Volatile organic compounds in the western Mediterranean basin: urban and rural winter measurements during the DAURE campaign

摘要

Atmospheric volatile organic compounds (VOCs) have key environmental andbiological roles, but little is known about the daily VOC mixing ratios inMediterranean urban and natural environments. We measured VOC mixing ratiosconcurrently at an urban and a rural site during the winter DAURE campaignin the northeastern Iberian Peninsula, by means of PTR-MS at both locations:a PTR-Quad-MS at the urban site and a PTR-ToF-MS at the rural site. All VOCmixing ratios measured were higher at the urban site (e.g. acetaldehyde,isoprene, benzene, and toluene with averages up to 1.68, 0.31, 0.58 and 2.71 ppbv, respectively), with the exception of some short-chain oxygenated VOCssuch as acetone (with similar averages of 0.7–1.6 ppbv at both sites). Theaverage diurnal pattern also differed between the sites. Most of the VOCs atthe urban location showed their highest mixing ratios in the morning andevening. These peaks coincided with traffic during rush hour, the mainorigin of most of the VOCs analyzed. Between these two peaks, the sea breezetransported the urban air inland, thus helping to lower the VOC loading atthe urban site. At the rural site, most of the measured VOCs were advectedby the midday sea breeze, yielding the highest daily VOC mixing ratios (e.g.acetaldehyde, isoprene, benzene, and toluene with averages up to 0.65, 0.07,0.19, and 0.41 ppbv, respectively). Only biogenic monoterpenes showed aclear local origin at this site. In addition, the concentrations of fineparticulate matter observed at both sites, together with the synopticmeteorological conditions and radio-sounding data, allowed theidentification of different atmospheric scenarios that had a clear influenceon the measured VOC mixing ratios. These results highlight the differencesand relationships in VOC mixing ratios between nearby urban and rural areasin Mediterranean regions. Further research in other urban-rural areas iswarranted to better understand the urban-rural influence on atmospheric VOCmixing ratios under different atmospheric conditions.