Gas–particle partitioning and hydrolysis of organic nitrates formed from the oxidation of α -pinene in environmental chamber experiments

Gas–particle partitioning and hydrolysis of organic nitrates (ON) influences their role as sinks and sources of NO x and their effects on the formation of tropospheric ozone and organic aerosol (OA). In this work, organic nitrates were formed from the photo-oxidation of α -pinene in environmental chamber experiments under different conditions. Particle-phase ON hydrolysis rates, consistent with observed ON decay, exhibited a nonlinear dependence on relative humidity (RH): an ON decay rate of 2 day −1 was observed when the RH ranged between 20 and 60 %, and no significant ON decay was observed at RH lower than 20 %. In experiments when the highest observed RH exceeded the deliquescence RH of the ammonium sulfate seed aerosol, the particle-phase ON decay rate was as high as 7 day −1 and more variable. The ON gas–particle partitioning was dependent on total OA concentration and temperature, consistent with absorptive partitioning theory. In a volatility basis set, the ON partitioning was consistent with mass fractions of [0 0.11 0.03 0.86] at saturation mass concentrations ( C *) of [1 10 100 1000] µg m −3 .