Refined grid regional modelling of acidic and mercury deposition over northeast us and the contribution of the new york power sector

Abstract

Current implementations of federal and state regulations have relied heavily on regional-scale photochemical models which, however, reflect outdated emissions and have a level of uncertainly due to the coarse grid resolution used in typical applications. The purpose of this study is to refine the 12 km grid resolution from recent assessments to a 4 km grid level in a novel application of the Community Multiscale Air Quality (CMAQ) modelling system on an annual timescale. The main incentive was to determine the total acidic and mercury deposition over New York State (NYS) and the contribution of the NYS power sector point sources. To that end, the latest available United States Environmental Protection Agency's (USEPA) National Emissions Inventory (NEI) for 2011 and Weather Research Forecast (WRF) simulated meteorological data were generated on the 4 km grid domain over the Northeastern United States centred on NYS. For mercury, emissions of the elemental, oxidized and particulate species were characterized for source categories to allow for species-dependent wet removal factors and dry deposition velocities. The results for mercury deposition indicate very low contributions from all NYS, but showed the importance of the oxidized Hg from both wet and dry components. The impacts of Hg emissions outside the modelling domain were found to clearly dominate total depositions in NYS. For acidic deposition, the wet component controlled for sulphate, while for total sulphur and nitrates, dry deposition had a significant contribution. For the NYS power sector, the only large contribution was due to dry deposition of SO2 for total sulphur. The projected total wet depositions of sulphate, nitrate and mercury compare very favourably with observed levels at National Atmospheric Deposition Program (NADP) sites.