O. Russell Bullock

Using a coupled lake model with WRF for dynamical downscaling

The Weather Research and Forecasting (WRF) model is used to downscale a coarse reanalysis (National Centers for Environmental Prediction–Department of Energy Atmospheric Model Intercomparison Project reanalysis, hereafter R2) as a proxy for a global climate model (GCM) to examine the consequences of using different methods for setting lake temperatures and ice on predicted 2 m temperature and precipitation in the Great Lakes region. A control simulation is performed where lake surface temperatures and ice coverage are interpolated from the GCM proxy. Because the R2 represents the five Great Lakes with only three grid points, ice formation is poorly represented, with large, deep lakes freezing abruptly. Unrealistic temperature gradients appear in areas where the coarse-scale fields have no inland water points nearby and lake temperatures on the finer grid are set using oceanic points from the GCM proxy. Using WRF coupled with the Freshwater Lake (FLake) model reduces errors in lake temperatures and significantly improves the timing and extent of ice coverage. Overall, WRF-FLake increases the accuracy of 2 m temperature compared to the control simulation where lake variables are interpolated from R2. However, the decreased error in FLake-simulated lake temperatures exacerbates an existing wet bias in monthly precipitation relative to the control run because the erroneously cool lake temperatures interpolated from R2 in the control run tend to suppress overactive precipitation.

Anthropogenic emission of mercury to the atmosphere in the northeast United States

The severity and spatial extent of the health impact of anthropogenic mercury (Hg) emission to the atmosphere depend on the emission rate and chemical form of the emitted species. The few measurements of combustion flue gas give highly variable results about how the emission is divided between the elemental (Hg°) and reactive forms and are difficult to extrapolate to a regional scale. Here we combine measurement of total gaseous mercury (TGM) and carbon dioxide (CO2) concentrations at a background site in the winter with carbon (C) emission inventory to show that at a regional (500 km) scale, the effective anthropogenic Hg° flux is 41(±2) g km−2yr−1 in the north-east United States. This regional-scale flux was higher under clear skies than under cloudy skies, suggesting some removal of Hg° by cloud water, but the physical mechanisms of the removal are yet to be identified.

Chapter 2.2 Application of the CMAQ mercury model for U.S. EPA regulatory support

Abstract On March 15, 2005, the U.S. Environmental Protection Agency (EPA) issued its Clean Air Mercury Rule (CAMR) to permanently cap and reduce mercury emissions from coal-fired Electric Generating Units (EGUs). Part of the development of the CAMR involved simulations of atmospheric mercury emission, transport and deposition across a large part of North America using a special version of the Community Multi-scale Air Quality (CMAQ) model to assess the expected decrease in mercury deposition from various emission control options. CMAQ model simulations of a 2001 base case and a 2020 case with full implementation of the CAMR and the separate Clean Air Interstate Rule (CAIR) showed that mercury emissions from EGUs are expected to decrease by 48% by 2020. Emission reductions of 68% were shown for reactive gaseous mercury, the form of mercury most readily deposited from the atmosphere. Simulated wet deposition of atmospheric mercury for 2001 was compared to observations from the Mercury Deposition Network (MDN). The CMAQ modeling was able to resolve about 60% of the observed site-to-site variance. The modeling also showed that the reduction in mercury deposition expected by 2020 from the CAIR and CAMR is similar to that which would have been obtained by completely eliminating mercury emissions from EGUs in the U.S. in 2001. Most of the emission reductions from the CAMR are in the form of elemental mercury. The CMAQ modeling showed nearly all of these emissions were exported from the modeling domain. Thus, it is expected that the CAMR will result in a reduction of the transport of mercury to other parts of the world.

Poster 21 The North American mercury model inter-comparison Study (NAMMIS)

Abstract NAMMIS is an intercomparison of atmospheric Hg models with a focus on North America. Three regional-scale atmospheric Hg models are the prime subjects of the study: the Community Multi-scale Air Quality model (CMAQ) developed by NOAA and EPA, the Regional Modeling System for Aerosols and Deposition (REMSAD) developed by ICFI, and the Trace Element Analysis Model (TEAM) developed by AER. The models were run for the entire year of 2001 using the same initial and boundary condition data.