Formic acid and acetic acid in the western Sierra Nevada, California

Abstract

This paper reports the results of measurements of formic and acetic acid at four sites located along the western slope of the Sierra Nevada and compares the results with those of earlier studies. Formic acid concentrations ranged from approximately 1 to 40 ppb; those of acetic acid ranged from approximately 0.5 to 13 ppb. Mean formic acid concentrations were 18 ppb at Tehachapi, located at the southern extremity of the range, and between 12 and 13 ppb at the three other sites. Mean acetic acid concentrations ranged from 3.9 ppb at Blodgett Experimental Forest, located at the northern extremity, to 8.0 ppb at Yosemite. Comparison with previous studies indicates that carboxylic acid levels measured in the Sierra Nevada are higher than those measured in past studies, and in many cases average concentrations of both formic and acetic acids observed during this study were greater than the previously reported maxima. Comparisons were also made to nitric acid concentrations measured at Yosemite and Giant Forest from October 1986 to September 1987. At Yosemite, annual nitric acid concentrations averaged 0.20 ppb during the day, and 0.06 ppb at night; and at Giant Forest, nitric acid averaged 0.17 ppb during the day, and 0.05 ppb at night. Thus, the high formic and acetic acid concentrations observed in this study suggest that carboxylic acid are major contributors to the overall flux of ambient acid deposition in the western Sierra Nevada. © 1993.