Air Quality Modeling for the Baltimore-Washington Area: Rigorous Science for Effective Policy

After decades of poor air quality (AQ), Baltimore, MD, and its neighbor Washington, DC are within striking distance of attaining the USEPA's standards for criteria pollutants including ozone. This results from the implementation of policies based on the best available science and on forecasts of air quality using the CMAQ model. Community-scale problems with black carbon (BC), coarse particles, and ultrafine particles (UFP) have received much less scrutiny and persist. We will discuss how measurements have helped constrain and improve chemical transport models and how effective communication with policy-makers has led to targeted emissions reductions. Examples include consideration of subgrid-scale sea and bay breezes that recirculate pollutants on hot summer days, how reservoirs such as organic nitrates extend the effective lifetime of NOx, and how aerosols and clouds alter photolysis rates. Combining observations and models has also helped quantify which, when, and where VOC controls can effectively reduce the rate of ozone formation in a regime, on average NOx-limited. Despite dramatic region-wide improvements in AQ, health and environmental problems continue on the community scale. These issues present new challenges for model resolution, and measurement coverage. We will discuss how new measurements and modeling capabilities attack the problems of over-nutrification of surface waters, and health and environmental justice impacts of short-lived pollutants BC, coal dust, and UFP.