Aqueous Reaction Mechanisms and Kinetics of Atmospherically Relevant Carbonyl Organonitrates and Organosulfates

Abstract

The reaction mechanisms and rate constants for the aqueous phase reactions of atmospherically relevant carbonyl organonitrates (ONs) and organosulfates (OSs) were determined via bulk kinetics experiments using nuclear magnetic resonance (NMR) spectroscopy. The OSs and the nonalpha carbonyl substituted ONs were found to exclusively undergo a hydrolysis mechanism which is like that previously found for monofunctional and alpha hydroxy substituted ONs and OSs. However, the nonalpha carbonyl-substituted ONs were also found to undergo hydrolysis via sulfate catalysis (in addition to the previously found Brønsted acid catalyzed pathway), which has not been previously reported for any ONs. The alpha carbonyl-substituted ONs were found to react predominantly according to the E_CO2 mechanism (via both Brønsted acid and sulfate catalyzed pathways) which has also not been previously reported for any atmospherically relevant ONs. Because the E_CO2 mechanism leads to alpha-substituted dicarbonyl compounds, this process could be a precursor to accretion reactions which are needed to explain low volatility ambient secondary organic aerosol (SOA). The kinetics data indicate that the Brønsted acid catalyzed pathways could be relevant for SOA with pH < 1, while the sulfate catalyzed pathways are predicted to be relevant for SOA well below efflorescence point for (NH₄)₂SO₄.