A study of nighttime NO3 chemistry by differential optical absorption spectroscopy

In this paper, a newly constructed DOAS is described. The instrument was specially designed for making automated measurements over diurnal cycles in relatively clean environments, and has been employed since 1989 to measure NO3, NO2, O3 and CH2O. A comparative study of NO3 chemistry in two very different environments is presented. The first study took place in the marine boundary layer over Biscayne Bay in South Florida during 1989. Of particular interest was to determine the importance of dimethyl sulfide (DMS) as a sink for NxOy, through its rapid reaction with NO3. Modelling the observations indicates that in the clean marine boundary layer, ([NO2] ≤ 2 ppb), DMS accounts for up to about 50% removal of NxOy, whereas in more polluted conditions ([NO2] ∼ 25 ppb), DMS only removes about 10%. The other significant sink is probably adsorption of N2O5 onto moist aerosol surfaces. The second study took place near Edison, California, as part of the San Joaquin Valley Air Quality Study. At this dry and polluted location, NO3 exhibits marked variability during the night, although rarely exceeding 80 ppt. The presence of very high levels of industrial and agricultural hydrocarbons appears to limit both the maximum concentration and the duration of significant levels of NO3