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Discussion papers
https://doi.org/10.5194/acp-2019-808
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-808
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 17 Oct 2019

Submitted as: research article | 17 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Relative effects of open biomass and crop straw burning on haze formation over central and eastern China: modelling study driven by constrained emissions

Khalid Mehmood1,*, Yujie Wu1,*, Liqiang Wang1, Shaocai Yu1,2, Pengfei Li1,3, Xue Chen1, Zhen Li1, Yibo Zhang1, Mengying Li1, Weiping Liu1, Yannian Zhu4, Daniel Rosenfeld5, and John H. Seinfeld2 Khalid Mehmood et al.
  • 1Research Center for Air Pollution and Health; Key Laboratory of Environmental Remediation and Ecological Health, Ministry of Education, College of Environment and Resource Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, P.R. China
  • 2Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
  • 3College of Science and Technology, Hebei Agricultural University, Baoding, Hebei 071000, P.R. China
  • 4Meteorological Institute of Shaanxi Province, 36 Beiguanzhengjie, Xi’an 710015, China
  • 5Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • *These authors contributed equally to this work.

Abstract. Open biomass burning (OBB) has large potential in triggering local and regional severe haze with elevated fine particulate matter (PM2.5) concentrations and could thus deteriorate ambient air quality and threaten human health. Open crop straw burning (OCSB), as a critical part of OBB, emits abundant gaseous and particulate pollutants, especially in fields with intensive agriculture, such as central and eastern China (CEC). However, there are high uncertainties in current OCSB and other types of OBB emissions that could drive chemical transport models (CTMs) to fail to evaluate their respective impacts on haze formations accurately. Satellite retrievals provide an attractive alternative that can be used to simultaneously quantify emissions of OCSB and other types of OBB, such as the Fire INventory from NCAR version 1.5 (FINNv1.5), which yet generally underestimate their magnitudes due to unresolved small fires. In this study, we selected June in 2014 as our study period, which exhibited a complete evolution process of OBB (from June 1 to 19) over CEC. During this period, OBB was dominated by OCSB in terms of the number of fire hotspot and associated emissions (74 ~ 94 %), most of which were located at Henan and Anhui (> 60 %) with intensive enhancements from June 5 to 14 (> 80 %). It is found that OCSB presented a generally strong spatiotemporal correlation with regional haze over the central part of CEC (Henan, Anhui, Hubei, and Hunan), while other types of OBB emissions had certain influences on Jiangxi, Zhejiang, and Fujian. Based on these analyses, we established a constraining method that integrates ground PM2.5 measurements with a state-of-art fully coupled regional meteorological and chemical transport model (the two-way coupled WRF-CMAQ) in order to derive optimal OBB emissions based on FINNv1.5. It is demonstrated that these emissions could allow the model to reproduce meteorological and chemical fields over CEC during the study period, whereas original FINNv1.5 underestimated OBB emissions by 2 ~ 7 times, depending on specific spatiotemporal scales. The results show that OBB had substantial impacts on surface PM2.5 concentrations over CEC. Most of OBB contributions were dominated by OCSB, especially in Henan, Anhui, Hubei, and Hunan, while other types of OBB emissions also exerted certain influence in Jiangxi, Zhejiang, and Fujian. With the concentration-weighted trajectory (CWT) method, potential OCSB sources leading to severe haze in Henan, Anhui, Hubei, and Hunan were pinpointed. The results illustrated that the OCSB emissions in Henan and Anhui can cause haze not only locally but also regionally through regional transport. Combining with meteorological analyses, we can find that surface weather patterns played a cardinal role in reshaping spatial and temporal characteristics of PM2.5 concentrations. Stationary high-pressure systems over CEC enhanced local PM2.5 concentrations in Henan and Anhui. Then, with the evolution of meteorological patterns, Hubei and Hunan in the low-pressure system were forced to receive the pollution from areas (i.e., Henan and Anhui) enveloped in the high-pressure system. These results highlight that policymakers should strictly undertake interprovincial joint enforcement actions to prohibit irregular OBB, especially OCSB over CEC. By comparison, the constrained OBB emissions can, to a large extent, not only supplement insufficient estimations derived from satellite retrievals but also reduce overestimations of bottom-up methods.

Khalid Mehmood et al.
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Short summary
We selected June in 2014 as our study period, which exhibited a complete evolution process of Open biomass burning (OBB) dominated by Open crop straw burning (OCSB) over central and eastern China (CEC). We established a constraining method that integrates ground PM2.5 measurements with the two-way coupled WRF-CMAQ to derive optimal OBB emissions. It is found that these emissions could allow the model to reproduce meteorological and chemical fields over CEC during the study period.
We selected June in 2014 as our study period, which exhibited a complete evolution process of...
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