Air quality model evaluation data for organics. 3. Peroxyacetyl nitrate and peroxypropionyl nitrate in Los Angeles air

Ambient levels of peroxyacetyl nitrate [PAN, CH₃C(O)OONO₂] and peroxypropionyl nitrate [PPN, CH₃-CH₂C(O)OONO₂] have been measured during the 2-week period Aug 28-Sept 13, 1993, at four locations in the urban Los Angeles area. Highest concentrations recorded were 9.9 ppb for PAN and 1.5 ppb for PPN. Diurnal and spatial variations were consistent with photochemical production during eastward (inland) transport. Results for PAN are compared to those obtained in previous studies of ambient PAN in the urban Los Angeles area. Results for PPN, measured for the first time in the urban Los Angeles area, are compared to those recently obtained at southern California mountain sites and other locations. Ambient levels of PPN were correlated with those of PAN, with least squares linear regressions slopes (PPN vs PAN) of 0.153 ± 0.030 (Long Beach), 0.136 ± 0.026 (Los Angeles), 0.166 ± 0.018 (Azusa), and 0.097 ± 0.014 (Claremont). These ratios are compared to those measured previously at other locations and are briefly discussed with respect to spatial changes in the relative importance of those hydrocarbons that are precursors to PAN and PPN. The amount of PAN lost due to thermal decomposition was calculated and was comparable in magnitude to that measured.