Influence of Global Change on Regional Air Quality in the Pacific Northwest and Northern Midwest Regions

Global climate change, land use changes and population growth are interrelated forces that can cause significant changes in future air quality in the US. In this work we address the consequences of global climate change for air quality in the continental US, with a specific focus on the Pacific Northwest and Northern Midwest regions. To do this, we employ a multi-scale numerical modeling system, which is comprised of global scale and nested regional models. On the global scale we employ the NCAR/DOE Parallel Climate Model (PCM) and the NCAR MOZART chemical transport model. The MM5/SMOKE/CMAQ regional modeling system is used to refine the global scale model outputs to simulate continental and regional scale air quality.

Global and regional scale simulations are conducted for a future period (2045 – 2055) based on predicted climatology and emissions and compared to base case simulations of a contemporary climate realization (1990 – 2000). For the contemporary simulations, US anthropogenic emissions are based on the National Emissions trend 1999 (NEI99) dataset, while future year anthropogenic emissions are projected using emission growth factors from EPA's the Economic Growth Analysis System (EGAS) along with the IPCC A2 “business as usual” scenario. Biogenic emissions are treated using the new biogenic emissions Model of Emissions of Gases and Aerosols from Nature (MEGAN). In addition, a newly developed Stochastic Fire Scenario Builder (FSB) is implemented to estimate prescribed and wild land fire emissions for the current and future scenarios. In this paper, we present an analysis of the results of contemporary and future, long term air quality simulations as a result of changes in global and regional climatology. As a way of qualifying our modeling results, air quality simulations for the contemporary period are compared with long term observations in the Pacific Northwest and Northern Midwest regions.