The 2000/2001 Missoula Valley PM sub(2.5) Chemical Mass Balance Study, Including the 2000 Wildfire Season Seasonal Source Apportionment

The 2000/2001 Missoula Valley PM sub(2.5) chemical mass balance (CMB) study was designed to evaluate the effect of air-pollution controls implemented in Montana. The PM sub(2.5) source contributions were determined throughout all four seasons using the updated CMB version 8.0 software. Thirty-five source profiles, which are tabulated, were used in the model to represent Missoula Valley sources, and CMB model runs were conducted for each of 31 sample days at both the urban Boyd Park and rural Frenchtown sites. At both sites, the sources contributing to the fine fraction were similar, with wood combustion identified as the main source. Residential wood burning was identified during the winter months, while slash and prescribed burns were identified during the spring and fall, and wildfires were identified during the summer. Diesel was identified as the next most important source, followed by ammonium nitrate, especially during the winter months. Other contributors identified included kraft recovery boilers from a local pulp mill, hog fuel boilers from the local wood products industry, and street sand.