Organic and black carbon in PM2.5 and PM10:: 1 year of data from an urban site in Helsinki, Finland

The results from a 1-year measurement period concerning the diurnal PM2.5 and PM10 organic carbon (OC) and black carbon (BC) concentrations are presented for a traffic-influenced site in the Helsinki metropolitan area. The measurements were based on aerosol sampling using a virtual impactor and the subsequent thermal-optical analysis to distinguish between OC and BC. Backup filters were used to estimate and correct for the positive sampling artefact. Daily-average concentrations in PM2.5 varied between 1.0 and 8.5 mug C m(-3) for OC, and between 0.3 and 5.7 mug C m(-3) for BC. Annual-average concentrations of OC and BC were 3.0 and 1.2 mug C m(-3), respectively, in PM2.5, and 4.2 and 1.3 mug C m(-3) in PM10. On an annual level, particulate organic matter (POM = 1.6 x OC) accounted for 50 +/- 14% and 36 +/- 8% (average+/- 1sigma) of the total PM2.5 and PM10, respectively, whereas BC stayed lower at 14+/-8% and 7+/-4%. Typically more than 90% of BC resided in the PM2.5 size fraction. The contribution of coarse particles (> 2.5 mum) to the overall OC varied between the 0% and 67% (median 27%). The effect of meteorological conditions on the variability of OC and BC concentrations was examined, and the contribution of secondary organic aerosol to the total fine organic aerosol was estimated. (C) 2002 Elsevier Science Ltd. All rights reserved.