Non-methane hydrocarbons in the Arctic boundary layer

C2–C7 non-methane hydrocarbons were measured in clean maritime boundary layer air at latitudes between 53°N and 81°N. Measurements were made as part of the Arctic ice and environmental variability cruise aboard RRS James Clark Ross using a high sensitivity automated gas chromatography system. The data were collected during summer 1999, a period of continuous Arctic sunlight. Hydrocarbons of anthropogenic origin were observed to decrease in concentration with increasing latitude, a combination of dispersion and extensive atmospheric chemical processing. At high latitudes, low boundary layer conditions were common and species of exclusively anthropogenic origin reached highly stable although non-zero values (e.g. acetylene 27.8±2.4 pptV). A number of hydrocarbons believed to be of oceanic origin showed wide variability in these regions of atmospheric boundary layer stability (average ethene=37.2±20.9 pptV), highlighting inhomogeneity in the ocean to atmosphere flux rates. Whilst substantial increases in biological activity and productivity in the marginal ice zone have been previously reported, no evidence for increased biogenic hydrocarbon emissions were observed during this cruise. Removal mechanisms for atmospheric hydrocarbons were generally dominated by OH chemistry. Under clean maritime conditions the observed iso-/n pentane and butane ratios were in good agreement with published sea-fluxes. Using the relative ratios of iso-/n-butane and iso-butane/propane, there was evidence of significant chlorine atom chemistry at these high latitudes.