The effects of isoprene and NO x on secondary organic aerosols formed through reversible and irreversible uptake to aerosol water

El-Sayed, Marwa M. H.; Ortiz-Montalvo, Diana L.; Hennigan, Christopher J.

Isoprene oxidation produces water-soluble organic gases capable of partitioning to aerosol liquid water. The formation of secondary organic aerosols through such aqueous pathways (aqSOA) can take place either reversibly or irreversibly; however, the split between these fractions in the atmosphere is highly uncertain. The aim of this study was to characterize the reversibility of aqSOA formed from isoprene at a location in the eastern United States under substantial influence from both anthropogenic and biogenic emissions. The reversible and irreversible uptake of water-soluble organic gases to aerosol water was characterized in Baltimore, Maryland, USA, using measurements of particulate water-soluble organic carbon (WSOCinline-formulap) in alternating dry and ambient configurations. WSOCinline-formulap evaporation with drying was observed systematically throughout the late spring and summer, indicating reversible aqSOA formation during these times. We show through time lag analyses that WSOCinline-formulap concentrations, including the WSOCinline-formulap that evaporates with drying, peak 6 to 11 h after isoprene concentrations, with maxima at a time lag of 9 h. The absolute reversible aqSOA concentrations, as well as the relative amount of reversible aqSOA, increased with decreasing NOinline-formulaxinline-formula∕ isoprene ratios, suggesting that isoprene epoxydiol (IEPOX) or other low-NOinline-formulax oxidation products may be responsible for these effects. The observed relationships with NOinline-formulax and isoprene suggest that this process occurs widely in the atmosphere, and is likely more important in other locations characterized by higher isoprene and/or lower NOinline-formulax levels. This work underscores the importance of accounting for both reversible and irreversible uptake of isoprene oxidation products to aqueous particles.

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El-Sayed, Marwa M. H. / Ortiz-Montalvo, Diana L. / Hennigan, Christopher J.: The effects of isoprene and NOx on secondary organic aerosols formed through reversible and irreversible uptake to aerosol water. 2018. Copernicus Publications.

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