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The Response of Surface Ozone to Climate Change over the Eastern United States
Pavan Nandan Racherla
Department of Engineering and Public Policy,
Carnegie Mellon University, Pittsburgh, PA
Peter J. Adams
Department of Engineering and Public Policy
Department of Civil and Environmental Engineering
Carnegie Mellon University, Pittsburgh, PA
| We examined the response of surface ozone to
future climate change over the eastern United States by performing simulations
corresponding to present (1990s) and future (2050s) climates using an
integrated model of global climate, tropospheric gas-phase chemistry,
and aerosols. A future climate has been imposed using ocean boundary conditions
corresponding to the IPCC SRES A2 scenario for the 2050s decade, resulting
in an increase in the global annual-average surface air temperature by
1.7°C, with a 1.4°C increase over the surface layer of the eastern
United States. Present-day anthropogenic emissions and CO2/CH4 mixing
ratios have been used in both simulations while climate-sensitive natural
emissions were allowed to vary with the simulated climate. There is practically
zero change in the spatiotemporally averaged ozone mixing ratios predicted
over the eastern United States. However, the severity and frequency of
ozone episodes over the eastern United States increased due to future
climate change, primarily as a result of increased ozone chemical production
due to increased natural isoprene emissions. The 95th percentile ozone
mixing ratio increased by 5 ppbv and the largest frequency increase occurred
in the 80-90 ppbv range. The most substantial and statistically significant
(p-value < 0.05) increases in episode frequency occurred over the Southeast
and Mid-Atlantic United States, largely as a result of 20% higher annual-average
natural isoprene emissions. Increased chemical production and shorter
average lifetime are consistent features of the predicted seasonal surface
ozone response, with the former’s magnitude for a location largely
a function of increased natural isoprene emissions, and the latter largely
due to faster dry deposition removal rates. Future climate change is also
predicted to lengthen the ozone season over the eastern United States
to include late spring and early fall. Significant interannual variability
is observed in the frequency of ozone episodes and we find that it is
necessary to utilize 5 years or more of simulation data in order to separate
the effects of interannual variability and climate change on ozone episodes.
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