The contributions to long-term health-relevant particulate matter at the UK EMEP supersites between 2010 and 2013: Quantifying the mitigation challenge

At Harwell the mean (± 1 sd) 2010-2013 annual average concentrations were PM10 = 16.4 ± 1.4 μg m− 3 and PM2.5 = 11.9 ± 1.1 μg m− 3 and at Auchencorth PM10 = 7.4 ± 0.4 μg m− 3 and PM2.5 = 4.1 ± 0.2 μg m− 3. The chemical climate state at each site showed that frequent, moderate hourly PM10 and PM2.5 concentrations (defined as approximately 5-15 μg m− 3 for PM10 and PM2.5 at Harwell and 5-10 μg m− 3 for PM10 at Auchencorth) determined the magnitude of annual average PM10 and PM2.5 to a greater extent than the relatively infrequent high, episodic PM10 and PM2.5 concentrations. These moderate PM10 and PM2.5 concentrations were derived across the range of chemical components, seasons and air-mass pathways, in contrast to the highest PM concentrations which tended to associate with specific conditions. For example, the largest contribution to moderate PM10 and PM2.5 concentrations - the secondary inorganic aerosol components, specifically NO3− - were accumulated during the arrival of trajectories traversing the spectrum of marine, UK, and continental Europe areas. Mitigation of the long-term health-relevant PM impact in the regions characterised by these two sites requires multilateral action, across species (and hence source sectors), both nationally and internationally; there is no dominant determinant of the long-term PM metrics to target.