Abstract

Abstract. The atmospheric concentration of elemental carbon (EC) in Europe during the six-year period 2005–2010 has been simulated with the EMEP MSC-W model. The model bias compared to EC measurements was less than 20% for most of the examined sites. The model results suggest that fossil fuel combustion is the dominant source of EC in most of Europe but that there are important contributions also from residential wood burning during the cold seasons and, during certain episodes, also from open biomass burning (wildfires and agricultural fires). The modelled contributions from open biomass fires to ground level concentrations of EC were small at the sites included in the present study, <3% of the long-term average of EC in PM10. The modelling of this EC source is subject to many uncertainties, and it was likely underestimated for some episodes. EC measurements and modelled EC were also compared to optical measurements of black carbon (BC). The relationships between EC and BC (as given by mass absorption cross section, MAC, values) differed widely between the sites, and the correlation between observed EC and BC is sometimes poor, making it difficult to compare results using the two techniques and limiting the comparability of BC measurements to model EC results. A new bottom-up emission inventory for carbonaceous aerosol from residential wood combustion has been applied. For some countries the new inventory has substantially different EC emissions compared to earlier estimates. For northern Europe the most significant changes are much lower emissions in Norway and higher emissions in neighbouring Sweden and Finland. For Norway and Sweden, comparisons to source-apportionment data from winter campaigns indicate that the new inventory may improve model-calculated EC from wood burning. Finally, three different model setups were tested with variable atmospheric lifetimes of EC in order to evaluate the model sensitivity to the assumptions regarding hygroscopicity and atmospheric ageing of EC. The standard ageing scheme leads to a rapid transformation of the emitted hydrophobic EC to hygroscopic particles, and generates similar results when assuming that all EC is aged at the point of emission. Assuming hydrophobic emissions and no ageing leads to higher EC concentrations. For the more remote sites, the observed EC concentration was in between the modelled EC using standard ageing and the scenario treating EC as hydrophobic. This could indicate too-rapid EC ageing in the model in relatively clean parts of the atmosphere.

Highlights

  • Black carbon (BC) particles, a major component of soot, may heat the atmosphere and have a warming effect on the climate

  • We found large differences between elemental carbon (EC) and BC for most of the stations investigated in this study (Fig. 2)

  • All BC data were normalized with EC data from the same station to produce EC-equivalent BC values, BCe, using site-specific mass absorption cross section (MACe) values

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Summary

Introduction

Black carbon (BC) particles, a major component of soot, may heat the atmosphere and have a warming effect on the climate. Janssen et al (2011) have recently reviewed epidemiological studies of evaluated adverse health effects of PM mass and black carbon particles, BCP (here BCP includes BC, elemental carbon (EC) and black smoke). The estimated health effects per μg m−3 were found to be substantially higher for BCP than for PM10 or PM2.5. Another recent review of health effects of PM and its components (Rohr and Wyzga, 2012) pointed out the importance of carbon-containing PM components, i.e. both EC and OC (organic carbon)

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