Variations and sources of the equivalent black carbon in the high Arctic revealed by long‐term observations at Alert and Barrow: 1989–2003

Abstract

[1] Fifteen years of ''equivalent'' black carbon (EBC) measurements (derived from aethalometer measurements of light absorption) made at Alert in Nunavut, Canada, and Point Barrow in Alaska, United States, were compared for the long-term trends and seasonal cycle. Over the 15-year period from 1989 to 2003, the results revealed a downward trend in EBC concentrations by as much as 54% at Alert and 27% at Barrow for the all-year data, by 49% at Alert and 33% at Barrow for the winter data, and by 53% at Alert for the summer. It was difficult to quantify if there was a decline during the summer for Barrow since there was no clear trend. The difference in trends might be related to changes in circulation in the Arctic, variable source contribution, and/or scavenging of particles. The results revealed that EBC concentrations were 40% higher during the positive phase of the North Atlantic Oscillation than during the negative phase. The source contributions at the two sites were determined by using trajectory analysis techniques, which revealed that Alert came under the influence of Siberia/Europe transport while Barrow showed influence from Siberian and Pacific/Asian transport.

Long‐term trend analysis of aerosol variables at the high‐alpine site Jungfraujoch

“…The clear decrease of the scattering coefficient at Point Barrow (8 m asl) for the time period 1976 to 1984 was attributed to a decrease of anthropogenic emissions from Europe and Russia [Bodhaine, 1989]. A decrease of the absorption coefficient determined with an aethalometer was found for the high Arctic also the period 1989 -2000, which then was followed by an increase [Sharma et al, 2006]. However, the different elevation of the previous measurement sites compared with the sites in the high Arctic and the difference in time period prevents any reasonable comparison.…”

An update on polar aerosol optical properties using POLAR-AOD and other measurements performed during the International Polar Year

“…For favourable dynamical conditions, long-lived aerosol of natural and anthropogenic origin can be transported episodically from mid-to high-latitudes during the winter months, and then trapped within the Arctic vortex. These particles accumulate and grow during their life, being subject to variations in chemical composition similar to those measured by Quinn et al (2007) and Sharma et al (2002Sharma et al ( , 2006. The analysis of the monthly mean values of AOD obtained from the data collected during AH episodes indicates that both magnitude of AOD and frequency of AH episodes have been subject to large fluctuations from one season to another, without presenting a stable long-term variation in AOD.…”

“…The exception was the winterespring data found by Ström et al (2003) at the Zeppelin station (474 m a.m.s.l.) above NyÅlesund, which gave considerably lower values of u o probably owing to a higher content of combustion particles measured at the Svalbard site than those sampled at Barrow by Sharma et al (2002Sharma et al ( , 2006. Tomasi et al (2007), omitting the data measured during the 1982e1984 and the 1991e1994 periods, which were strongly affected by the El Chichón and the Pinatubo (and Cerro Hudson) volcanic eruptions (Herber et al, 1993(Herber et al, , 1996.…”

“…These estimates were given by Quinn et al (2007) in terms of monthly mean concentrations of aerosol mass constituents, such as sea salt, non-sea salt (nss) sulphate, methane sulphonic acid (MSA), ammonium ions, and nss K, Mg and Ca ions, for both the submicron and supermicron size ranges. In the present study, the above data were integrated by (i) the estimates of total carbon (black carbon (BC) þ organic carbon (OC)) concentration measured by Sharma et al (2002Sharma et al ( , 2006 at Barrow, and (ii) the conversion from the above nss Mg and Ca ionic concentrations to the AleSi components, using the soil factors proposed by Polissar et al (1998) for the Northwest Alaska areas. For such features of particulate matter composition, the percentage mass fractions were determined for sulphates, nitrates, sea salt, mineral dust, water-soluble organic matter (WSOM) and BC components, in the submicron, supermicron and overall size-distributions, during the summer period from June to September, and for the rest of the year.…”

Sensitivity of remote aerosol distributions to representation of cloud–aerosol interactions in a global climate model

“…The observed distinct seasonal cycle with a minimum in summer and a maximum in late winter and early spring (Sharma et al, 2006) is closely related to transport from source regions outside the Arctic. Aerosol dry/wet removal at lower latitudes can strongly influence the distribution of aerosols at high latitudes (e.g., Kinne et al, 2006;Textor et al, 2007;Shindell et al, 2008;Bourgeois and Bey, 2011;Browse et al, 2012).…”