Reactive uptake of NO3 radicals by unsaturated fatty acid particles
. Physical Chemistry Chemical Physics 2011
The reactive uptake of NO3 by particles containing four unsaturated fatty acid species was studied for the first time in a flow tube reactor coupled to a chemical ionization mass spectrometer (CIMS). Using a mixed-phase relative rates technique, the reactive uptake coefficients, gpart, were determined to be (0.27 +/- 0.06) for oleic acid (OA), (0.53 +/- 0.12) for linoleic acid (LA), (0.72 +/- 0.17) for linolenic acid (LNA), and (1.01 +/- 0.18) for conjugated linoleic acid (CLA) in N2 bath gas. In the presence of 20% O2, their uptake coefficients are (0.31 +/- 0.09) for OA, (0.55 +/- 0.12) for LA, (0.78 +/- 0.17) for LNA, and (1.08 +/- 0.17) for CLA. All the uncertainties are 2s and represent precision only. The products of the NO3 reactions with these organic particles were studied in the presence and absence of O2 using CIMS. It was found that the detected yields and compositions of the products were substantially different with or without O2. Based on the observed products and general gas-phase chemistry of NO3 radicals, a reaction mechanism is proposed for NO3 reactions with unsaturated organic particles. The atmospheric implications of the heterogeneous chemical processes involving NO3 are also discussed.