2 Lifecycle of tropospheric ozone: production is viaoxidation of CO, VOCs, and methane in the presence of NOx. hn O3 STRATOSPHERE Many processes affected by climate 8-18 km TROPOSPHERE Soup of chemical reactions Ozone is produced in the atmosphere in sunlight. NOx O3 CH4 Deposition CO VOCs VOCs NOx NOx CO NOx VOCs NOx CH4 VOCs VOCs NOx emissions Biosphere Fires Human activity • Nonmethane volatile organic compounds (VOCs) • NOx = NO + NO2 26

27. . . . . . . Climate change affects many processes, including gas-particle partitioning. Life cycle of particulate matter (PM, aerosols) ultra-fine (<0.01 mm) fine (0.01-1 mm) cloud (1-100 mm) precursor gases nucleation cycling coagulation condensation Soup of chemical reactions coarse (1-10 mm) scavenging SO2 SO2 VOCs NOx NOx VOCs VOCs NOx NH3 VOCs NOx VOCs NOx combustion volcanoes agriculture biosphere soil dust sea salt wildfires combustion

28. Exceedances of the ozone air quality standard Current standard (75 ppb) EPA-recommended range for revision of standard (60-70 ppb)