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Volume 17, issue 15 | Copyright
Atmos. Chem. Phys., 17, 9697-9716, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Aug 2017

Research article | 15 Aug 2017

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

Ling Qi1,2, Qinbin Li1,2, Daven K. Henze3, Hsien-Liang Tseng1,2, and Cenlin He1,2 Ling Qi et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USA
  • 2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA
  • 3Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA

Abstract. We quantify source contributions to springtime (April 2008) surface black carbon (BC) in the Arctic by interpreting surface observations of BC at five receptor sites (Denali, Barrow, Alert, Zeppelin, and Summit) using a global chemical transport model (GEOS-Chem) and its adjoint. Contributions to BC at Barrow, 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 tropospheric site, has predominantly an Asian anthropogenic source contribution (24–68%, with an average of 45%). We compute the adjoint sensitivity of BC concentrations at the five sites during a pollution episode (20–25 April) to global emissions from 1 March to 25 April. The associated contributions are the combined results of these sensitivities and BC emissions. Local and regional anthropogenic sources in Alaska are the largest anthropogenic sources of BC at Denali (63% of total anthropogenic contributions), and natural gas flaring emissions in the western extreme north of Russia (WENR) are the largest anthropogenic sources of BC at Zeppelin (26%) and Alert (13%). We find that long-range transport of emissions from Beijing–Tianjin–Hebei (also known as Jing–Jin–Ji), the biggest urbanized region in northern China, contribute significantly (∼10%) to surface BC across the Arctic. On average, it takes ∼12 days for Asian anthropogenic emissions and Siberian biomass burning emissions 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 site outside the Arctic front, which is a strong transport barrier. The relative contribution of these events to surface BC within the polar dome is much smaller (∼ 50% at Barrow and Zeppelin and ∼10% at Alert). The large contributions from Asian anthropogenic sources are predominately in the form of chronic pollution (∼40% at Barrow, 65% at Alert, and 57% at Zeppelin) on about a 1-month timescale. As such, it is likely that previous studies using 5- or 10-day trajectory analyses strongly underestimated the contribution from Asia to surface BC in the Arctic.

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We find that Asian anthropogenic sources are the largest contributors (~ 40 %) to surface BC in spring in the Arctic, inconsistent with previous studies which repeatedly identified sources of surface BC as anthropogenic emissions from Europe and Russia. It takes 12–17 days for Asian anthropogenic emissions to be transported to the Arctic surface. Additionally, a large fraction (40–65 %) of Asian contribution is in the form of chronic pollution on 1- to 2-month timescales.
We find that Asian anthropogenic sources are the largest contributors (~ 40 %) to surface BC in...