Abstract
Exposure to air pollution is a leading global health risk. Secondary organic aerosol (SOA) constitute a large portion of ambient particulate matter (PM). In this study, the water-soluble oxidative potential (OP) determined by dithiothreitol (DTT) consumption and intracellular reactive oxygen and nitrogen species (ROS/RNS) production was measured for SOA generated from the photooxidation of naphthalene in the presence of iron sulfate and ammonium sulfate seed particles. The measured intrinsic OP varied for aerosol formed using different initial naphthalene concentrations, however, no trends were observed between OP and bulk aerosol composition or seed type. For all experiments, aerosol generated in the presence of iron-containing seed induced higher ROS/RNS production compared to that formed in the presence of inorganic seed. This effect was primarily attributed to differences in aerosol carbon oxidation state {boldsymbol{(}}{bar{{bf{O}}{bf{S}}}}_{{bf{c}}}{boldsymbol{)}}. In the presence of iron, radical concentrations are elevated via iron redox cycling, resulting in more oxidized species. An exponential trend was also observed between ROS/RNS and {boldsymbol{(}}{bar{{bf{O}}{bf{S}}}}_{{bf{c}}}{boldsymbol{)}} for all naphthalene SOA, regardless of seed type or aerosol formation condition. This may have important implications as aerosol have an atmospheric lifetime of a week, over which {boldsymbol{(}}{bar{{bf{O}}{bf{S}}}}_{{bf{c}}}{boldsymbol{)}} increases due to continued photochemical aging, potentially resulting in more toxic aerosol.
Highlights
Exposure to air pollution is a leading global health risk
Organic aerosol constitute a significant portion of ambient PM32,33, and multiple field studies have repeatedly shown that secondary organic aerosol (SOA, formed from the oxidation of volatile organic compounds in the atmosphere) often dominate over aerosol of primary origin, even in urban centers[33,34,35]
The presence of redox-active metals on Secondary organic aerosol (SOA) health effects have not been considered even though laboratory studies have shown that the presence of metal-containing seeds influences SOA formation and chemical composition[50,51,52,53], and these metals are readily emitted via various processes[22,54]
Summary
It should be noted that these estimated contributions are only simple approximations to provide perspective as concentration addition may not apply for cellular responses These results are interesting as pure iron sulfate seed induced relatively low ROS/RNS production compared to that induced by the collected samples (i.e., ROS/RNSFS ROS/RNSFS+SOA). The ROS/RNS response induced by these samples and the OSc calculated for each collection period are shown in Fig. 2 (opened markers) for comparison These values fall within the exponential trend observed between ROS/RNS and OSc for SOA generated from different initial hydrocarbon concentrations. This suggests that the proxy for aging (OSc) investigated in this study may be used to understand the potential health implications of aged particles for SOA from a single pure compound. The OSc ranges for various organic aerosol subtypes resolved from ambient data world-wide, less-oxidized oxygenated organic aerosol (LO-OOA) and more-oxidized OOA (MO-OOA), have been measured previously and are shaded in Fig. 2 to provide
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