A five year record of high-frequency in situ measurements of non-methane hydrocarbons at Mace Head, Ireland

摘要

Continuous high-frequency in situ measurements of a range of non-methanehydrocarbons have been made at Mace Head since January 2005. Mace Head is abackground Northern Hemispheric site situated on the eastern edge of theAtlantic. Five year measurements (2005–2009) of six C₂–C₅non-methane hydrocarbons have been separated into baseline NorthernHemispheric and European polluted air masses, among other sectors. Seasonalcycles in baseline Northern Hemispheric air masses and European polluted airmasses arriving at Mace Head have been studied. Baseline air masses show abroad summer minima between June and September for shorter lived species,longer lived species show summer minima in July/August. All speciesdisplayed a winter maxima in February. European air masses showed baselineelevated mole fractions for all non-methane hydrocarbons. Largest elevations(of up to 360 ppt for ethane maxima) from baseline data were observed inwinter maxima, with smaller elevations observed during the summer. Analysisof temporal trends using the Mann-Kendall test showed small (<6 % yr−1)but statistically significant decreases in the butanes and i-pentane between2005 and 2009 in European air. No significant trends were found for anyspecies in baseline air.