Dehydration of cyclic hemiacetals in particles formed by OH radical-initiated reactions of alkanes and alkenes has been shown to be catalyzed by nitric acid (HNO3). This reaction forms unsaturated dihydrofurans, which can evaporate from particles and react with OH radicals, O3, or NO3 radicals to form a variety of multifunctional products that can potentially form secondary organic aerosol (SOA). In order to quantify the effects of HNO3 on the rate of dehydration of cyclic hemiacetals, a series of environmental chamber experiments were conducted in which particulate cyclic hemiacetals were formed from the OH radical-initiated reaction of n-pentadecane in the absence of NOx and exposed to a range of concentrations of HNO3. A particle beam mass spectrometer was used to monitor the rapid formation and much slower decay of cyclic hemiacetals in real-time, with wall loss accounted for using the decay of DOS signal. HNO3 was measured using ion chromatography to analyze water extracts of particles sampled onto filters and gas sampled through an impinger. Dehydration rate constants increased linearly at 0.07 ± 0.00, 0.11 ± 0.00, 0.25 ± 0.01, and 0.57 ± 0.02 per h-1 for 0.25, 0.5, 1.0, and 2.0 ppmv of gas-phase HNO3, respectively, with HNO3 concentration, as expected for an acid-catalyzed reaction, and the amount of HNO3 measured in SOA particles was proportional to the gas-phase concentration of HNO3 and the SOA mass concentration, which allowed for an estimate of the Henry’s law constant of 3.3 x 104 M atm-1 for HNO3 in SOA particles. These two quantities can be used to model the behavior of cyclic hemiacetals in dry SOA particles as well as concentrations of HNO3.

Kinetics of acid-catalyzed dehydration of aerosol cyclic hemiacetals formed from the OH radical-initiated reaction of n-pentadecane

249th National Meeting (2015)

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Kinetics of acid-catalyzed dehydration of aerosol cyclic hemiacetals formed from the OH radical-initiated reaction of n-pentadecane<br />