Concentrations and estimated soot content of PM1, PM2.5, and PM10 in a subarctic urban atmosphere

Mass concentrations of ambient particulate matter were measured in terms of daily average values of PM1, PM2.5, and PM10 for 6 months during the winte r of 1996-1997 at a fixed sampling site in Helsinki, Finland, along with me teorological parameters and particle number concentrations in the size rang e 0.01-1 mu m. In addition, the PM filters were subjected to reflectometric analysis to determine absorption coefficients for the various fractions of urban particulate matter. The data were divided into two periods (winter a nd spring) in order to study more closely seasonal phenomena that have an e ffect on air pollution patterns. The variations in PM10 and PM2.5 concentra tions differed in pattern during resuspended dust episodes, whereas those i n PM1 concentrations followed those in PM2.5 fairly well throughout the 6-m onth measurement period. Thus it seems that PM1 does not provide much addit ional information on mass concentrations relative to PM2.5 Number concentra tions in the ultrafine particle size range from 0.01 to 0.1 mu m, especiall y in wintertime, were much better correlated with absorption coefficients t han with any of the three PM mass-based concentrations, indicating that Bla ck Smoke particles are related to that size range. The results also indicat e that coarse particle concentrations in ambient air are affected more by s easonal factors than are fine particle concentrations.