Elsevier

Atmospheric Environment

Volume 45, Issue 24, August 2011, Pages 4042-4050
Atmospheric Environment

Aerosol black carbon at five background measurement sites over Finland, a gateway to the Arctic

https://doi.org/10.1016/j.atmosenv.2011.04.026Get rights and content

Abstract

Aerosol equivalent black carbon (BCe) was measured at five different background stations in Finland, with the longest data set from Hyytiälä, December 2004–December 2008. Measurements were conducted either with an aethalometer or a Multi-Angle Absorption Photometer, MAAP. Measured black carbon concentrations were highest in Virolahti in southeastern Finland, with annual averages ranging from 385 to 460 ng m−3, followed by Hyytiälä (250–370 ng m−3), Utö (230–270 ng m−3), Puijo (225–230 ng m−3), and Pallastunturi (60–70 ng m−3) in northern Finland. The BCe fractions of measured PM2.5 concentrations were generally between 5 and 10%, with highest fractions at Virolahti close to the Eastern border. At all the stations, the highest concentrations were observed during the spring and the winter, and the lowest concentrations during the summer. The seasonal cycle could generally be attributed to the reaching of long-range-transported black carbon. Additional reasons were increasing domestic wood burning and reduced boundary-layer height during winter, and a more effective vertical mixing during summer. The highest concentrations for each station occurred with southerly winds, and on the basis of trajectory analyses, the source areas of BCe resided mostly in Central and Eastern Europe. Occasionally the long-range-transported BCe concentrations were elevated for short periods to fulfill the characteristics of pollution episodes. From these episodes, about 62% were a result of non-fire anthropogenic sources and 36% due to open biomass burning sources. Episodes from the biomass burning sources were most often observed during the spring.

Highlights

► Long term black carbon measurements reported in and close to the Arctic. ► Trans-boundary transport a major source of black carbon in clean areas. ► Open biomass burning a reason for transported black carbon in Northern Europe.

Introduction

Black carbon (BC), a byproduct of fossil fuel combustion and biomass burning, is an important component of atmospheric particulate matter (Bond et al., 2004). Being a strong absorber of solar radiation, BC may have significant regional effects on temperature, cloud amount and precipitation (Menon et al., 2002, Ramanathan and Carmichael, 2008, Johnson, 2009, Jacobson, 2010, Koch and Del Genio, 2010). Over snow-covered areas, the surface albedo can be significantly reduced due to the deposition of BC onto snow (e.g. Warren and Wiscombe, 1980). This may significantly influence the local and regional climate (Flanner et al., 2009). Direct observations of reduced albedo resulting from long-range-transported BC into Arctic areas were reported by Stohl et al. (2006). More recently, it was estimated that BC may have contributed to more than half of the observed Arctic warming since 1890, most of this occurring during the last three decades (Shindell and Faluvegi, 2009).

There are large uncertainties associated with emissions of BC to the atmosphere, its aging during atmospheric transportation, and its removal by precipitation (Bond et al., 2004, Riemer et al., 2004, Hoelzemann et al., 2004, Generoso et al., 2003, Khalizov et al., 2009). All these uncertainties propagate directly into global model simulations (Stier et al., 2007, Koch et al., 2010, Bauer et al., 2010, Vignati et al., 2010). For a better understanding of the transportation, removal and climatic impacts of atmospheric BC, accurate and up-to-date knowledge of its global distribution is clearly needed. Concerning remote, northern parts of Europe, little information on the concentration levels and temporal variability of BC is available (Ricard et al., 2002, Eleftherias et al., 2009, Yttri et al., 2007, Hirdman et al., 2010). Such data would be of great value when studying the effects of BC on Arctic climate and when evaluating atmospheric models that simulate the long range atmospheric transport of BC.

This paper provides an overview on the temporal and spatial variability of BC in atmospheric aerosols over Finland in Northern Europe. The analysis is based on measurements made at five Finnish background stations until the end of 2008. The longest data set is from Hyytiälä, beginning December 2004. In addition to looking at BC concentration levels and their seasonal variability, we investigate the connection of BC with typical meteorological quantities and assess the major source types and -areas for BC observed in Finland. Pollution episodes of BC at the different stations are also examined.

Section snippets

Measurement sites

The measurement stations have been described in recent literature and only a short overview is given here. The measurements were conducted at five different locations in Finland (Fig. 1).

The GAW (Global Atmosphere Watch) station at Pallastunturi (e.g. Hatakka et al., 2003) is in the subarctic region at the limit of the northern boreal forest zone. Having multiple sub-stations, the measurements were conducted at the main station on Sammaltunturi, 565 m a.s.l. There are no significant local or

BCe at individual sites

First, we analyzed the results from each station individually. This was done in light possible correlations of BCe on wind direction (Fig. 2) and diurnal variations (Supplementary material). The possible local and regional sources and locations of major cities were checked. As expected, emissions from the Kuopio city were observed in the BCe data from Puijo. This was mostly seen as concentration peaks during morning and evening. The peaks were related to work-related traffic and utilization of

Conclusions

Aerosol black carbon was measured at five different background stations in Finland with the longest data set from Hyytiälä covering a period from 8 December 2004 to 31 December 2008. BCe concentrations measured in Southern Finland, Virolahti were the highest, and in Northern Finland, Pallastunturi the lowest. At all the stations, highest concentrations were observed during the spring and the winter, and the lowest ones during the summer.

None of the major Finnish cities seemed to have a

Acknowledgments

FLEXPART calculations were made as part of the project EUCAARI, which is funded by the European Commission. Academy of Finland and Maj & Tor Nessling foundation are acknowledged for funding. Partial funding for FLEXPART was provided through NFR grant #ES432275.

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