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. Open biomass burning (OBB) has a high potential totrigger local and regional severe haze with elevated fine particulatematter (PM2.5) concentrations and could thus deteriorate ambient airquality and threaten human health. Open crop straw burning (OCSB), as acritical part of OBB, emits abundant gaseous and particulate pollutants,especially in fields with intensive agriculture, such as in central and easternChina (CEC). This region includes nine provinces, i.e., Hubei, Anhui, Henan, Hunan,Jiangxi, Shandong, Jiangsu, Shanghai, and Fujian. The first four ones arelocated inland, while the others are on the eastern coast. However,uncertainties in current OCSB and other types of OBB emissions in chemicaltransport models (CTMs) lead to inaccuracies in evaluating their impacts onhaze formations. Satellite retrievals provide an alternative that can beused to simultaneously quantify emissions of OCSB and other types of OBB,such as the Fire INventory from NCAR version 1.5 (FINNv1.5), which,nevertheless, generally underestimates their magnitudes due to unresolvedsmall fires. In this study, we selected June 2014 as our study period,which exhibited a complete evolution process of OBB (from 1 to 19 June) overCEC. During this period, OBB was dominated by OCSB in terms of the number offire hotspots and associated emissions (74 %–94 %), most ofwhich were located at Henan and Anhui (&gt; 60 %) with intensiveenhancements from 5 to 14 June (&gt; 80 %). OCSB generallyexhibits a spatiotemporal correlation with regional haze over the central partof CEC (Henan, Anhui, Hubei, and Hunan), while other types of OBB emissionshad influences on Jiangxi, Zhejiang, and Fujian. Based on these analyses, weestablish a constraining method that integrates ground-level PM2.5measurements with a state-of-art fully coupled regional meteorological andchemical transport model (the two-way coupled WRF-CMAQ) in order to deriveoptimal OBB emissions based on FINNv1.5. It is demonstrated that theseemissions allow the model to reproduce meteorological and chemical fieldsover CEC during the study period, whereas the original FINNv1.5underestimated OBB emissions by 2–7 times, depending onspecific spatiotemporal scales. The results show that OBB had substantialimpacts on surface PM2.5 concentrations over CEC. Most of the OBBcontributions were dominated by OCSB, especially in Henan, Anhui, Hubei, andHunan, while other types of OBB emissions also exerted an 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 show that the OCSB emissionsin Henan and Anhui can cause haze not only locally but also regionallythrough regional transport. Combining with meteorological analyses, we canfind that surface weather patterns played a cardinal role in reshapingspatial and temporal characteristics of PM2.5 concentrations.Stationary high-pressure systems over CEC enhanced local PM2.5concentrations in Henan and Anhui. Then, with the evolution ofmeteorological patterns, Hubei and Hunan in the low-pressure system wereimpacted by areas (i.e., Henan and Anhui) enveloped in the high-pressuresystem. These results suggest that policymakers should strictly undertakeinterprovincial joint enforcement actions to prohibit irregular OBB,especially OCSB over CEC. Constrained OBB emissions can, to a large extent,supplement estimations derived from satellite retrievals as well as reduceoverestimates of bottom-up methods.

atmospheric chemistry and physics

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