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| Titel |
Long-range transport of black carbon to the Pacific Ocean and its dependence on aging timescale |
| VerfasserIn |
J. Zhang, J. Liu, S. Tao, G. A. Ban-Weiss |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 20 ; Nr. 15, no. 20 (2015-10-20), S.11521-11535 |
| Datensatznummer |
250120103
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| Publikation (Nr.) |
 copernicus.org/acp-15-11521-2015.pdf |
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| Zusammenfassung |
| 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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