Biomass burning as an important source of reactive oxygen species associated with the atmospheric aerosols in Southeastern United States – Implications for health effects of ambient particulate matter

Abstract:

We assessed the potential of water-soluble fraction of atmospheric fine aerosols in the southeastern US to generate reactive oxygen species (ROS). ROS-generation potential of particles was quantified by the dithiothreitol (DTT) assay and involved analysis of fine particulate matter (PM) extracted from high-volume quartz filters (23 h integrated daily samples) collected for one year at various sites in different environmental settings in the southeast, including three urban Atlanta sites, and one rural site in Yorkville. Water-soluble PM extracts were further separated into the hydrophobic and hydrophilic fractions using a C-18 column, and both fractions were analyzed for the DTT activity. Organic aerosol (OA) composition was measured at selected sites using a High-Resolution Time-of-Flight Aerosol Mass Spectrophotometer (HR-ToF-AMS). The various factors of the organic aerosols, i.e. Isoprene OA (Isop-OA), hydrocarbon-like OA (HOA), less-oxidized oxygenated OA, (LO-OOA), more-oxidized OOA (MO-OOA), cooking OA (COA), and biomass burning OA (BBOA) were also resolved, and their ability to generate ROS investigated by linear regression techniques.

Among all OA factors, BBOA was most consistently associated with ROS, with the highest intrinsic DTT activity of 151±20 pmol/min/μg. The water-soluble bioavailable fraction of BBOA-DTT activity is 2-3 times higher than the reported total-DTT activity of diesel exhaust particles. The total contribution of various aerosol sources to the ROS generating potential was also determined by the positive matrix factorization approach. Interestingly, biomass burning appears as the strongest source of ROS generation, with its annual contribution of 35 % to DTT activity; the contribution was higher in winter (47 %), than summer (24 %) and fall (17 %) seasons. The good agreement between the hydrophobic DTT activity with that estimated from the summed OA components, indicates that humic-like substances (HULIS), which are abundantly emitted in biomass burning is the most important class of organic compounds associated with ROS-generation. Collectively, these results imply that biomass burning emissions is a potentially serious health hazard, as they tend to be widespread, unregulated and likely to rise in future.