Studies of NO3 Radical Reactions with Some Atmospheric Organic Compounds at Low Pressures

Article abstract of DOI:10.1021/j100340a015

Rate constantsfor the reactions of NO3 with trans-2-butene (1), isoprene (2), α-pinene (3), and acetaldehyde (4) have been measured as a function of temperature at low preessures in a fast flow system with LIF detection of the NO3 reractant and NO2 product.Rate costants for reaction 1 were found to be independent of pressure from 0.44 to 4.5 Torr, and the Arrhenius plot was curved.The data were fit by the four-parameter equation, k₁(T = 204-378 K) = (12.78 +/-0.36) x 1E-12 exp<-(530 +/- 100)/T + (1.28 +/- 0.26) x 1E-14 exp<(570 +/- 110)/T> (where all the error limits are the 95 percent confidence levels including a factor systematic error, and the units are cm³ molecule ^-1 s^-1).The data for isoprene were fit by a normal Arrhenius equation, k₂(T = 251-381 K) = (3.03 +/- 0.45) x 1E-12 exp<-(450 +/- 70)/T>.The Arrhenius plots for α-pinene and acetaldehyde were linear, and the fits gave k₃(T = 261-384 K) = (1.19 +/- 0.31) x 1E-12 exp<(490 +/- 70)/T> and k₄(T = 264-374 K) = (1.44 +/- 0.18) x 1E-12 exp<(-1860 +/- 300)/T>.The efficiencies for the conversion of NO3 to NO2 were determined for reactions of trans-2-butene and isoprene at low pressures and room temperature in He, N2, and O2 carrier gases, and at 360 K in 1 Torr of He.The measured yields of NO2 decreased with increasing size of the organic reactant, with increasing pressure, with decreasing temperature, and with increasing deactivation efficiency of the carrier gas.These observations and the temperature dependencies of the rate constants indicate that reactions 1-3 proceed by way of an addition mechanism.From the analysis used to determine the NO2 yields, NO2 fluorescence quenching rate constants were determined for isoprene, k = (3.5 +/- 1.1) x 1E-10, and trans-2-butene, k = (3.0 +/- 0.9) x 1E-10.