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 Wildfires in Quebec the same day. Haze over Boston on May 31, 2010 Daniel J. Jacob, Eric M. Leibensperger, Amos P.K.A. Tai, Shiliang Wu EPA Science Forum, March 14,

2 Our work focuses on interactions of short-lived gases and particles in the atmosphere and climate change. Lifetimes in atmospheric chemistry Centuries: SF 6, some CFCs Decades: many greenhouse gases: CO 2, N 2 O, years: CH 4 (methane, precursor to ozone and greenhouse gas) Days-weeks: O 3 (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

Air pollution in the United States: Ozone and fine particulate matter (PM 2.5 ) are the two main pollutants 75 ppb (8-h average) 15  g m -3 (1-y av.) Ozone PM 2.5 Counties violating the EPA standards 3 Millions of people living in areas in violation of the standards.

The greenhouse effect keeps the Earth warm. IPCC, 2007 Greenhouse Effect Radiation from the earth’s surface is absorbed and re-emitted by clouds and greenhouse gases: CO 2... This process warms the earth. CO 2 4 Change in CO 2 since mid-1800s: 280 ppm to 390 ppm.

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

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

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. Tilt of earth, geography, greenhouse gas content Weather + Climate Input Physics + Parameterized processes Climate model Output

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

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

How do particles affect regional climate? 10

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

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

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

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

How does climate change affect smog episodes? 15

EPA Roles of ozone (O 3 ) in the atmosphere. O2O2 O3O3 16

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

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

The number of cold fronts coming through the Northeast has already showed a signal of decline. 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. Mickley et al., 2004; Leibensperger et al., 2008 Trend in summer low-pressure systems in S. Canada 0.14 /year 0.16 /year observations with increasing GHGs with constant GHGs model 19

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

Observed trends of ozone pollution and cold fronts in Northeast US Ozone exceedance days 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] Number of ozone episode days (O 3 > 80 ppb) + Number of cold fronts, Cold fronts each summer Ozone episodes Ozone episodes, constant climate 21

Change in max daily 8-hour average JJA surface ozone in 2050s, relative to present-day. 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. ppbWu et al.,

Take home messages: 1.Reductions in particles (PM2.5) over the Eastern US has likely contributed to rapid warming in recent years. 2.Smog episodes in the East are sensitive to many meteorological variables, especially the frequency of cold fronts. 3.The climate penalty: climate change will likely worsen ozone air quality over the East. Contiguous US o C Rapid warming after 1980 Acknowledgments: 23

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26 O3O3 O2O2 h O3O3 Deposition STRATOSPHERE TROPOSPHERE 8-18 km Lifecycle of tropospheric ozone: production is via oxidation of CO, VOCs, and methane in the presence of NOx. NOx Nonmethane volatile organic compounds (VOCs) NOx = NO + NO 2 Human activityFires Biosphere emissions Many processes affected by climate NOx VOCs NOx VOCs CO CH 4 Soup of chemical reactions Ozone is produced in the atmosphere in sunlight. 26

27 Life cycle of particulate matter (PM, aerosols) nucleation coagulation condensation wildfires combustion soil dust sea salt cycling ultra-fine (<0.01  m) fine (  m) cloud (1-100  m) combustion volcanoes agriculture biosphere coarse (1-10  m) scavenging precursor gases Climate change affects many processes, including gas- particle partitioning. Soup of chemical reactions NOx VOCs SO 2 NH 3 SO 2

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