Regional Chemical Transport Modeling to Assess Emissions Reduction Strategies in the Northeastern U.S.

The Northeast States for Coordinated Air Use Management (NESCAUM) works with a coalition of states in the northeast U.S. to better understand and improve their air quality. Our state members include Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont. NESCAUM also manages the Ozone Transport Commission (OTC), which is comprised of the eight NESCAUM states plus Delaware, the District of Columbia, Maryland, Pennsylvania, and Virginia. The OTC is a regional organization mandated by the 1990 Clean Air Act Amendments that is responsible for advising the Environmental Protection Agency (EPA) on ozone transport issues and for developing and implementing regional solutions to the ground-level ozone problem in the Northeast and Mid-Atlantic regions.

NESCAUM uses a variety of tools to perform technical and policy analysis, including the EPA’s Community Multi-scale Air Quality (CMAQ) model and output from the Comprehensive Air Quality Modeling with Extensions (CAMx). In one example, NESCAUM has been using CMAQ coupled with the Weather Research and Forecasting (WRF) meteorology model to investigate ozone production and sensitivity regimes based on data gathered during the Long Island Sound Tropospheric Ozone Study (LISTOS) beginning in 2018. Recent analysis combined work out of the OTC on high electric demand day (HEDD) electricity generating units (EGUs) with deep onroad vehicle emission reduction strategies to understand the relative effectiveness of HEDD reductions under very different atmospheric chemical regimes. Results indicate that after 90% emissions reductions of onroad vehicles—comparable to transportation sector electrification—the LISTOS region shifts to a more NO_X-sensitive regime, particularly in the New York City urban core. As a result, localized NO_X reductions from HEDD EGUs that otherwise would have less impact in a NO_X-saturated urban plume can contribute additional ozone reductions of up to 8 ppb on high ozone days. Because of deep NO_X reductions in transportation emissions, targeted measures on local sources with relatively smaller contributions to the overall NOx inventory can have larger benefits on ozone reductions. Ongoing modeling work continues to examine new and different approaches to improving air quality in the region by applying various emissions reduction strategies ranging from recently introduced regulatory strategies to long-term climate goals.