Seasonal variations of C2-C4 nonmethane hydrocarbons and C1-C4 alkyl nitrates at the Summit research station in Greenland

Abstract

We report measurements of light (C2-C4) nonmethane hydrocarbons (NMHCs) and C1-C4 alkyl nitrates made at Summit, Greenland, over a full annual cycle (June 1997-1998). The remoteness of the Summit camp from industrial source regions resulted in trends of these trace gases that showed a clear seasonal variation with low variability. Variability (calculated as the percentage I-sigma deviation of a running 10-point mean) averaged 7-9% for ethane over the entire study. The shorter-lived species (ethyne, propane, and the butanes) exhibited variability from 12-20% in winter to 20-100% in summer. The best fit curve to the annual cycle of ethane is a sinusoidal oscillation, but each of the shorter-lived NMHCs exhibited flat periods of low concentrations during the summer months. The C2-C4 NMHCs peaked between 8 and 24 February, with the longer-lived NMHCs maximizing latest. These data were broadly consistent with literature values, confirming that high-latitude Northern Hemisphere (NH) emissions are similar year to year. Employing their linear fall accumulation rates, we calculated average NMHC ratios versus ethane of 0.59(±0.10):0.33(±0.05):0.26(±0.08 :0.14(±0.04) for propane, ethyne, n-butane, and i-butane, respectively. We suggest that these ratios represent useful quantities with which to compare averaged mid- and high-latitude NH emission ratios. We also report the first year-round observations of the seasonal cycle of light C1-C4 alkyl nitrates. Similar to the NMHCs, the seasonal trend of these gases shows primary dependence on transport to Summit during winter, and photochemical removal during summer. Unlike their parent NMHCs, alkyl nitrate concentrations did not asymptote to low levels during summer and they exhibited winter maxima later with decreasing photochemical lifetime.