MEASUREMENT OF ISOPRENE AND ITS ATMOSPHERIC OXIDATION-PRODUCTS IN A CENTRAL PENNSYLVANIA DECIDUOUS FOREST

Ambient concentrations of isoprene and several of its atmospheric oxidation products - methacrolein, methylvinyl ketone, formaldehyde, formic acid, acetic acid, and pyruvic acid - were measured in a central Pennsylvania deciduous forest during the summer of 1988. Isoprene concentrations ranged from near zero at night to levels in excess of 30 ppbv during daylight hours. During fair weather periods, midday isoprene levels normally fell in the 5-10 ppbv range. Methacrolein and methylvinyl ketone levels ranged from less than 0.5 ppbv to greater than 3 ppbv with average midday concentrations in the 1 to 2 ppbv range. The diurnal behavior of formaldehyde paralleled that of isoprene with ambient concentrations lowest (approximately 1 ppbv) in the predawn hours and highest (> 9.0 ppbv) during the afternoon. The organic acids peaking during the midday period with average ambient concentration of 2.5, 2.0, and 0.05 ppbv for formic, acetic, and pyruvic acid, respectively. These data indicate that oxygenated organics comprise a large fraction of the total volatile organic carbon containing species present in rural, forested regions of the eastern United States. Consequently, these compounds need to be included in photochemical models that attempt to simulate oxidant behavior and/or atmospheric acidity in these forested regions.