Analysis of Transport and Three-Dimensional Distributions

The impact of pollutant transport on the air quality in a downwind airshed is a function of the precursor emissions in the upwind airshed, the formation of ozone or particulate matter along the transport path, the losses of pollutants by deposition and reaction along the transport path, the background pollutant and precursor concentrations, the meteorological phenomena that transport and mix the pollutants, and the local precursor emissions in the downwind basin. Depending upon the particular scenario, effective control strategies may require emission controls in the upwind airshed, the downwind airshed, or both. Grid modeling is ultimately needed in many situations to evaluate the relative effects of different control strategies. STI data analysts consider the following issues when analyzing pollutant transport: transport of ozone and PM and their precursors; emissions along a transport path; duration and temporal variability, e.g., same-day transport, overnight transport, and transported pollutants that remain overnight aloft in the receptor area (carry-over); and upper-air meteorological and air quality data.