Chemical Reactivity of alpha-Pinene-derived Products in the Aqueous Phase: Implications on the Fate of Organic Nitrates

Abstract:

The production of organic nitrates has significant atmospheric importance due to the impact on regional air quality by influencing NO_x lifetimes and ozone formation. Additionally, these low volatility compounds readily partition into the particle phase and are important contributors to secondary organic aerosol. Once in the aerosol phase, organic nitrates undergo further chemical reactions that govern their fate in the atmosphere and, consequently, their impact on air quality. Recent research indicates that the presence of water on aerosol particles has a major impact on the reactivity of organic nitrates and that condensed phase hydrolysis leads to the destruction of organic nitrate species, depending on structure. Despite this knowledge, the chemical mechanisms, products, product reactivity and volatility are still uncertain, negatively impacting our understanding of aerosol phase processing and the contribution to air quality. To further understand the atmospheric impact of aerosol phase hydrolysis, we analyzed both condensed phase hydrolysis reactions involving alpha-pinene-derived standards and alpha-pinene photochemical chamber reaction filter samples, using a suite of spectroscopic and mass spectrometric techniques. We were able to measure the pH-dependent hydrolysis rate constants for several types of organic nitrates and identify specific reaction products. The chemistry involved exhibits a strong dependence on pH, providing important mechanistic clues. The results of this study will significantly contribute to our knowledge of aerosol phase chemistry and the impact on regional air quality with respect to the fate of organic nitrate species.