Efficient Formation of Organic Particles from Isoprene Oxidation by a New Pathway

Shilling, J. E., Pacific Northwest National Laboratory

Aerosol Processes

Aerosol Processes

Liu JM, EL D'Ambro, BH Lee, FD Lopez-Hilfiker, RA Zaveri, JC Rivera-Rios, FN Keutsch, S Iyer, T Kurten, ZF Zhang, A Gold, JD Surratt, JE Shilling, and JA Thornton. 2016. "Efficient Isoprene Secondary Organic Aerosol Formation from a Non-IEPOX Pathway." Environmental Science & Technology, 50(18), 10.1021/acs.est.6b01872.


Simplified reaction mechanism of ISOPOOH forming highly oxidized multifunctional dihydroperoxide products following the described ISOP(OOH)2 pathway.


Simplified reaction mechanism of ISOPOOH forming highly oxidized multifunctional dihydroperoxide products following the described ISOP(OOH)2 pathway.

Science

New research showed that photooxidation of isoprene, copiously emitted from many plants, forms organic aerosol more efficiently than previously believed. The study identified new compounds with real-time mass spectrometry (MS) techniques and proposed a new chemical mechanism to explain the compounds’ formation.

Impact

The results allow for an improved representation of secondary organic aerosol (SOA) formation in the preindustrial atmosphere or in pristine regions with limited anthropogenic impacts, and thus are crucial from a climate forcing perspective.

Summary

Isoprene has a profound effect upon atmospheric chemistry and composition. The atmospheric pathways by which isoprene converts to secondary organic aerosol (SOA) and how man-made pollutants affect this process are subjects of intense research because particles affect Earth’s climate and local air quality. Using the environmental chamber at Pacific Northwest National Laboratory, the scientific team measured SOA mass yields from photooxidation of isoprene that were factors of 2 or more higher than those typically used in coupled-chemistry climate models. SOA yield was initially constant with increasing nitric oxide (NO) concentrations, but then sharply decreased for input concentrations above 50 ppbv (particles per billion by volume). Online measurements of aerosol molecular composition showed that the fate of second-generation RO2 radicals (organic peroxy radicals) is key to understanding the efficient SOA formation and the NOx-dependent yields described here and in the literature. These insights suggest that a more complex representation of NOx-dependent SOA yields may be important for the accuracy of global models.