Kinetics of NO 3 Uptake on Pyrene as a Representative Organic Aerosols

The uptake of NO3 on a pyrene coating at [NO3] = 2.5 × 1012–1.2 × 1013 cm−3 is studied using a coated-insert flow tube reactor coupled to a mass spectrometer. It is established that, in this concentration range, the uptake occurs by the impact recombination mechanism, whereas the consumption of surface sites involves the unimolecular decomposition of stabilized surface complexes. Several hundreds of NO3 radicals are consumed per surface site destroyed. The uptake coefficient depends on the exposure time, being described by the expression γ(t) = γ0exp(−t/τ), where γ0 and τ are parameters dependent on the NO3 concentration. Based on the Langmuir adsorption concept, the following elementary parameters determining the uptake process are estimated: the Langmuir coefficient, KL = 7.1 × 10−13 cm3; the desorption rate constant, kd = 44 s−1; and the rate constant for the unimolecular heterogeneous conversion of surface complexes, kr = 6.6 × 10−2 s−1. Gas chromatography–mass spectrometry measurements showed that the main products of the reaction are phthalates. The nitropyrene yield is found to be ~0.6%.