World-wide ambient measurements of peroxyacetyl nitrate (PAN) and implications for plant injury

Abstract

Peroxyacetyl nitrate (PAN) is a major phytotoxic component of the photochemical oxidant complex in southern California, but its distribution and effects in other parts of the world are very poorly understood. Based on ambient air sampling at Riverside, California, in 1980, and published reports of PAN concentrations from other parts of the world, PAN concentrations in southern California appear to be five to ten times higher than those reported from eastern North America, western Europe, or Japan. PAN in Riverside, California, averaged 8.1 ppb in July, 9.4 ppb in September and 8.8 ppb in October 1980. These values represent the average of 48 measurements made at 15-min intervals between 0800 and 2000 LT. Potentially phytotoxic episodes, defined herein as PAN > 15 ppb for 4 h during the a.m. period or > 25 ppb for 4h in the p.m. period occurred 27 times in Riverside in 1980. These data were similar to PAN concentrations recorded in the mid 1960s in the Los Angeles Basin, indicating that PAN continues to be a serious air pollution problem in southern California. In contrast, PAN normally averages 1 ppb or less outside of southern California, and because of this low concentration, PAN by itself does not appear to be a major cause of photochemical oxidant injury to vegetation in those regions.