The photochemical production of organic nitrates from α-pinene and loss via acid-dependent particle phase hydrolysis

The hydroxyl radical oxidation of α-pinene under high NO_x conditions was studied in a photochemical reaction chamber to investigate organic nitrate (RONO₂) production and fate between the gas and particle phases. We report an organic nitrate yield of 26±7% from the oxidation of this monoterpene in the presence of nitric oxide (NO). However, the apparent organic nitrate yield was found to be highly dependent on both chamber relative humidity (RH) and seed aerosol acidity, likely as a result of particle phase hydrolysis. The particle phase loss of organic nitrates is believed to increase the gas to particle partitioning within the system, leading to decreased RONO₂ yields in both the gas and particle phases at elevated RH and an apparent non-equilibrium partitioning mechanism. The hydrolysis of particle phase organic nitrates in this study, starting at low chamber relative humidity, implies that aerosol partitioning of organic nitrates may be an important sink for atmospheric NO_x and may have a significant impact on regional air quality.