Characterizing Changes in Eastern US Pollution Events in a Warming World
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AbstractRisk assessments of air pollution impacts on human health and ecosystems would ideally consider a broad set of climate and emission scenarios, as well as natural internal climate variability. We analyze initial condition chemistryclimate ensembles to gauge the significance of greenhousegasinduced air pollution changes relative to internal climate variability, and consider response differences in two models. To quantify the effects of climate change on the frequency and duration of summertime regionalscale pollution episodes over the Eastern United States (EUS), we apply an Empirical Orthogonal Function (EOF) analysis to a 3member GFDLCM3 ensemble with prognostic ozone and aerosols and a 12member NCARCESM1 ensemble with prognostic aerosols under a 21st century RCP8.5 scenario with air pollutant emissions frozen in 2005. Correlations between GFDLCM3 principal components for ozone, PM2.5 and temperature represent spatiotemporal relationships discerned previously from observational analysis. Over the Northeast region, both models simulate summertime surface temperature increases of over 4C from 20062025 to 20812100 and PM2.5 of up to 14gm3. The ensemble average decadal incidence of upper quartile Northeast PM2.5 events lasting at least three days doubles in GFDLCM3 and increases by 50% in CESM1. In other EUS regions, intermodel differences in PM2.5 responses to climate change cannot be explained solely by internal climate variability. Our EOFbased approach anticipates future opportunities to datamine initial condition chemistryclimate model ensembles for probabilistic assessments of changing regionalscale pollution and heat event frequency and duration, while obviating the need to biascorrect concentrationbased thresholds separately in individual models.
