Abstract View
Differences in Mass Yields and Composition of Secondary Organic Aerosols from Nitrate Radical Oxidation of Isoprene under Various Reaction Conditions
TIANCHANG XU, Masayuki Takeuchi, Yuchen Wang, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 442
Working Group: Aerosol Chemistry
Abstract
Isoprene is the most abundant biogenic volatile organic compounds in the atmosphere. The reaction of isoprene and nitrate radicals (NO3) at nighttime is important because of the high reactivity of NO3 with isoprene and the high yields of secondary organic aerosols (SOA). While SOA formation from isoprene and NO3 reaction has been investigated in previous studies, different SOA yields and product distributions were reported and the underlying reasons have not been fully examined and understood. Here, we conduct laboratory chamber experiments with isoprene and NO3 formed from N2O5 under various reaction conditions to examine their influences on SOA yields and composition. Experiments are conducted under different N2O5 to precursor ratios. Further, two different generation methods of N2O5 are employed: (1) pre-mixes NO2 and O3 in a flow tube before introduction into the chamber and (2) injects NO2 and O3 separately into the chamber. The chemical composition of gas- and particle-phase products is measured continuously using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Filter Inlet for Gases and AEROsols coupled to a High-Resolution Time-of-Flight Iodide Chemical Ionization Mass Spectrometer (FIGAERO-CIMS). We observe that SOA yields increase with increasing N2O5 to isoprene ratio. This is attributed to the formation of higher-generation products with lower volatility, since the reaction can proceed to a larger extent with higher oxidant exposure. The major higher-generation compounds detected in the particle phase include 2N-monomer C5H10N2O8, 3N-monomer C5H9N3O10, and 3N-dimers C10H17N3O12-13. We observe that the relative abundance of monomers and dimers changes with precursor to N2O5 ratios. Results from this study can offer a better understanding of isoprene nitrate and SOA formation in the atmosphere where the relative abundance of isoprene and oxidants vary.