Evaluation of PM2.5 source regions over the Mississippi Gulf Coast using WRF/HYSPLIT modeling approach

Fine particulate matter P.M 2.5 formed by precursors such as SO2, NOX, VOCs organic and elemental carbon, trace metals etc. resulting largely from intense industrial operations and transportation activities are known to be responsible for serious respiratory health effects. Evaluation of source regions and assessment of extent of contribution of various sources in Gulf Coast region will be useful for implementation of regulatory and mitigation measures.

In this present study, output from the HYSPLIT atmospheric dispersion model driven by the WRF (Weather Research Forecast) model is taken as a tool to assess the source location, transportation trends and extent of contribution to P.M2.5 using meteorological and air pollution (PM2.5 sulfate) observations that were collected under a joint JSU/TLGVRC-NOAA/ARL summer field experiment-2009 over the Gulfport area, at two locations: Harrison Central High School, and Wiggins/Stone County Airport.

The WRF model was used to simulate the meteorological parameters at high resolution of 4 km, which play an important role in air pollution dispersion. The model was designed to have three two-way interactive nested domains with the horizontal resolutions of 36, 12 and 4 km and the inner most domain covering the area of Gulf Coast region. The vertical resolution of the model was taken as 43 levels, of which 33 levels were confined to below 500 hPa so as to simulate the boundary layer flow characteristics. The model is integrated for 72 hours starting from 00UTC of 16, 17 and 18 June 2009 and the initial and boundary conditions are adopted from NCEP FNL data available at 1 degree horizontal resolution. The model derived meteorological fields were validated with the special observations collected at the two particular locations.

HYSPLIT model was integrated with the WRF-model derived meteorological fields to identify the source location using backward trajectory analysis. The backward trajectories are plotted for every 1 hour with different heights of mixed layer depths. Backward trajectories were plotted for a 24-hour period starting from observations at two sites and cluster analysis method was used to estimate the probable contribution from each source. As a second step, forward trajectories were plotted with different identified source locations using data of observations of P.M2.5 at known elevated point sources, and their concentration levels were calculated and compared with the observations collected over Harrison county public school and at Wiggin's airport to examine and assess possible relative contributions from different sources.