Daily, weekly and seasonal relationships among VOCs, NOx x and O3 in a semi-urban area near Barcelona

Daily, weekly, and seasonal patterns of O₃, NOx _x and VOCs and their relationship to meteorological conditions were studied in a semi-urban site near Barcelona by means of five-day long campaigns that included weekend and labor days in December, March, June, and October. The plant protection thresholds for ozone and NO₂ were exceeded, respectively, on all the studied days in summer and on all the studied days. Ozone formation was predominantly local and relied on photochemical processes with VOCs playing a controlling role. Formaldehyde, acetaldehyde, methanol, toluene, isoprene, and acetone (in this order) presented the highest O₃ formation potential during the studied periods. These results highlight the important role in O₃ formation played by VOC species such as acetaldehyde, methanol, and acetone, that all have a significant biogenic component. Thus, these VOCs must be taken into account in the discussion of any ozone abatement strategy.