Analysis of atmospheric hydrocarbons during winter MONEX

Abstract

The distribution of gaseous atmospheric hydrocarbon compounds, halocarbons, and nitrous oxide were studied. Whole air samples were collected aboard the NCAR Electra aircraft platform during the Monsoon Experiment (MONEX) flights in Kuala Lumpur, Malaysia, and on ferry flights to and from the United States. Foliage emission rates were also measured on some tropical plants.The average free tropospheric TNMHC (total non-methane hydrocarbon) levels from both the transit flight and mission flights were low (2.5 μg/m3). TNMHC just above the forest canopy over Borneo but within the mixing layer was higher and the concentrations over land were higher than those obtained over the ocean. The fluorocarbons showed a small latitude gradient or a difference between continental and oceanic air masses or (possibily) both. Methyl chloroform also showed a significant latitude profile. Nitrous oxide was uniformly distributed in the atmosphere. The C2 hydrocarbons, ethane and acetylene, also showed latitudinal gradients.The emission rates of foliage in the tropics were higher than those reported by other investigators for the mid-latitudes. The species sampled indicated that most tropical vegetation emits predominantly isoprene, rather than terpenes.