Local and regional sources of C(2)-C (8) hydrocarbon concentrations at a sub-urban motorway site (M4) in Ireland.

Approximately 8 months of C(2)-C(8) online-sampling of hydrocarbons was carried out in the vicinity of a sub-urban Motorway in Ireland. A comprehensive description of air quality monitoring adjacent to the M4 at Leixlip in Ireland is presented where the primary objective was to ascertain the local and regional C(2)-C(8) hydrocarbon emissions in the vicinity of a sub-urban Motorway (M4). Nineteen HC compounds were monitored where different analysis techniques were employed in an attempt to isolate the Motorway source effect. Included in these were analyses into various hydrocarbon ratios, including 1,3 butadiene/propene, m + p xylene/ethylbenzene and ethene/acetylene. In addition, the local source effect was quantitatively assessed using COPERTIII and CALINE4 modelling, and the regional effects and source contributions were analysed using 2-D back trajectory analysis. Our results show that conditions associated with high regional contributions are associated with conditions also conducive to high local contributions, particularly evident at the M4 site due to the road orientation, as air masses from continental Europe and the UK are likely to be associated with near parallel, slow moving local winds relative to the M4, yielding higher local contributions.