Major component contributions to PM10 composition in the UK atmosphere

Physical and chemical characteristics of PM10, including chloride, nitrate, sulphate, and black smoke, have been measured on a seasonal basis at four coastal, rural, and urban sites across the UK. Weekly campaigns with 6 h sample resolution were conducted, and the results related to meteorological conditions and air mass back trajectories. Seasonal and location- specific mean values are reported, along with an indication of diurnal characteristics. Although the urban site reflected generally higher values for the anthropogenic pollutants, long-range transport of primary and secondary particles was significant. The data have been analysed using a four-component multi-linear regression model including black smoke as a surrogate for primary combustion particles, secondary particles (sulphate and nitrate), chloride, and a constant which describes “other”, mainly coarse mode particles. Regression coefficients have been calculated on a site and seasonal basis. “Other” particles were higher during the summer and in the urban environment with an overall mean value of 5 μg m−3. Secondary nitrate and sulphate were strongly related to meteorological conditions and less to location. Overall, the four-component model accounts quite well (r2=0.76 for all data) for PM10 mass and for some sites and seasons gives an excellent fit to the data. Addition of dummy variables representing season, urban/rural location and time of sampling gives an improvement in fit, with r2=0.84. Application of the coefficients derived from the “all data” model shows secondary particles contributing 28–35% of site-mean PM10, primary combustion particles from 20 to 57%, sodium chloride, 11–34% and “other”, mainly crustal particles, 3–21%. It is felt that this probably underestimates the crustal contribution, but the reasons are unclear.