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An unexpected catalyst dominates formation and radiative forcing of regional haze

Zhang, Fang and Wang, Yuan and Peng, Jianfei and Chen, Lu and Sun, Yele and Duan, Lian and Ge, Xinlei and Li, Yixin and Zhao, Jiayun and Liu, Chao and Zhang, Xiaochun and Zhang, Gen and Pan, Yuepeng and Wang, Yuesi and Zhang, Annie L. and Ji, Yuemeng and Wang, Gehui and Hu, Min and Molina, Mario J. and Zhang, Renyi (2020) An unexpected catalyst dominates formation and radiative forcing of regional haze. Proceedings of the National Academy of Sciences of the United States of America, 117 (8). pp. 3960-3966. ISSN 0027-8424. PMCID PMC7049161.

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Although regional haze adversely affects human health and possibly counteracts global warming from increasing levels of greenhouse gases, the formation and radiative forcing of regional haze on climate remain uncertain. By combining field measurements, laboratory experiments, and model simulations, we show a remarkable role of black carbon (BC) particles in driving the formation and trend of regional haze. Our analysis of long-term measurements in China indicates declined frequency of heavy haze events along with significantly reduced SO₂, but negligibly alleviated haze severity. Also, no improving trend exists for moderate haze events. Our complementary laboratory experiments demonstrate that SO₂ oxidation is efficiently catalyzed on BC particles in the presence of NO₂ and NH₃, even at low SO₂ and intermediate relative humidity levels. Inclusion of the BC reaction accounts for about 90–100% and 30–50% of the sulfate production during moderate and heavy haze events, respectively. Calculations using a radiative transfer model and accounting for the sulfate formation on BC yield an invariant radiative forcing of nearly zero W m⁻² on the top of the atmosphere throughout haze development, indicating small net climatic cooling/warming but large surface cooling, atmospheric heating, and air stagnation. This BC catalytic chemistry facilitates haze development and explains the observed trends of regional haze in China. Our results imply that reduction of SO₂ alone is insufficient in mitigating haze occurrence and highlight the necessity of accurate representation of the BC chemical and radiative properties in predicting the formation and assessing the impacts of regional haze.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Wang, Yuan0000-0001-6657-8401
Sun, Yele0000-0003-2354-0221
Liu, Chao0000-0001-7049-493X
Pan, Yuepeng0000-0002-5547-0849
Molina, Mario J.0000-0003-2339-3225
Zhang, Renyi0000-0001-8708-3862
Additional Information:© 2020 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). Contributed by Mario J. Molina, December 24, 2019 (sent for review November 7, 2019; reviewed by Russell R. Dickerson and Manish Shrivastava). PNAS first published February 10, 2020. This work was supported by the National Natural Science Foundation of China (Grants 41675141 and 41975174), the National Basic Research Program of China (Grant 2017YFC1501702), and the Robert A. Welch Foundation (Grant A-1417). We thank Zipeng Dong for assistance with the radiative forcing data analysis. Data and Materials Availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the SI Appendix. Additional data related to this paper may be requested from the authors. Author contributions: F.Z. and R.Z. designed research; F.Z., Yuan Wang, J.P., L.C., Y.S., and R.Z. performed research; X.G., X.Z., G.Z., Y.P., Yuesi Wang, M.H., and M.J.M. contributed new reagents/analytic tools; F.Z., J.P., Y.S., L.D., Y.L., J.Z., C.L., Y.J., G.W., and M.J.M. analyzed data; and F.Z., A.L.Z., and R.Z. wrote the paper. Reviewers: R.R.D., University of Maryland; and M.S., Pacific Northwest National Laboratory. The authors declare no competing interest. This article contains supporting information online at
Funding AgencyGrant Number
National Natural Science Foundation of China41675141
National Natural Science Foundation of China41975174
National Basic Research Program of China2017YFC1501702
Robert A. Welch FoundationA-1417
Subject Keywords:black carbon; air pollution; climate; multiphase chemistry; haze
Issue or Number:8
PubMed Central ID:PMC7049161
Record Number:CaltechAUTHORS:20200211-073547438
Persistent URL:
Official Citation:An unexpected catalyst dominates formation and radiative forcing of regional haze. Fang Zhang, Yuan Wang, Jianfei Peng, Lu Chen, Yele Sun, Lian Duan, Xinlei Ge, Yixin Li, Jiayun Zhao, Chao Liu, Xiaochun Zhang, Gen Zhang, Yuepeng Pan, Yuesi Wang, Annie L. Zhang, Yuemeng Ji, Gehui Wang, Min Hu, Mario J. Molina, Renyi Zhang. Proceedings of the National Academy of Sciences Feb 2020, 117 (8) 3960-3966; DOI: 10.1073/pnas.1919343117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101216
Deposited By: Tony Diaz
Deposited On:11 Feb 2020 16:58
Last Modified:10 Mar 2020 17:24

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