PEROXYPROPIONYL NITRATE AT A SOUTHERN CALIFORNIA MOUNTAIN FOREST SITE

Ambient levels of peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at one mountain forest site (Tanbark Flat, elevation 800 m in southern California's San Gabriel Mountains), during the period August 8-October 16, 1989. Peroxy-n-butyryl nitrate (PnBN) was tentatively identified from a combination of laboratory experiments and field observations. Average concentrations during the study period were 2.9 ppb for PAN, 0.75 ppb for PPN, and 0.05 ppb for PnBN. Highest concentrations measured were > 16 ppb for PAN, 5.1 ppb for PPN, and 0.6 ppb for PnBN. Diurnal and seasonal variations are discussed in terms of "horizontal" transport of polluted air to the mountains, "vertical" transport reflecting inversion strength and mixing height, and a possible contribution of biogenic hydrocarbons. PPN/PAN concentration ratios calculated from some 3000 paired measurements were linearly correlated, i.e., PPN/PAN = 0.280 +/- 0.001 (intercept = -0.073 +/- 0.002, R = 0.943). The PPN/PAN ratios are discussed in terms of formation and removal processes for PAN and PPN. Since PPN is 2-8 times more phytotoxic than PAN, PPN must be included in any realistic assessment of forest and crop damage by photochemical oxidants.