摘要：Non-methane hydrocarbons (NMHCs, C2–C6) have been measured at the Pallas-Sodankylä GAW station since 1994. In 2010, evacuated stainless-steel-canister sampling was replaced by an in-situ gas chromatograph, and parallel measurements were conducted over the period of a year. Results were in good agreement for all other compounds except propene. NMHCs at Pallas show a typical seasonal variation, with the highest mixing ratios in winter and lowest in summer. Alkanes did not show any clear diurnal variation, but ethene had a maximum at midday or during the afternoon in summer. This indicated biogenic sources. i/n-Butane and n/i-pentane ratios were higher than those typically found in urban areas or in traffic emissions, indicating other sources than these (e.g. wood combustion or natural gas) having a strong effect on mixing ratios at Pallas. Trend analysis over twenty years of measurements indicated a significant decreasing trend only for ethyne, even though emissions of NMHCs in the European Union (EU) decreased by 50% during this period. No trend was found for ozone, either. This indicated that some other source areas than the EU must play a significant role at Pallas. This was confirmed by source area estimates, which showed that eastern Europe is the main source area for high mixing ratios at Pallas.
