Oxidative potential of ambient water-soluble PM<sub>2.5</sub> in the southeastern United States: contrasts in sources and health associations between ascorbic acid (AA) and dithiothreitol (DTT) assays

Abstract

Abstract. The ability of certain components of particulate matter to induce oxidative stress through the generation of reactive oxygen species (ROS) in vivo may be one mechanism accounting for observed linkages between ambient aerosols and adverse health outcomes. A variety of assays have been used to measure this so-called aerosol oxidative potential. We developed a semi-automated system to quantify oxidative potential of filter aqueous extracts utilizing the dithiothreitol (DTT) assay and report here the development of a similar semi-automated system for the ascorbic acid (AA) assay. Approximately 500 PM2.5 filter samples collected in contrasting locations in the southeastern US were analyzed for a host of aerosol species, along with AA and DTT activities. We present a detailed contrast in findings from these two assays. Water-soluble AA activity was higher in summer and fall than in winter, with highest levels near heavily trafficked highways, whereas DTT activity was higher in winter compared to summer and fall and more spatially homogeneous. AA activity was nearly exclusively correlated with water-soluble Cu (r = 0.70–0.94 at most sites), whereas DTT activity was correlated with organic and metal species. Source apportionment models, positive matrix factorization (PMF) and a chemical mass balance method with ensemble-averaged source impact profiles (CMB-E), suggest a strong contribution from traffic emissions and secondary processes (e.g., organic aerosol oxidation or metals mobilization by secondary acids) to both AA and DTT activities in urban Atlanta. In contrast, biomass burning was a large source for DTT activity, but insignificant for AA. AA activity was not correlated with PM2.5 mass, while DTT activity co-varied strongly with mass (r = 0.49–0.86 across sites and seasons). Various linear models were developed to estimate AA and DTT activities for the central Atlanta Jefferson Street site, based on the CMB-E sources. The models were then used to estimate daily oxidative potential at this site over the 1998–2009 period. Time series epidemiological analyses were conducted to assess daily emergency department (ED) visits data for the five-county Atlanta metropolitan area based on the estimated 10-year backcast oxidative potential. Estimated AA activity was not statistically associated with any tested health outcome, while DTT activity was associated with ED visits for both asthma or wheeze and congestive heart failure. The findings point to the importance of both organic components and transition metals from biomass burning and mobile sources to adverse health outcomes in this region.

Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

“…The released OH radicals within particles or cloud droplets can oxidize other organic compounds, producing low-volatility products, including organic acids, peroxides and oligomers (Lim et al, 2010;McNeill et al, 2012;Ervens, 2015;Herrmann et al, 2015). Autoxidation in the condensed phase might be triggered by OH radicals forming highly oxidized compounds .…”

“…The DTT assay is based on the decay of DTT due to redox reactions with PM components, reporting the oxidative potential of PM in moles of DTT consumed per unit of time and mass of PM. Verma et al (2015a) and Fang et al (2016) reported that PM 2.5 sampled in an urban environment in Atlanta, Georgia, USA, has a DTT activity in the range of 10-70 pmol min −1 µg −1 . Assuming an integration time of 20 min needed for the extraction of PM in this work, this value corresponds to (1-8) ×10…”

“…It has been shown that semiquinones and reduced transition metals including, Fe(II) and Cu(I), can react with O 2 to form O − 2 , which can be further converted into H 2 O 2 (Gehling et al, 2014;Fang et al, 2016). Fenton-like reactions of H 2 O 2 with Fe(II) or Cu(I) can lead to the formation of OH radicals (Winterbourn, 2008;.…”

“…Ambient particles have been found to contain large amounts of ROS (mostly H 2 O 2 ) in the particle phase (Hung and Wang, 2001;Venkatachari et al, 2005Venkatachari et al, , 2007Fuller et al, 2014). Substantial amounts of particle-bound ROS are A. M. Arangio et al: Quantification of environmentally persistent free radicals and reactive oxygen species found on biogenic secondary organic aerosols (SOA) produced from the oxidation of α-pinene, linalool, and limonene (Chen and Hopke, 2010;Chen et al, 2011;Pavlovic and Hopke, 2011;Wang et al, 2011Wang et al, , 2012.…”

“…Oxidative stress is mediated by reactive oxygen species (ROS), including OH, H 2 O 2 and superoxide (O − 2 ), as well as organic radicals (Pryor et al, 1995;Winterbourn, 2008;Birben et al, 2012;. Upon PM deposition into the respiratory tract and interactions with lung antioxidants, H 2 O 2 can be generated by redox-active components contained in PM 2.5 such as transition metals (Charrier et al, 2014;Fang et al, 2016), semiquinones (Kumagai et al, 1997;Cho et al, 2005;McWhinney et al, 2013) and humic-like substances (Kumagai et al, 1997;Cho et al, 2005;Lin and Yu, 2011;Charrier et al, 2014;Dou et al, 2015;Fang et al, 2016;Verma et al, 2015a). H 2 O 2 can be converted into highly reactive OH radicals via Fenton-like reactions with iron and copper ions (Charrier et al, 2014;Enami et al, 2014).…”