Reactive oxygen species associated with water-soluble PM2.5 in the southeastern United States: spatiotemporal trends and source apportionment

摘要

We assess the potential of the water-soluble fraction of atmospheric fineaerosols in the southeastern United States to generate reactive oxygenspecies (ROS) and identify major ROS-associated emission sources.ROS-generation potential of particles was quantified by the dithiothreitol(DTT) assay and involved analysis of fine particulate matter (PM) extractedfrom high-volume quartz filters (23 h integrated samples) collected atvarious sites in different environmental settings in the southeast,including three urban-Atlanta sites, in addition to a rural site. Pairedsampling was conducted with one fixed site in Atlanta (Jefferson Street),representative of the urban environment, with the others rotating amongdifferent sites, for ~250 days between June 2012 andSeptember 2013 (=483). A simple linear regression between the DTTactivity and aerosol chemical components revealed strong associationsbetween PM ROS-generation potential and secondary organic aerosol (WSOC – water-soluble organic carbon) insummer, and biomass burning markers in winter. Redox-active metals were alsosomewhat correlated with the DTT activity, but mostly at urban and roadsidesites. Positive matrix factorization (PMF) was applied to apportion therelative contribution of various sources to the ROS-generation potential ofwater-soluble PM in urban Atlanta. PMF showed that vehicularemissions contribute uniformly throughout the year (12–25%), whilesecondary oxidation processes dominated the DTT activity in summer (46%)and biomass burning in winter (47%). Road dust was significant onlyduring drier periods (~12% in summer and fall). Sourceapportionment by chemical mass balance (CMB) was reasonably consistent withPMF, but with higher contribution from vehicular emissions (32%). Giventhe spatially large data set of PM sampled over an extended period, thestudy reconciles the results from previous work that showed only region- orseason-specific aerosol components or sources contributing to PM ROSactivity, possibly due to smaller sample sizes. The ubiquitous nature of themajor sources of PM-associated ROS suggests widespread population exposuresto aerosol components that have the ability to catalyze the production ofoxidants in vivo.