Abstract
Abstract. Measurements of equivalent black carbon (EBC) in aerosols at the high Arctic field site Villum Research Station (VRS) at Station Nord in North Greenland showed a seasonal variation in EBC concentrations with a maximum in winter and spring at ground level. Average measured concentrations were about 0.067 ± 0.071 for the winter and 0.011 ± 0.009 for the summer period. These data were obtained using a multi-angle absorption photometer (MAAP). A similar seasonal pattern was found for sulfate concentrations with a maximum level during winter and spring analyzed by ion chromatography. Here, measured average concentrations were about 0.485 ± 0.397 for the winter and 0.112 ± 0.072 for the summer period. A correlation between EBC and sulfate concentrations was observed over the years 2011 to 2013 stating a correlation coefficient of R2 = 0.72. This finding gives the hint that most likely transport of primary emitted BC particles to the Arctic was accompanied by aging of the aerosols through condensational processes. BC and sulfate are known to have only partly similar sources with respect to their transport pathways when reaching the high Arctic. Aging processes may have led to the formation of secondary inorganic matter and further transport of BC particles as cloud processing and further washout of particles is less likely based on the typically observed transport patterns of air masses arriving at VRS. Additionally, concentrations of EC (elemental carbon) based on a thermo-optical method were determined and compared to EBC measurements. EBC measurements were generally higher, but a correlation between EC and EBC resulted in a correlation coefficient of R2 = 0.64. Model estimates of the climate forcing due to BC in the Arctic are based on contributions of long-range transported BC during spring and summer. The measured concentrations were here compared with model results obtained by the Danish Eulerian Hemispheric Model, DEHM. Good agreement between measured and modeled concentrations of both EBC/BC and sulfate was observed. Also, the correlation between BC and sulfate concentrations was confirmed based on the model results observed over the years 2011 to 2013 stating a correlation coefficient of R2 = 0.74. The dominant source is found to be combustion of fossil fuel with biomass burning as a minor, albeit significant source.
Highlights
Black carbon (BC) is a component of the atmospheric aerosol, which originates from incomplete combustion of fossil fuels or waste, flaring or natural and anthropogenic biomass burning (Roberts and Jones, 2004; Stohl et al, 2013; Yttri et al, 2014)
Differences between the two parameters are expected since the equivalent black carbon (EBC) and elemental carbon (EC) concentrations are based on two different measurement techniques which both experience several problems due to different artifacts
The examined equivalent black carbon/black carbon (EBC/BC) and sulfate concentrations exhibit very similar patterns characterized by higher concentrations in winter/spring compared to summer, which is in accordance with the seasonal cycle of Arctic Haze observed in Arctic regions by several authors (Heidam et al, 1984, 1999, 2004; Iversen et al, 1984; Barrie et al, 1989; Stohl et al, 2007)
Summary
Black carbon (BC) is a component of the atmospheric aerosol, which originates from incomplete combustion of fossil fuels or waste, flaring or natural and anthropogenic biomass burning (Roberts and Jones, 2004; Stohl et al, 2013; Yttri et al, 2014). In case of haze situations the energy can be re-emitted via long-wave radiation (Lubin and Simpson, 1994) This results in a heating effect below and within the polluted aerosol layer (e.g. AMAP report, 2011). After a certain degree of chemical aging BC particles may have taken up inorganic matter and such coating can lead to modified particles with sufficient CCN activity In this way, aged BC particles may affect the radiation budget indirectly by acting as CCN or ice nuclei (IN) and thereby they may change cloud albedo (Koehler et al, 2009). Sulfate particles are very efficient in scattering incoming solar radiation resulting in a cooling effect (Crutzen, 2006) These particles are highly associated with aging processes as they appear as secondary inorganic aerosols, e.g. as (NH4)2SO4 or NH4HSO4 (Seinfeld and Pandis, 2006). It has to be clarified that measurements reported in this study were made near the surface and that radiative forcing depends on the entire column burden
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