Modeling the Impact of Climate Change on PM2.5 and Associated Mortality in the Presence of Climate Variability in the US, and Understanding its Seasonal Drivers

Fine particulate matter (PM2.5) is susceptible to influence from future climate change but noise from meteorological variability can confound the climate change signal on PM2.5. The impact of RCP8.5 climate change on US annual average PM2.5 in the 2050s is quantified at high resolution by carefully accounting for climate variability. A novel method combines global chemistry-climate ensemble simulations (GFDL-CM3 model) that define the broad PM2.5 distribution, with high resolution downscaling of selected medium and high PM2.5 years by regional meteorological and air quality models (WRF, CMAQ). Understanding where the selected years lie in the global model distribution, a fine scale average annual PM2.5 distribution is constructed for the present-day (2006-2020) and mid-century (2051-2065) in each 12 km grid cell. Monte Carlo sampling of the two distributions estimates climate change impacts on PM2.5 as probability distributions that represent climate variability.In Aim 1, 91% of the continental US is estimated to experience increased average PM2.5 concentrations (up to 1.5 µg/m3) under midcentury climate relative to today, with varying effects of climate variability (standard deviation: 0.1-1.0 µg/m3) across regions and cities. The annual PM2.5 increase is largest in the Ohio River Valley and the Southeast (~1 µg/m3) and low in the Western US.The underlying meteorological drivers of PM2.5 changes in Aim 1 are investigated by species and season in Aim 2. Temperature increase (1-3 degC regionally) is an important driver leading to large summer and autumn increases (0.1 - 0.9 µg/m3) in secondary organic PM2.5 that exceed the nitrate aerosol decrease (0.02 - 0.27 µg/m3) by volatilization. Changes in mixing height, wind speed and precipitation reinforce the temperature effects on PM2.5 in some seasons and regions (e.g. winter Denver).In Aim 3, a Health Impact Function is used to translate the PM2.5 distributions from Aim 1 to associated premature deaths, estimating 15,300 (11,000 – 19,500) PM2.5-related US deaths under 2050s climate change with unchanged 2015 population and baseline mortality rates. Higher deaths - 22,200 (15,900 - 28,200) – are projected for 2050 population conditions. Considering climate variability in studies of climate change impacts on PM2.5 and related health effects could benefit future air quality management.