Formation and Stability of Atmospherically Relevant Isoprene-Derived Organosulfates and Organonitrates

• Published in: Environmental science & technology 2011-03, Vol.45 (5), p.1895-1902
• Main Authors: Darer, Adam I, Cole-Filipiak, Neil C, O’Connor, Alison E, Elrod, Matthew J
• Format: Article
• Language: English
• Subjects: Aerosols; Aerosols - analysis; Aerosols - chemistry; Air Pollutants - analysis; Air Pollutants - chemistry; Applied sciences; Aqueous chemistry; Atmosphere - chemistry; Butadienes - chemistry; Butylene Glycols - chemistry; Chemical compounds; Environmental Processes; Exact sciences and technology; Hemiterpenes - chemistry; Kinetics; Nitrates; Nitrates - analysis; Nitrates - chemistry; NMR; Nuclear magnetic resonance; Oxidation; Oxidation-Reduction; Pentanes - chemistry; Phase transitions; Pollution; Sulfuric Acid Esters - analysis; Sulfuric Acid Esters - chemistry
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es103797z

Isoprene is the precursor for number of alcohol, organosulfate, and organonitrate species observed in ambient secondary organic aerosol (SOA). Recent laboratory and field work has suggested that isoprene-derived epoxides may be crucial intermediates that can explain the existence of these compounds in SOA. To confirm this hypothesis, the specific hydroxy epoxides observed in gas phase isoprene photooxidation experiments (as well as several other related species) were synthesized and the bulk phase aqueous reactions of these species in the presence of sulfate and nitrate were studied via nuclear magnetic resonance (NMR) techniques. The results indicate that both primary and tertiary organosulfates and organonitrates are efficiently formed from the potential SOA reactions of isoprene-derived epoxides. However, the tertiary organonitrates are shown to undergo rapid nucleophilic substitution reactions (in which nitrate is substituted for by water or sulfate) over the whole range of SOA pH, while the tertiary organosulfates are found to undergo a much slower acid-dependent hydrolysis reaction. The primary organonitrates and organosulfates under study were found to be stable against nucleophilic substitution reactions, even at low pH. This finding provides a potential explanation for the fact that organosulfates are more commonly detected in ambient SOA than are organonitrates.