Unexpectedly Efficient Secondary Organic Aerosol Formation from Isoprene Photo-oxidation

Description

With a global flux of ~500 Tg/year, emission of isoprene by vegetation is the largest source of non-methane hydrocarbons to the atmosphere, where its photochemical oxidation is a potentially substantial source of secondary organic aerosol (SOA) mass. The pathways by which isoprene converts to SOA, and how anthropogenic pollutants such as nitrogen oxides and sulfur affect this process, are a subject of intense research, in part because atmospheric particles profoundly affect Earth’s climate and local air quality. In the absence of nitrogen oxides and particle acidity, we measure SOA mass yields from isoprene photochemical oxidation of up to 25%, which are factors of 3, or more, higher than previously reported. Direct online measurements of aerosol molecular composition and the controlled addition of nitrogen oxides show that formation of di-hydroxy di-hydroperoxides is a key to such efficient SOA formation. These insights allow for improved quantitative estimates of SOA formation in the pre-industrial atmosphere and in biogenic-rich regions with limited anthropogenic impacts.