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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 20
Atmos. Chem. Phys., 15, 11521–11535, 2015
https://doi.org/10.5194/acp-15-11521-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 11521–11535, 2015
https://doi.org/10.5194/acp-15-11521-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Oct 2015

Research article | 20 Oct 2015

Long-range transport of black carbon to the Pacific Ocean and its dependence on aging timescale

J. Zhang3,2,1, J. Liu1, S. Tao1, and G. A. Ban-Weiss3 J. Zhang et al.
  • 1Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing, China
  • 2School of Physics, Peking University, Beijing, China
  • 3Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, USA

Abstract. Improving the ability of global models to predict concentrations of black carbon (BC) over the Pacific Ocean is essential to evaluate the impact of BC on marine climate. In this study, we tag BC tracers from 13 source regions around the globe in a global chemical transport model, Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4). Numerous sensitivity simulations are carried out varying the aging timescale of BC emitted from each source region. The aging timescale for each source region is optimized by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Pole-to-Pole Observations (HIPPO). For most HIPPO deployments, in the Northern Hemisphere, optimized aging timescales are less than half a day for BC emitted from tropical and midlatitude source regions and about 1 week for BC emitted from high-latitude regions in all seasons except summer. We find that East Asian emissions contribute most to the BC loading over the North Pacific, while South American, African and Australian emissions dominate BC loadings over the South Pacific. Dominant source regions contributing to BC loadings in other parts of the globe are also assessed. The lifetime of BC originating from East Asia (i.e., the world's largest BC emitter) is found to be only 2.2 days, much shorter than the global average lifetime of 4.9 days, making the contribution from East Asia to the global BC burden only 36 % of that from the second largest emitter, Africa. Thus, evaluating only relative emission rates without accounting for differences in aging timescales and deposition rates is not predictive of the contribution of a given source region to climate impacts. Our simulations indicate that the lifetime of BC increases nearly linearly with aging timescale for all source regions. When the aging rate is fast, the lifetime of BC is largely determined by factors that control local deposition rates (e.g., precipitation). The sensitivity of lifetime to aging timescale depends strongly on the initial hygroscopicity of freshly emitted BC. Our findings suggest that the aging timescale of BC varies significantly by region and season and can strongly influence the contribution of source regions to BC burdens around the globe. Therefore, improving parameterizations of the aging process for BC is important for enhancing the predictive skill of global models. Future observations that investigate the evolution of the hygroscopicity of BC as it ages from different source regions to the remote atmosphere are urgently needed.

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Short summary
We tag BC emissions from 13 source regions around the globe in a global chemical transport model MOZART-4 and optimize the aging timescale for each source region by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Polo-to-Pole Observations (HIPPO). We find that the optimized aging timescale of BC varies significantly by region and season. Our simulations indicate that BC lifetime increases nearly linearly with aging timescale for all source regions.
We tag BC emissions from 13 source regions around the globe in a global chemical transport model...
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