Abstract
Abstract. We assess the potential of the water-soluble fraction of atmospheric fine aerosols in the southeastern United States to generate reactive oxygen species (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) extracted from high-volume quartz filters (23 h integrated samples) collected at various sites in different environmental settings in the southeast, including three urban-Atlanta sites, in addition to a rural site. Paired sampling was conducted with one fixed site in Atlanta (Jefferson Street), representative of the urban environment, with the others rotating among different sites, for ~250 days between June 2012 and September 2013 (N=483). A simple linear regression between the DTT activity and aerosol chemical components revealed strong associations between PM ROS-generation potential and secondary organic aerosol (WSOC – water-soluble organic carbon) in summer, and biomass burning markers in winter. Redox-active metals were also somewhat correlated with the DTT activity, but mostly at urban and roadside sites. Positive matrix factorization (PMF) was applied to apportion the relative contribution of various sources to the ROS-generation potential of water-soluble PM2.5 in urban Atlanta. PMF showed that vehicular emissions contribute uniformly throughout the year (12–25%), while secondary oxidation processes dominated the DTT activity in summer (46%) and biomass burning in winter (47%). Road dust was significant only during drier periods (~12% in summer and fall). Source apportionment by chemical mass balance (CMB) was reasonably consistent with PMF, but with higher contribution from vehicular emissions (32%). Given the spatially large data set of PM sampled over an extended period, the study reconciles the results from previous work that showed only region- or season-specific aerosol components or sources contributing to PM ROS activity, possibly due to smaller sample sizes. The ubiquitous nature of the major sources of PM-associated ROS suggests widespread population exposures to aerosol components that have the ability to catalyze the production of oxidants in vivo.
Highlights
It has been hypothesized that several oxidative mechanisms can arise simultaneously, leading to a cascade of events that results in high concentrations of reactive oxygen species (ROS) in vivo
The sampling plan for Southeastern Center for Air Pollution and Epidemiology (SCAPE) involved paired simultaneous measurements using two instrumented sites, one of which was fixed at the Jefferson Street SEARCH (Southeastern Aerosol Research and Characterization) site (Edgerton et al, 2005, 2006; Hansen et al, 2003), the other was rotated among three different satellite sites, i.e., Yorkville, Roadside Atlanta, and Georgia Tech, all in Georgia
More detailed analysis based on the improved source profiles recently developed by an ensemble approach (Balachandran et al, 2014) is underway and here we only present the study’s average results from the chemical mass balance (CMB) to compare and validate the Positive matrix factorization (PMF) analysis
Summary
Substantial research has been dedicated to understanding the mechanisms by which ambient particulate matter (PM) causes adverse health effects in humans (Hoek et al, 2002; Samet et al, 2000; Gauderman et al, 2007; Stayner et al, 1998; Riediker et al, 2004; Sun et al, 1984; Sagai et al, 1993; Donaldson et al, 1996, 1997, 2003; Li et al, 2003, 2009a; Delfino et al, 2013). ROS concentrations in excess of the antioxidant capacity to neutralize them leads to oxidizing other cellular components, which eventually translates into numerous health outcomes (Delfino et al, 2005; Li et al, 2009a; Peters et al, 2006)
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