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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-801
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
21 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Sources and physicochemical characteristics of black carbon aerosol in the southeastern Tibetan Plateau: internal mixing enhances light absorption
Qiyuan Wang1, Junji Cao1,2, Yongming Han1,3, Jie Tian4, Chongshu Zhu1, Yonggang Zhang1, Ningning Zhang1, Zhenxing Shen4, Haiyan Ni1, Shuyu Zhao1, and Jiarui Wu1 1Key Laboratory of Aerosol Chemistry and Physics, State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China
2Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, 710049, China
3School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
4Department of Environmental Sciences and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
Abstract. Black carbon (BC) aerosol over the Tibetan Plateau (TP) has important effects on regional climate and hydrological processes. An intensive measurement campaign was conducted at Lulang (~ 3300 m above sea level), southeastern TP, from September to October 2015 to investigate the sources and physicochemical characteristics of refractory BC (rBC) aerosol. The grand average rBC mass concentration was 0.31 ± 0.55 μg m−3, which is higher than most BC results for the TP. A clear diurnal cycle in rBC showed high values in the morning and low values in the afternoon. A bivariate polar plot showed that rBC loadings were affected by wind speed and direction, and it was used to infer the dominant transport directions. The estimated net surface transport intensity for rBC was +0.05 ± 0.29 μg s−1 m−2, indicating that stronger transport from outside the TP compared with the interior of the TP. Cluster analysis and a concentration-weighted trajectory model indicated that emissions from north India had important contribution to the high rBC, but the effects of internal TP sources cannot be overlooked. The average mass median diameter (MMD) of rBC was 160 ± 23 nm, and it was smaller size on rainy days (145 nm) compared with non-rainy days (164 nm). The average number fraction of thickly-coated rBC (FrBC) was 39 ± 8%, and it increased with the enhanced O3 mixing ratio from 10:00–14:00 local time, indicating that the photochemical oxidation played an important role in forming rBC coatings. The slope of a linear regression of FrBC versus O3 was 0.44 % ppb−1, which was higher than the value of 0.24 % ppb−1 observed at Qinghai Lake, northeastern TP, suggesting that the rBC particles at Lulang were more rapidly affected by internal mixing than those at Qinghai Lake. The average rBC absorption enhancement (Eabs) was estimated to be 1.8, suggesting that light absorption by coated rBC particles was greater than that for the uncoated ones. The Eabs was strongly positively correlated with the FrBC, indicating an amplification of light absorption for internally-mixed rBC. When rBC core < 170 nm, the Eabs was negatively correlated with MMD, but it was nearly constant for rBC core > 170 nm. Our study provides insight into the sources and evolution of rBC aerosol in the TP, and is useful for further modelling studies improving precise of evaluating the radiative forcing of carbonaceous aerosols in this area.

Citation: Wang, Q., Cao, J., Han, Y., Tian, J., Zhu, C., Zhang, Y., Zhang, N., Shen, Z., Ni, H., Zhao, S., and Wu, J.: Sources and physicochemical characteristics of black carbon aerosol in the southeastern Tibetan Plateau: internal mixing enhances light absorption, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-801, in review, 2017.
Qiyuan Wang et al.
Qiyuan Wang et al.
Qiyuan Wang et al.

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