Abstract
Abstract. Open biomass burning (OBB) has a high potential to trigger 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 in central and eastern China (CEC). This region includes nine provinces, i.e., Hubei, Anhui, Henan, Hunan, Jiangxi, Shandong, Jiangsu, Shanghai, and Fujian. The first four ones are located inland, while the others are on the eastern coast. However, uncertainties in current OCSB and other types of OBB emissions in chemical transport models (CTMs) lead to inaccuracies in evaluating their impacts on haze formations. Satellite retrievals provide an 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, nevertheless, generally underestimates their magnitudes due to unresolved small 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) over CEC. During this period, OBB was dominated by OCSB in terms of the number of fire hotspots and associated emissions (74 %–94 %), most of which were located at Henan and Anhui (> 60 %) with intensive enhancements from 5 to 14 June (> 80 %). OCSB generally exhibits a spatiotemporal correlation with regional haze over the central part of CEC (Henan, Anhui, Hubei, and Hunan), while other types of OBB emissions had influences on Jiangxi, Zhejiang, and Fujian. Based on these analyses, we establish a constraining method that integrates ground-level 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 allow the model to reproduce meteorological and chemical fields over CEC during the study period, whereas the 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 the OBB contributions were dominated by OCSB, especially in Henan, Anhui, Hubei, and Hunan, 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 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 impacted by areas (i.e., Henan and Anhui) enveloped in the high-pressure system. These results suggest that policymakers should strictly undertake interprovincial 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 reduce overestimates of bottom-up methods.
Highlights
IntroductionOpen biomass burning (OBB) has adverse impacts on ambient air quality and human health, owing to the fact that OBB generally emits abundant gaseous and particulate pollutants in a short period of time, carbonaceous aerosols (e.g., black carbon (BC) and organic carbon (OC); Li et al, 2010; Rose et al, 2010; Cheng et al, 2013, 2014; Ding et al, 2013; Saleh et al, 2014; Washenfelder et al, 2015; Vakkari et al, 2018; Bikkina et al, 2019)
With the evolution of meteorological patterns, Hubei and Hunan in the low-pressure system were impacted by areas (i.e., Henan and Anhui) enveloped in the high-pressure system. These results suggest that policymakers should strictly undertake interprovincial joint enforcement actions to prohibit irregular Open biomass burning (OBB), especially Open crop straw burning (OCSB) over central and eastern China (CEC)
We collected monthly OCSB and other types of OBB information estimated by FINNv1.5 over CEC throughout 2014
Summary
Open biomass burning (OBB) has adverse impacts on ambient air quality and human health, owing to the fact that OBB generally emits abundant gaseous and particulate pollutants in a short period of time, carbonaceous aerosols (e.g., black carbon (BC) and organic carbon (OC); Li et al, 2010; Rose et al, 2010; Cheng et al, 2013, 2014; Ding et al, 2013; Saleh et al, 2014; Washenfelder et al, 2015; Vakkari et al, 2018; Bikkina et al, 2019). It has been estimated that OBB contributes approximately 65 % to global annual average primary OC emissions (Bond et al, 2013) and more than 40 % to fine particulate matter (PM2.5) concentrations in specific cases of regional haze In China, estimated growth rates of BC, OC, and primary PM2.5 emitted by OBB from 2002 to 2016 were 180 %, 191 %, and 192 %, respectively (Mehmood et al, 2018), suggesting an urgent need to control OBB emissions. Previous studies showed that emissions from OCSB accounted for more than 80 % of those from OBB over China during the past decade. Emissions increased steadily during the past decade, thereby directly causing or substantially exacerbating regional haze (Wu et al, 2018)
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