Non-methane hydrocarbons and carbonyls in the Lower Fraser Valley during PACIFIC 2001

Abstract

During August 2001, a field investigation was undertaken to determine the hydrocarbon and carbonyl loadings in the Lower Fraser Valley of British Columbia, Canada. Intensive ambient air sampling was carried out at sites representing urban and rural locales to identify and quantify atmospheric levels of non-methane hydrocarbon and carbonyl species. Results indicated that in the urban atmosphere (3-h) non-methane hydrocarbon levels exceeded 20 parts per billion (ppbv). Rural sites had lower levels of non-methane hydrocarbons. The dominant anthropogenic hydrocarbon species were propane, butane, 2-methylbutane and toluene. The most common biogenic hydrocarbons included isoprene, α-pinene, β-pinene and limonene. On average, biogenic hydrocarbons represented approximately 23% of the total hydrocarbon reactivity estimated for the airshed in the Lower Fraser Valley. Based on the hydroxyl radical-reactivity scale, limonene was determined to be the most photochemically relevant species at the urban site in the Lower Fraser Valley of British Columbia. Formaldehyde, acetaldehyde, and acetone were the dominant carbonyl compounds found in the Lower Fraser Valley. Three-hour averaged carbonyls levels reached 10 ppbv (3-h) and resulted from both direct emissions and hydrocarbon photooxidation. Atmospheric conditions strongly modulated the abundance of hydrocarbon and carbonyl compounds.