Abstract View
Observations of Nitrate Radical Initiated Oxidation of Various Monoterpenes in a Laboratory Chamber Using NO3-CIMS
MICHELIA DAM, Danielle C. Draper, Andrey Marsavin, Juliane Fry, James Smith, University of California, Irvine
Abstract Number: 650
Working Group: Aerosol Chemistry
Abstract
Chemical ionization mass spectrometry with nitrate reagent ion (NO3-CIMS) was used to probe the composition of nitrate radical initiated monoterpene oxidation products in laboratory chamber experiments for four different monoterpene systems (a-pinene, b-pinene, d-carene, a-thujene). The major species in each system were distinctly different, showing the effect of monoterpene structure on the oxidation mechanism. By comparing groupings of products based on ratios of elements in the general formula CwHxNyOz, the dominance of specific mechanistic pathways (fragmentation, termination, radical rearrangement) were observed for each system. Additionally, the time series of the highly oxidized reaction products gives insight into the ratio of relative production and loss rates of these high molecular weight products. Measured effective O:C ratio of reaction products were anti-correlated to observed particle formation for each system. Monomer:dimer ratio of species did correlate, however. Gas phase yield of oxidation products measured by NO3-CIMS and total gas phase alkyl nitrate yield measured with a thermal dissociation cavity ring-down spectrometer (TDCRDS) corresponded to particle number measured with a scanning mobility particle sizer (SMPS) for each monoterpene system, with the exception of the a-thujene system, which produced a considerable concentration of low volatility products, but no particles. Speciated wall loss interactions were measured with NO3-CIMS and found to be highly variable among oxidized reaction products in our stainless steel chamber. The information gained from this detailed comparison of gas phase composition with currently established mechanisms provides additional insight into the NO3 radical initiated monoterpene oxidation process and further elucidates the effect of these species on particle formation and growth.