Isoprene-derived secondary organic aerosol (SOA), which comprise a large portion of atmospheric fine particulate matter (PM2.5), can be formed through various gaseous precursors, including isoprene epoxydiols (IEPOX), methacrylic acid epoxide (MAE), and isoprene hydroxyhydroperoxides (ISOPOOH). The composition of the isoprene-derived SOA affects its reactive oxygen species (ROS) generation potential and its ability to alter oxidative stress-related gene expression. In this study we assess effects of isoprene SOA derived solely from ISOPOOH oxidation on human bronchial epithelial cells by measuring the gene expression changes in 84 oxidative stress-related genes. In addition, the thiol reactivity of ISOPOOH-derived SOA was measured through the dithiothreitol (DTT) assay. Our findings show that ISOPOOH-derived SOA alter more oxidative-stress related genes than IEPOX-derived SOA but not as many as MAE-derived SOA on a mass basis exposure. More importantly, we found that the different types of SOA derived from the various gaseous precursors (MAE, IEPOX, and ISOPOOH) have unique contributions to changes in oxidative stress-related genes that do not total all gene expression changes seen in exposures to atmospherically relevant compositions of total isoprene-derived SOA mixtures. This study suggests that amongst the different types of known isoprene-derived SOA, MAE-derived SOA are the most potent inducer of oxidative stress-related gene changes but highlights the importance of considering isoprene-derived SOA as a total mixture for pollution controls and exposure studies. Environmental significanceIsoprene-derived secondary organic aerosol, which comprise a large portion of global fine particulate matter, has been linked to changes in inflammation and oxidative stress-related gene expression. The effects on expression of oxidative stress-related genes induced by SOA derived from two known isoprene photochemical oxidation products, IEPOX and MAE, have been previously studied but the effect on gene expression induced by SOA derived from the recently identified isoprene hydroxyhydroperoxide isomers (ISOPOOH) is unknown. The relative proportion of the three major known precursors of isoprene-derived SOA is dependent on the presence of anthropogenic emissions. Therefore, understanding the contribution by each component is important from a public health perspective as an initial step to improve health risk assessment for the purpose of developing emission control strategies to mitigate potential adverse effects.

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Arashiro, Maiko, Ying-Hsuan Lin, Zhenfa Zhang, Kenneth G. Sexton, Avram Gold, Ilona Jaspers, Rebecca C. Fry, and Jason D. Surratt. Effect of Secondary Organic Aerosol From Isoprenederived Hydroxyhydroperoxides on the Expression of Oxidative Stress Response Genes in Human Bronchial Epithelial Cells. Environmental Science: Processes & Impacts 20, no. 2 (2018): 332-339. https://pubs.rsc.org/en/content/articlelanding/2018/em/c7em00439g#!divAbstract