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Improving the ability of global models to predict concentrations of blackcarbon (BC) over the Pacific Ocean is essential to evaluate the impact of BCon marine climate. In this study, we tag BC tracers from 13 source regionsaround the globe in a global chemical transport model, Model for Ozone and Related Chemical Tracers,version 4 (MOZART-4). Numeroussensitivity simulations are carried out varying the agingtimescale of BCemitted from each source region. The aging timescale for each source regionis optimized by minimizing errors in vertical profiles of BC mass mixingratios between simulations and HIAPER Pole-to-Pole Observations (HIPPO). Formost HIPPO deployments, in the Northern Hemisphere, optimized agingtimescales are less than half a day for BC emitted from tropical andmidlatitude source regions and about 1 week for BC emitted from high-latitude regions in all seasons except summer. We find that East Asianemissions contribute most to the BC loading over the North Pacific, whileSouth American, African and Australian emissions dominate BC loadings overthe South Pacific. Dominant source regions contributing to BC loadings inother parts of the globe are also assessed. The lifetime of BC originatingfrom East Asia (i.e., the world's largest BC emitter) is found to be only2.2 days, much shorter than the global average lifetime of 4.9 days, makingthe contribution from East Asia to the global BC burden only 36 % of that from the secondlargest emitter, Africa. Thus, evaluating only relative emission rateswithout accounting for differences in aging timescales and deposition ratesis not predictive of the contribution of a given source region to climateimpacts. Our simulations indicate that the lifetime of BC increases nearlylinearly with aging timescale for all source regions. When the aging rate isfast, the lifetime of BC is largely determined by factors that control localdeposition rates (e.g., precipitation). The sensitivity of lifetime to agingtimescale depends strongly on the initial hygroscopicity of freshly emittedBC. Our findings suggest that the aging timescale of BC varies significantlyby region and season and can strongly influence the contribution of sourceregions to BC burdens around the globe. Therefore, improvingparameterizations of the aging process for BC is important for enhancing thepredictive skill of global models. Future observations that investigate theevolution of the hygroscopicity of BC as it ages from different source regionsto the remote atmosphere are urgently needed

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