The influence of weather-type and long-range transport on airborne particle concentrations in Edinburgh, UK

This study investigated the influence of regional-scale synoptic weather type and geographical source regions of air masses on two-particle concentration metrics (Black Smoke (BS) and PM10) in the city of Edinburgh, UK, between 1981 and 1996. Twenty-seven classifications of Jenkinson Daily Weather Types (JWT) were sub-divided into 9 directional categories and 3 vorticity categories, and the influence of JWT category on BS and PM10 determined. Four-day air mass back-trajectories for 1 July 1995–30 June 1996 were computed and grouped into 8 categories depending on the geographical route followed. Significantly elevated concentrations of BS (median values 2, 5 and 4 μg m−3 greater than median for 1981–1996) and PM10 (median values 3, 5.5 and 8 μg m−3 greater than median for 1992–1996) were observed for anticyclonic, southerly and south-easterly weather types, respectively. These differences were not identified at conventional levels of significance for BS in 1995–1996. This may reflect a shift in more recent times to lower concentrations of predominantly locally emitted BS less affected by regional scale meteorology. Conversely, significant inter-trajectory category differences were observed for PM10 during 1995–1996, with highest concentrations associated with Eastern European trajectories and south-easterly weather type categories (11.4 and 10.7 μg m−3 greater than annual means, respectively). The variation in particle concentration across weather-type was a significant proportion of total median particle concentration, and of a magnitude associated with adverse health outcomes. Thus current PM10 concentrations (and associated health outcomes) in Edinburgh are likely to be significantly influenced by regional-scale meteorology independent of local air quality management areas. Furthermore, changes in long-term trends in distributions of synoptic weather types indicate that future climate change may influence exposure to PM10 and the PM10:BS ratio in Edinburgh. Further definition of the relationships between long-range transport and particle concentration will improve classification of human exposure in epidemiological studies.