Modeling ozone and aerosol formation and transport in the Pacific Northwest and calculating fractional source contributions to downwind receptors

Two aspects of air quality modeling have been covered in this work; investigating the formation and transport of trace gases in our atmosphere and determining the upwind sources responsible for pollutants observed at a specific location. The results of ozone simulations from two Eulerian grid modeling systems (CALGRID and CMAQ) were compared with each other using the novel concept of process analysis. The models were found to yield similar solutions but arrive at these similar results by very different means. The CALGRID chemistry was “hotter” and exhibited greater peaks and valleys while the CMAQ advection processes were more dynamic than in CALGRID and moved larger quantities of ozone through a grid cell. CMAQ was next employed to model aerosol formation and transport in the Pacific Northwest. Two emission inventories (EI) were prepared, one based upon the EPA National Emission Trends 1996 (NET96) database and the BEIS2 biogenic emissions model, and one developed from the “ground up” by the Northwest Regional Modeling Center (NWRMC) participants and the GLOBEIS biogenic emissions model. The NWRMC EI solution tended to over-predict particulate matter with aerodynamic diameters less than 2.5 μg/m3 (PM2.5) with a normalized bias of 93% while the NET96 EI solution slightly under-predicted PM2.5 with a bias of −15%. Both CMAQ El solutions performed well for PM10 with normalized gross errors of approximately 50%.; A novel approach was developed relying on readily available models (MM5 and CALPUFF) to determine the upwind source area (the source-footprint) responsible for a downwind pollutant concentration. By running CALPUFF with an inverted wind field, plume dispersion theory was applied along a back-trajectory. This represents an improvement over traditional back-trajectory methods because turbulent diffusion was accounted for. The source-footprint was then combined with an existing emission inventory. Results for Boston, MA indicate that on May 25, 1999, 92% of the pollutant emissions impacting Boston came from within a radius of 30 km and that over a five hour period emissions from Connecticut and Rhode Island also influenced the Boston area.