Ten years of light hydrocarbons (C2–C6) concentration measurements in background air in Finland

Light hydrocarbons (C2–C6) have been measured at two background stations, Utö (EMEP station) and Pallas (GAW station), in Finland since 1994. Utö is a small, rocky island in the Baltic Sea southwest of the mainland and Pallas is located in Lapland. Canister samples were taken twice a week and analyzed in a laboratory using gas chromatography. Maximum concentrations are observed in winter due to the very limited amount of daylight and hence of hydroxyl radicals. During spring the concentrations start declining as more light becomes available, and for most of the compounds minimum concentrations are measured during summer. Concentrations are lower at Pallas than on Utö, indicating more aged air there. Only isoprene, ethene and propene have higher concentrations at Pallas, due to natural emissions. Higher concentrations are measured in air masses coming from Central Europe and Russia, whereas air masses coming from the North Sea and the Arctic are cleaner. During the ten years of measurements, the concentrations of ethyne, pentanes and hexanes have decreased by about 10–40%, although only few of these trends are significant. However, the compounds with long lifetimes (ethane and propane) show an increasing trend especially at Pallas. Butane concentrations are also increasing at Pallas. This can indicate an increase of the VOC emissions in areas more distant than Europe.