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We quantify source contributions to springtime (April 2008) surface blackcarbon (BC) in the Arctic by interpreting surface observations of BC at fivereceptor sites (Denali, Barrow, Alert, Zeppelin, and Summit) using a globalchemical transport model (GEOS-Chem) and its adjoint. Contributions to BC atBarrow, Alert, and Zeppelin are dominated by Asian anthropogenic sources(40–43 %) before 18 April and by Siberian open biomass burning emissions(29–41 %) afterward. In contrast, Summit, a mostly free troposphericsite, has predominantly an Asian anthropogenic source contribution(24–68 %, with an average of 45 %). We compute the adjointsensitivity of BC concentrations at the five sites during a pollution episode(20–25 April) to global emissions from 1 March to 25 April. The associatedcontributions are the combined results of these sensitivities and BCemissions. Local and regional anthropogenic sources in Alaska are the largestanthropogenic sources of BC at Denali (63 % of total anthropogeniccontributions), and natural gas flaring emissions in the western extremenorth of Russia (WENR) are the largest anthropogenic sources of BC atZeppelin (26 %) and Alert (13 %). We find that long-range transportof emissions from Beijing–Tianjin–Hebei (also known as Jing–Jin–Ji), thebiggest urbanized region in northern China, contribute significantly (∼ 10 %)</span> to surfaceBC across the Arctic. On average, it takes ∼ 12 days for Asiananthropogenic emissions and Siberian biomass burningemissions to reach the Arctic lower troposphere, supporting earlier studies.Natural gas flaring emissions from the WENR reach Zeppelin in about a week.We find that episodic transport events dominate BC at Denali (87 %), a siteoutside the Arctic front, which is a strong transport barrier. The relativecontribution of these events to surface BC within the polar dome is muchsmaller (∼ 50 % at Barrow and Zeppelin and ∼ 10 % at Alert).The large contributions from Asian anthropogenic sourcesare predominately in the form of <q>chronic</q> pollution (∼ 40 %at Barrow, 65 % at Alert, and 57 % at Zeppelin) on about a 1-monthtimescale. As such, it is likely that previous studies using 5- or 10-daytrajectory analyses strongly underestimated the contribution from Asia tosurface BC in the Arctic

Sources of springtime surface black carbon in the Arctic: an adjoint analysis for April 2008