Alkyl nitrates and secondary organic aerosol (SOA) produced during the oxidation of isoprene by nitrate radicals has been observed in the SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber) chamber. A 16 h dark experiment was conducted with temperatures at 289-301K, and maximum concentrations of 11 ppb isoprene, 62.4 ppb O3 and 31.1 ppb NO x. We find the yield of nitrates is 70±8% from the isoprene + NO3 reaction, and the yield for secondary dinitrates produced in the reaction of primary isoprene nitrates with NO3 is 40±20%. We find an effective rate constant for reaction of NO3 with the group of first generation oxidation products to be 7×10-14 molecule-1 cm3 s-1. At the low total organic aerosol concentration in the chamber (max=0.52 μgm-3) we observed a mass yield (ΔSOA mass/Δisoprene mass) of 2% for the entire 16 h experiment. However a comparison of the timing of the observed SOA production to a box model simulation of first and second generation oxidation products shows that the yield from the first generation products was <0.7% while the further oxidation of the initial products leads to a yield of 14% (defined as ΔSOA/Δisoprene2x where Δisoprene2x is the mass of isoprene which reacted twice with NO3). The SOA yield of 14% is consistent with equilibrium partitioning of highly functionalized C 5 products of isoprene oxidation.
CITATION STYLE
Rollins, A. W., Kiendler-Scharr, A., Fry, J. L., Brauers, T., Brown, S. S., Dorn, H. P., … Cohen, R. C. (2009). Isoprene oxidation by nitrate radical: Alkyl nitrate and secondary organic aerosol yields. Atmospheric Chemistry and Physics, 9(18), 6685–6703. https://doi.org/10.5194/acp-9-6685-2009
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