Agricultural burning smoke in eastern Washington—part I: Atmospheric characterization

Agricultural burning has been subject to intense debate in Eastern Washington. Rural communities are concerned about health impacts related to smoke exposure from field burning. However, the short-duration excursions of smoke often do not violate air quality standards at locations where air quality monitors are situated. The purpose of this study was to characterize the air quality in Pullman, WA during the fall 2002 prescribed field burning season, as part of a larger study conducted to examine community exposure to agricultural burning smoke and the related short-term health effects. Data collected included continuous PM2.5, PM10, CO2, nitrogen oxides, and 12-h integrated PM2.5, OC, EC, and levoglucosan (a biomass burning marker). Four episodes were defined when three consecutive 30-min PM2.5 averages exceeded 40 μg m−3. Two source-receptor models; the chemical mass balance model (CMB) and positive matrix factorization (PMF) were used to estimate smoke intrusion from regional agricultural burning. During this study, the average PM2.5, OC, and EC were similar during the daytime and nighttime, while LG was twice as high during the night. The CMB results showed major contributions of PM2.5 from soil (38%), vegetative burning (35%), and sulfate aerosol (20%), and much less from vehicles (2%) and cooking (1%). The 3-source profiles generated by PMF were consistent with those selected for CMB modeling. The PM2.5 estimates from these two models were highly correlated for individual sources. The LG, NOx, CO2, OC, and apportioned PM2.5 from vegetative burning and soil were higher during the episodes than during non-episode days, while EC and PM2.5 from secondary sulfate, vehicles, and cooking sources were similar throughout the study. We characterized the episodes of agricultural field burning with elevated LG, OC, and biomass burning contribution to PM2.5.