PEROXYACYL NITRATES AT SOUTHERN CALIFORNIA MOUNTAIN FOREST LOCATIONS

Ambient levels of the peroxyacyl nitrates [RC(O)OONO2] PAN (R = CH3) and PPN (R = C2H5) have been measured at two southern California mountain forest locations impacted by urban photochemical smog. The highest levels recorded were 22 ppb for PAN and 4.3 ppb for PPN; 24-h averages were 2-10 ppb for PAN and 0.25-1.7 ppb for PPN. PPN and PAN were highly correlated, with PPN/PAN ratios of 0.28 (August-October 1989), 0.18 (August-September 1990), and 0.14 and 0. 19 (August-September 1991). Diurnal and seasonal variations in PAN/ozone, PPN/ozone, and PPN/PAN ratios are discussed in terms of formation and removal processes for PAN and PPN. The relative contribution of olefins, aromatics, carbonyls, and paraffins to the observed PPN PAN ratios has been estimated. Other peroxyacyl nitrates measured included PnBN (R = n-C3H7), which was frequently observed at one location at levels of 0.2-0.4 ppb. With a detection limit of 0.2 ppb, the isoprene oxidation product MPAN [R = CH2 = C(CH3)] was only observed in a few instances at one location but was observed more frequently at the other at levels of 0.3-1.2 ppb.