Abstract
Abstract. We deployed an aerosol mass spectrometer during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) summer campaign in Greenland in June/July 2008 on the research aircraft ATR-42. Online size resolved chemical composition data of submicron aerosol were collected up to 7.6 km altitude in the region 60 to 71° N and 40 to 60° W. Biomass burning (BB) and fossil fuel combustion (FF) plumes originating from North America, Asia, Siberia and Europe were sampled. Transport pathways of detected plumes included advection below 700 hPa, air mass uplifting in warm conveyor belts, and high altitude transport in the upper troposphere. By means of the Lagrangian particle dispersion model FLEXPART, trace gas analysis of O3 and CO, particle size distributions and aerosol chemical composition 48 pollution events were identified and classified into five chemically distinct categories. Aerosol from North American BB consisted of 22% particulate sulphate, while with increasing anthropogenic and Asian influence aerosol in Asian FF dominated plumes was composed of up to 37% sulphate category mean value. Overall, it was found that the organic matter fraction was larger (85%) in pollution plumes than for background conditions (71%). Despite different source regions and emission types the particle oxygen to carbon ratio of all plume classes was around 1 indicating low-volatility highly oxygenated aerosol. The volume size distribution of out-of-plume aerosol showed markedly smaller modes than all other distributions with two Aitken mode diameters of 24 and 43 nm and a geometric standard deviation σg of 1.12 and 1.22, respectively, while another very broad mode was found at 490 nm (σg = 2.35). Nearly pure BB particles from North America exhibited an Aitken mode at 66 nm (σg = 1.46) and an accumulation mode diameter of 392 nm (σg = 1.76). An aerosol lifetime, including all processes from emission to detection, in the range between 7 and 11 days was derived for North American emissions.
Highlights
After the discovery of haze layers in late winter and early spring in the lower Arctic atmosphere by pilots overflying Canada and Alaska in the 1950s (Greenaway, 1950; Mitchell, 1956) numerous campaigns and continuous measurements of Arctic aerosol have been conducted (Rahn et al, 1977; Schnell, 1984; Shaw, 1995; Law and Stohl, 2007; Quinn et al, 2007, and references therein)
In this paper we present the chemical composition and origin of submicron aerosol in the free troposphere over Greenland measured by an aircraft-based Aerodyne aerosol mass spectrometer (AMS) during the POLARCAT-France experiment in June/July 2008
European sources were mostly of anthropogenic nature, while a second biomass burning (BB) influence originated from the Yakutsk area (Paris et al, 2009) in Siberia usually mixed with anthropogenic emissions from East Asia
Summary
After the discovery of haze layers in late winter and early spring in the lower Arctic atmosphere by pilots overflying Canada and Alaska in the 1950s (Greenaway, 1950; Mitchell, 1956) numerous campaigns and continuous measurements of Arctic aerosol have been conducted (Rahn et al, 1977; Schnell, 1984; Shaw, 1995; Law and Stohl, 2007; Quinn et al, 2007, and references therein). Due to the sulphur content in fossil fuels, FF is associated with the formation of particulate sulphate from SO2 emissions, while biomass burning emissions have a low sulphur content (Andreae and Merlet, 2001) Both sources emit gasphase and particulate organic compounds which contribute to carbonaceous particulate matter in the pollution plumes either directly or by gases partitioning into the particle phase (Donahue et al, 2009). Because of the long transport times of up to more than two weeks the aerosol arriving over Greenland is expected to be highly oxygenated due to chemical ageing (Jimenez et al, 2009) as confirmed by surface measurements of PM2.5 chemical composition at Summit, central Greenland (von Schneidemesser et al 2009; Hagler et al 2007) Properties such as optical behaviour, hydrophobicity/hygroscopicity and size distributions are expected to be different from near source aerosol. Long-range transport air masses, the identification of emission source regions and their associated aerosol chemical characteristics, as well as particle lifetimes and size distributions
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