Particulate emissions from wheat and Kentucky bluegrass stubble burning in eastern Washington and northern Idaho

The PM2.5 emission factors (EF) in smoke from post-harvest wheat and Kentucky bluegrass (KBG) stubble burning were quantified in the United States Environmental Protection Agency test burn facility. The PM2.5 EFs from high and low combustion efficiency (CE) wheat burns were 0.8±0.4 and 4.7±0.4 g kg−1, respectively, and decreased with increasing CE. While these EFs are generally in agreement with literature, it is difficult to compare the PM2.5 EFs from KBG burns (12.1±1.4 g kg−1) due to the scarcity of published data. Wheat burns conducted with randomly piled stubble resulted in PM2.5 EFs different to those where the stubble was oriented as found in the field post harvest. Two separate methods for estimating EFs were employed and found to be in good agreement. The carbon in the biomass was almost quantitatively accounted for by measuring CO2, CO, total hydrocarbons (THC) and PM2.5 emissions. The PM2.5/CO emission ratios for wheat (0.05±0.01) agree with literature data, while the same ratio for KBG (0.23±0.02) was slightly higher than data reported. These ratios exhibit low dependence on CE and can be used to predict the level of one pollutant in a plume, when the concentration of the other is known. Wheat and KBG fields in 18 counties of eastern Washington and northern Idaho are burned on less than a tenth of the days of the year. Yet the fires were estimated to have produced between 0.04% and 34.5% of the total PM2.5 and CO emissions within the respective counties, during 2002.