Abstract
Abstract. Gas–particle partitioning and hydrolysis of organic nitrates (ON) influences their role as sinks and sources of NOx 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.
Highlights
Organic nitrates (ON) play an important role in atmospheric chemistry as they can act as sinks and sources of NOx (NO + NO2) and thereby affect the formation of tropospheric ozone and organic aerosol
All experiments were performed in the atmospheric physicochemical processes laboratory experiments (APPLE) chamber located at the University of Texas at Austin (UT-Austin)
When the UV lights are activated at time = 0, the NO immediately begins to react with qOH and other radicals to form NO2 and additional NOy compounds such as organic nitrates
Summary
Organic nitrates (ON) play an important role in atmospheric chemistry as they can act as sinks and sources of NOx (NO + NO2) and thereby affect the formation of tropospheric ozone and organic aerosol. Recent studies have suggested that organic nitrates in the condensed phase may undergo hydrolysis, leading to the formation of HNO3 (Day et al, 2010; Darer et al, 2011; Hu et al, 2011; Liu et al, 2012; Browne et al, 2013; Jacobs et al, 2014; Rindelaub et al, 2015). This is a more permanent sink for NOx and would decrease the regeneration of NOx from organic nitrates. Modeling organic nitrates and ozone formation depends on knowledge of the ON partitioning and hydrolysis rate
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