Temperature dependence of the NO(3) absorption cross-section above 298 K and determination of the equilibrium constant for NO(3)+NO(2) <-> N(2)O(5) at atmospherically relevant conditions

The reaction NO(3) + NO(2) <-> N(2)O(5) was studied over the 278-323 K temperature range. Concentrations of NO3, N2O5, and NO2 were measured simultaneously in a 3- channel cavity ring- down spectrometer. Equilibrium constants were determined over atmospherically relevant concentration ranges of the three species in both synthetic samples in the laboratory and ambient air samples in the field. A fit to the laboratory data yielded Keq = (5: 1 +/- 0.8) x 10(-27) x e10871 +/- 46/T cm(3) molecule(-1). The temperature dependence of the NO3 absorption cross- section at 662 nm was investigated over the 298-388 K temperature range. The line width was found to be independent of temperature, in agreement with previous results. New data for the peak cross section ( 662.2 nm, vacuum wavelength) were combined with previous measurements in the 200 K-298 K region. A least- squares fit to the combined data gave sigma = [( 4.582 +/- 0.096) - ( 0.00796 +/- 0.00031) x T] x 10(17) cm(2) molecule(-1).