Source attribution of Arctic black carbon constrained by aircraft and surface measurements

Abstract

Abstract. Black carbon (BC) contributes to Arctic warming, yet sources of Arctic BC and their geographic contributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Barrow and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measurements at Alert. The springtime airborne measurements performed by the NETCARE campaign in 2015 and the PAMARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and include profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domestic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE = 17 %) except for an underestimation in the middle troposphere (500-700 hPa).Sensitivity simulations suggest that anthropogenic emissions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annually (37 %), with the largest contribution in the middle troposphere (400-700 hPa). Anthropogenic emissions from northern Asia contribute considerable BC (27 % in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually.At the Arctic surface, anthropogenic emissions from northern Asia (40-45 %) and eastern and southern Asia (20-40 %) are the largest BC contributors in winter and spring, followed by Europe (16-36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow.Our adjoint simulations indicate pronounced spatial heterogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oilfields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

Temporally delineated sources of major chemical species in high Arctic snow

“…The relative importance of fossil fuel combustion and biomass burning differs between studies, likely indicating a strong dependence on location (especially high vs. low Arctic), season, or differences in source breakdown year to year (e.g., McConnell et al, 2007;Doherty et al, 2010;Dou et al, 2012;Law et al, 2014). A recent study by Xu et al (2017) analyzing airborne measurement from a similar time period as this study found about 90 % of BC to likely be anthropogenic in source, primarily from Eurasia, supporting the assessment above. Several modelling studies have suggested that combined anthropogenic sources account for 65-96 % m/m of BC in Arctic snow, especially elevated over the winter months with spring and summer proportions dependent on the frequency of forest fires of that year (Flanner et al., 2007;Skeie et al, 2011;Wang et al, 2011;Sharma et al, 2013;Breider et al, 2014;Xu et al, 2017).…”

“…A recent study by Xu et al (2017) analyzing airborne measurement from a similar time period as this study found about 90 % of BC to likely be anthropogenic in source, primarily from Eurasia, supporting the assessment above. Several modelling studies have suggested that combined anthropogenic sources account for 65-96 % m/m of BC in Arctic snow, especially elevated over the winter months with spring and summer proportions dependent on the frequency of forest fires of that year (Flanner et al., 2007;Skeie et al, 2011;Wang et al, 2011;Sharma et al, 2013;Breider et al, 2014;Xu et al, 2017). In particular, modelling studies have shown winter Arctic BC to be dominated by flaring and other mixed industry emissions, with less impact from anthropogenic biomass burning Stohl et al, 2013).…”

“…These source regions correspond with known flaring and industrial BC sources (in the vicinity of the Ob and Pechora rivers and the Taymyrsky DolganoNenetsky District, respectively) (Huang et al, 2015;Winiger et al, 2017). A winter central Eurasian source of BC was also identified by Xu et al (2017), specifically flaring in western Siberia. However, this central Asian source was found to be a smaller contributor of total Arctic BC than eastern Asia.…”

Organic functional groups in the submicron aerosol at 82.5° N, 62.5° W from 2012 to 2014

“…6). Region 1 includes emissions from gas flaring that are believed to be a significant source of BC to the high Arctic (e.g., Stohl et al, 2013;Sand et al, 2013;Qi et al, 2017;Xu et al, 2017). Figure 7b shows the monthly-averaged time series of the same two quantities shown in Fig.…”

“…Simulations by Fisher et al (2011) suggest sources of sulfate at the world's northernmost continuous aerosol observatory situated on the shore of the Arctic Ocean (Alert, Nunavut, Canada) are dominated by west Asia/Siberia, Europe, oxidation of dimethyl sulfide (DMS) and volcanism during January and February, and by DMS oxidation, Europe, east Asia, North America and west Asia/Siberia during March and April. Simulations of black carbon (BC) by Stohl et al (2013), Qi et al (2017) and Xu et al (2017) attribute 25-40 % of the winter BC and about 20 % of the spring BC at Alert to gas flaring in Russia, with eastern and southern Asia making contributions to the BC of about 20 % in January and about 40 % in April.…”