Concentrations and Estimated Soot Content of PM1, PM2.5, and PM10in a Subarctic Urban Atmosphere

Mass concentrations of ambient particulate matter were measured in terms of daily average values of PM 1, PM 2.5, and PM 10 for 6 months during the winter of 1996−1997 at a fixed sampling site in Helsinki, Finland, along with meteorological parameters and particle number concentra tions in the size range 0.01−1 μm. 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 and spring) in order to study more closely seasonal phenomena that have an effect on air pollution patterns. The variations in PM 10 and PM 2.5 concentrations differed in pattern during resuspended dust episodes, whereas those in PM 1 concentrations followed those in PM 2.5 fairly well throughout the 6-month measurement period. Thus it seems that PM 1 does not provide much additional information on mass concentrations relative to PM 2.5 . Number concentrations in the ultrafine particle size range from 0.01 to 0.1 μm, especially in wintertime, were much better correlated with absorption coefficients than with any of the three PM mass-based concentrations, indicating that Black Smoke particles are related to that size range. The results also indicate that coarse particle concentrations in ambient air are affected more by seasonal factors than are fine particle concentrations.