bstractThe formation of nitrous acid (HONO) in the dark from initial concentrations of N0 2 of 0.1-20 ppm in air, and the concurrent disappearance of N0 2 , were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300-and 5800-L volume (both with surface/volume ratios of 3.4 m' 1). In these environmental chambers the initial HONO formation rate was first order in the N0 2 concentration and increased with the water vapor concentration. However, the BONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-Qrder consumption rate of N0 2 was (2.8 :!: 1.2) x 10-4 min-1 in the 5800-L Tefion-coated evacuable chamber and (1.6 ± 0.5) x 10-4 min-1 in a 4300-L all·Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40-50% of the N0 2 reacted in the evacuable chamber and ca. 10-30% in the all-Tefton chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HN0 3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NO xorganic-air mixtures, and of HONO formation in polluted atmospheres. are discussed.
The nitrate radical, NO3, has been identified and measured for the first time in the polluted troposphere using long path (970 and 750 m) differential optical absorption spectroscopy at two sites in the Los Angeles basin. NO3 concentrations of up to 355 ppt were measured using the strong NO3 absorption bands at 623 and 662 nm. During pollution episodes from September 11 to September 19, 1979 concentrations increased sharply after sunset and peaked about one hour later at ∼ 20:00 (PDT). In many other cases peak concentrations were much lower and sometimes below the detection limit of several ppt. Possible sinks for the NO3 radical under polluted conditions are considered, including reaction with NO, reaction with organic species, and the hydrolysis of N2O5 for which a new upper limit rate constant is derived.
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