Peroxypropionyl nitrate at a southern California mountain forest site

Abstract

Ambient levels of peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at one mountain forest site, 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 pb 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 concentrations ratios calculated from some 3,000 paired measurements were linearly correlated, i.e., PPN/PAN = 0.280 {plus minus} 0.001 (intercept ={minus}0.073 {plus minus} 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.