Abstract
An air mass type approach was employed to investigate the dependence of winter and summer pollutant concentrations at two sites in central Glasgow on weather conditions over the period from 2005 to 2020. A two-stage synoptic typing process of principal component analysis (PCA) and cluster analysis was used to establish the air mass types. Daily means of seven surface meteorological variables calculated from hourly observations were entered into P-mode PCA. Three (two) principal components explained 72.2% (60.2%) of the variance in winter (summer). Days with similar weather conditions were grouped together to produce six clusters (air mass types) for both winter and summer. There were statistically significant ( p < 0.05) differences in daily mean O 3 , PM 10 , NO x , NO 2 and CO between the six air mass types in both seasons. Apart from PM 10 , variations in pollutant concentration with air mass type were more pronounced in winter than in summer. In winter, the highest mean NO x , NO 2 and PM 10 concentrations occurred under the continental air mass, which is usually associated with high pressure, calm conditions limiting dispersion and the transport of pollutants from Continental Europe on a southeasterly wind. Furthermore, most breaches of air quality guidelines for NO 2 and PM 10 occurred in winter occurred under that air mass type. However, it is not possible to determine from these results whether local meteorological conditions or long-range transport is the most important cause of poor air quality under the continental air mass type. Pollutant concentrations are generally lower in summer (apart from O 3 ). Poor summer air quality was found to occur disproportionately under stable anticyclonic tropical and tropical continental air mass types.