Concentrations of ultrafine, fine and PM2.5 particles in three European cities

Total number concentrations, number concentrations of ultrafine (0.01-0.1 m um) and accumulation (0.1-0.5 mum) particles, as well as mass concentration of PM2.5 particles and blackness of PM2.5 filters, which is related to Bla ck Smoke were simultaneously monitored in three European cities during the winter period for three and a half months. The purpose of the study was to describe the differences in concentration levels and daily and diurnal vari ations in particle number and mass concentrations between European cities. The results show statistically significant differences in the concentration s of PM2.5 and the blackness of the PM2.5 filters between the cities, but n ot in the concentrations of ultrafine particles. Daily PM2.5 levels were fo und to be poorly correlated with the daily total and ultrafine number conce ntrations but better correlated with the number concentration of accumulati on particles. According to the principal component analysis airborne partic ulate pollutants seem to be divided into two major source categories, one i dentified with particle number concentrations and the other related to mass -based information. The present results underline the importance of using b oth particle number and mass concentrations to evaluate urban air quality. (C) 2001 Elsevier Science Ltd. All rights reserved.