Evaluating emission factors of PM(2.5), selected PAHs and phenols from wheat and Kentucky bluegrass stubble burning in eastern Washington and northern Idaho

In 2002, over 100,000 acres of wheat and 40,000 acres of KBG stubble were burned in 18 counties of eastern Washington (WA) and northern Idaho (ID), on less than a tenth of the days of the year. Emission factors (EFs) of pollutants from post-harvest agricultural burning are required to predict downwind impacts of smoke, to assess control strategies and to inventory emissions. EFs of several pollutants from wheat and Kentucky bluegrass (KBG) stubble burning were evaluated during laboratory scale burn experiments conducted in a US EPA test burn facility. The EFs from wheat stubble burning were: PM2.5 : 3.0+/-0.6 g kg-1; levoglucosan (LG): 150+/-130 mg kg-1; particulate elemental carbon (EC): 0.35+/-0.16 g kg-1; artifact corrected particulate organic carbon (OC): 1.9+/-1.1 g kg-1; CO: 53+/-8.0 g kg-1; total hydrocarbons (THC): 2.2+/-0.39 g kg-1; sum of 19 solid+ vapor phase polycyclic aromatic hydrocarbons (PAHs): 17+/-8.2 mg kg-1; sum of 19 solid+ vapor phase methoxyphenols (MPs): 79+/-36 mg kg-1. Combustion efficiencies (CE) of wheat burns ranged from 89-99%. For KBG, (CE range 82-96%) the EFs were: PM 2.5: 12+/-1.4 g kg-1; LG: 350+/-510 mg kg -1; EC: 0.63+/-0.056 g kg-1; OC: 6.9+/-0.85g kg-1; CO: 52+/-3.3 g kg-1; THC: 11+/-1.3 g kg-1; PAHs: 21+/-15 mg kg-1 and MPs: 35+/-24 mg kg-1. PM2.5, CO, THC, PAH, LG, OC and EC EFs from wheat are comparable to other similar studies reported in literature, but it is difficult to compare the KBG EFs due to the scarcity of published data. MP EFs appear more dependent on the stubble type, and are possibly linked to the lignin content therein. Using EFs found in this study, wheat and KBG burning was estimated to have produced between 0.04-34.5% of PM2.5 and CO emissions within the respective WA and ID counties, during 2002.; In general, when CE differences were taken into account, a reasonable degree of agreement was observed between EFs measured during field experiments, and those evaluated in the chamber. Ground based CO and CH4 measurements showed similar EF-CE relationships with samples collected on board a light aircraft. This highlights the need for evaluating CEs along with EFs, to facilitate proper interpretation.