Night-Time Evolution and Vertical Distribution of Atmospheric Aerosols from the Largest Open Biomass Burning “Experiment” in Central Europe

<p><span>Open biomass burning (OBB) has large potential in triggering local and regional severe haze with elevated fine particulate matter (PM<sub>2.5</sub>) 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, uncertainties in current OCSB and other types of OBB emissions in </span><span>chemical transport models (CTMs) lead to inaccuracies in evaluating their impacts on haze formations. Satellite retrievals provide </span><span>an alternative that can be used to simultaneously quantify emissions of </span><span>OCSB and other types of OBB, such as </span><span>the Fire INventory from NCAR version 1.5 (FINNv1.5), which, nevertheless, 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, most of which were located at Henan and Anhui with intensive enhancements from June 5 to 14. OCSB generally exhibits 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 </span><span>ground-level PM<sub>2.5</sub> measurements with </span><span>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 PM<sub>2.5</sub> 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 influence in Jiangxi, Zhejiang, and Fujian. With the </span><span>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. </span><span>Combining with meteorological analyses, we can find that surface weather patterns played a cardinal role in reshaping spatial and temporal characteristics of PM<sub>2.5</sub> concentrations. Stationary high-pressure systems over CEC enhanced local PM<sub>2.5</sub> concentrations in Henan and Anhui. Then, with the evolution of meteorological patterns, Hubei and Hunan in the low-pressure system were impacted by areas 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.</span></p>

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.

Open biomass burning emissions and their contribution to ambient formaldehyde in Guangdong province, China.

Abstract. Air pollutant emissions from open biomass burning (OBB) in the Yangtze River Delta (YRD) were estimated for 2005–2015 using three (traditional bottom-up, fire radiative power (FRP), and constraining) approaches, and the differences among those methods and their sources were analyzed. The species included PM10, PM2.5, organic carbon (OC), elemental carbon (EC), CH4, non-methane volatile organic compounds (NMVOCs), CO, CO2, NOx, SO2 and NH3. The interannual trends in emissions with FRP-based and constraining methods were similar to the fire counts in 2005–2012, while those with the traditional method were not. For most years, emissions of all species estimated with the constraining method were smaller than those with the traditional method except for NMVOCs, while they were larger than those with the FRP-based method except for EC, CH4 and NH3. Such discrepancies result mainly from different masses of crop residue burned in the field (CRBF) estimated in the three methods. Chemistry transport modeling (CTM) was applied using the three OBB inventories. The simulated PM10 concentrations with constrained emissions were closest to the available observations, implying that the constraining method provided the best emission estimates. CO emissions in the three methods were compared with other studies. Similar temporal variations were found for the constrained emissions, FRP-based emissions, GFASv1.0 and GFEDv4.1s, with the largest and the lowest emissions estimated for 2012 and 2006, respectively. The temporal variations in the emissions based on the traditional method, GFEDv3.0, and the method of Xia et al. (2016) were different. The constrained CO emissions in this study were commonly smaller than those based on the traditional bottom-up method and larger than those based on burned area or FRP in other studies. In particular, the constrained emissions were close to GFEDv4.1s that contained emissions from small fires. The contributions of OBB to two particulate pollution events in 2010 and 2012 were analyzed with the brute-force method. Attributed to varied OBB emissions and meteorology, the average contribution of OBB to PM10 concentrations in 8–14 June 2012 was estimated at 37.6 % (56.7 µg m−3), larger than that in 17–24 June 2010 at 21.8 % (24.0 µg m−3). Influences of diurnal curves of OBB emissions and meteorology on air pollution caused by OBB were evaluated by designing simulation scenarios, and the results suggested that air pollution caused by OBB would become heavier if the meteorological conditions were unfavorable and that more attention should be paid to the OBB control at night. Quantified with Monte Carlo simulation, the uncertainty of the traditional bottom-up inventory was smaller than that of the FRP-based one. The percentages of CRBF and emission factors were the main source of uncertainty for the two approaches. Further improvement on CTM for OBB events would help better constrain OBB emissions.

Near-real-time estimation of hourly open biomass burning emissions in China using multiple satellite retrievals

Abstract. Open biomass burning (OBB) significantly affects regional and global air quality, the climate, and human health. The burning of forests, shrublands, grasslands, peatlands, and croplands influences OBB. A global emissions inventory based on satellite fire detection enables an accurate estimation of OBB emissions. In this study, we developed a global high-resolution (1 km×1 km) daily OBB emission inventory using the Chinese Fengyun-3D satellite's global fire spot monitoring data, satellite-derived biomass data, vegetation-index-derived spatiotemporally variable combustion efficiencies, and land-type-based emission factors. The average annual estimated OBB emissions for 2020–2022 were 2586.88 Tg C, 8841.45 Tg CO2, 382.96 Tg CO, 15.83 Tg CH4, 18.42 Tg NOx, 4.07 Tg SO2, 18.68 Tg particulate organic carbon (OC), 3.77 Tg particulate black carbon (BC), 5.24 Tg NH3, 15.85 Tg NO2, 42.46 Tg PM2.5 and 56.03 Tg PM10. Specifically, taking carbon emissions as an example, the average annual estimated OBBs for 2020–2022 were 72.71 (Boreal North America, BONA), 165.73 (Temperate North America, TENA), 34.11 (Central America, CEAM), 42.93 (Northern Hemisphere South America, NHSA), 520.55 (Southern Hemisphere South America, SHSA), 13.02 (Europe, EURO), 8.37 (Middle East, MIDE), 394.25 (Northern Hemisphere Africa, NHAF), 847.03 (Southern Hemisphere Africa, SHAF), 167.35 (Boreal Asia, BOAS), 27.93 (Central Asia, CEAS), 197.29 (Southeast Asia, SEAS), 13.20 (Equatorial Asia; EQAS), and 82.38 (Australia and New Zealand; AUST) Tg C yr−1. Overall, savanna grassland burning contributed the largest proportion of the annual total carbon emissions (1209.12 Tg C yr−1; 46.74 %), followed by woody savanna/shrubs (33.04 %) and tropical forests (12.11 %). SHAF was found to produce the most carbon emissions globally (847.04 Tg C yr−1), followed by SHSA (525.56 Tg C yr−1), NHAF (394.26 Tg C yr−1), and SEAS (197.30 Tg C yr−1). More specifically, savanna grassland burning was predominant in SHAF (55.00 %, 465.86 Tg C yr−1), SHSA (43.39 %, 225.86 Tg C yr−1), and NHAF (76.14 %, 300.21 Tg C yr−1), while woody savanna/shrub fires were dominant in SEAS (51.48 %, 101.57 Tg C yr−1). Furthermore, carbon emissions exhibited significant seasonal variability, peaking in September 2020 and August of 2021 and 2022, with an average of 441.32 Tg C month−1, which is substantially higher than the monthly average of 215.57 Tg C month−1. Our comprehensive high-resolution inventory of OBB emissions provides valuable insights for enhancing the accuracy of air quality modeling, atmospheric transport, and biogeochemical cycle studies. The GEIOBB dataset can be downloaded at http://figshare.com (last access: 30 July 2024) with the following DOI: https://doi.org/10.6084/m9.figshare.24793623.v2 (Liu et al., 2023).

Open biomass burning (OBB) is a significant source of air pollutants and greenhouse gases that have contributed to air pollution episodes in China in recent years. An accurate emission inventory is critical for the precise control of OBB. Existing OBB emission datasets are commonly based on MODIS observations, and most only have a daily-scale temporal resolution. Daily OBB emissions, however, might not accurately represent diurnal variations, peak hours, or any open burning processes. The China Hourly Open Biomass Burning Emissions (CHOBE) dataset for mainland China from 2016 to 2020 was developed in this study using the spatiotemporal fusion of multiple active fires from MODIS, VIIRS S-NPP and Himawari-8 AHI detections. At a spatial resolution of 2 km, CHOBE provided gridded CO, NOx, SO2, NH3, VOCs, PM2.5, CO2, CH4 and N2O emissions from OBB. CHOBE will enhance insight into OBB spatiotemporal variability, improves air quality and climate modelling and forecasting, and aids in the formulation of precise OBB preventive and control measures.

Open biomass burning (OBB) with a main contribution from open crop straw burning (OCSB) plays a key role in the formation of heavy haze episodes during harvest seasons in China through release of particulate matter (PM) and gaseous pollutants. Here we analyze spatial and temporal distributions of air pollutant emissions from OCSB and OBB in China from 2002 to 2016 on the basis of daily and highly resolved (1 km) emissions from the latest FINNv1.5 inventory. Estimated annual emissions of black carbon, organic carbon, PM_(2.5), PM_(10), CH_4, CO, CO_2, NH_3, NO_x, SO_2 and NMVOCS from OBB in China from 2002 to 2016 have increased by 192, 180, 191, 196, 212, 199, 173, 208, 185, 184 and 225%, respectively, whereas emissions from OCSB have increased consistently by ~ 200% for each species. Estimated PM_(2.5) annual emissions from OCSB increased significantly by 245.7% from 14.9 Gg/year in 2012 to 51.5 Gg/year in 2016 in Northeast China, whereas decreasing by 76.1% from 76.3 Gg/year in 2012 to 18.2 Gg/year in 2016 in East China. Contributions of OCSB in OBB emissions increased from 25.4% in 2002 to 56.4% in 2016 in North China and from 31.0% in 2002 to 66.4% in 2016 in Northeast China. Spatial distributions for the period of 2002-2016 indicate that the largest PM_(2.5) annual mean emissions from OCSB (37.0 Gg/year) occur in East China, followed by Northeast China (20.0 Gg/year) and Central China (13.5 Gg/year), whereas Southwest China has the largest PM_(2.5) annual mean emissions from OBB (286.5 Gg/year), following by East China (273.7 Gg/year), South China (237.3 Gg/year) and Central China (126.1 Gg/year). Contributions of OCSB in OBB emissions for PM_(2.5) have increased significantly to 56.4–66.4% in North and Northeast China in 2016.

Development of 1 ×1 km gridded emission inventory for air quality assessment and mitigation strategies from open biomass burning in Karnataka, India

High-resolution and multi-year estimation of emissions from open biomass burning in Northeast China during 2001–2017

Observational insights into the environmental effect for secondary inorganic aerosol formation in the Northeast China: Influence of biomass burning

Brown carbon (BrC) is a type of organic carbon with light-absorbing abilities, especially in ultraviolet (UV) radiation, which could significantly contribute to global warming. Observations have shown high BrC concentrations and absorption in China, suggesting potentially large BrC emissions. The potential contribution of fossil fuel combustion to BrC emission has been ignored in most previous studies. Here, we use GEOS-Chem to simulate BrC distribution and absorption in China, accounting for three major primary BrC sources: residential coal and biofuel combustion, vehicle exhausts, and open biomass burning. Based on the literature and related energy consumption data, we estimate the specific emission ratio of BrC versus BC, and BrC mass absorption efficiency (MAE) for each source. Combined with BC emission, total BrC emission in China is then estimated to be 3.42 Tg yr−1 in 2018, of which 71% is from residential combustion, 14% is from vehicle exhaust, and 15% is from open biomass burning. Residential combustion is the main source of surface BrC in China, accounting for 60% on average, followed by open biomass burning (23%) and vehicle exhaust emissions (17%). There is a clear seasonality in surface BrC concentrations with the maximum in winter (5.1 µg m−3), followed by spring (2.8 µg m−3), autumn (2.3 µg m−3), and summer (1.3 µg m−3). BrC AAOD at 365 nm ranges from 0.0017 to 0.060 in China, mainly dominated by residential combustion (73%), followed by open biomass burning (16%), and vehicle exhaust emissions (11%). It is also estimated that BrC accounts for 45–67% (52% on average) of total carbonaceous aerosol AAOD at 365 nm, implying an equal importance of BrC and BC regarding the absorption in UV radiation.

Greater Cairo, the most populous megacity in the Middle East North Africa (MENA) region, faces severe aerosol pollution, posing a significant threat to public health. Despite its impact, the main sources of pollution remain under-characterized due to sparse atmospheric observations. To address this gap, we conducted a continuous two-month field study at an urban background site, documenting the first chemical and physical properties of submicron aerosols (PM1). We found that crustal material from both desert dust and traffic dust resuspension accounted for as much as 24% of the total PM1 mass, increasing to 66% during desert dust events—a level unusually high for urban settings. Simultaneously, our data indicated reductions in black carbon and ammonium sulfate levels, suggesting successful emission reductions through local and regional mitigation efforts. The diurnal patterns of carbonaceous aerosols were linked to peak emissions from local traffic during rush hours and from open biomass burning at night. Contrarily, our analysis identified unexpectedly high levels of semi-volatile ammonium chloride (NH4Cl) from local open biomass and waste burning, emerging as the predominant PM1 chemical species in Cairo. Its formation at night significantly influenced morning aerosol water uptake, thereby playing a crucial role in the formation of persistent urban haze. These findings not only confirm the ongoing presence of a significant dust reservoir over Cairo but also reveal a new source of highly hygroscopic semi-volatile inorganic salts, leading to a unique type of urban haze. This haze, characterized by major contributions from both submicron and supermicron particle modes, highlights the complex implications of heterogeneous chemical transformations of air pollutants in urban settings, emphasizing the need for interdisciplinary research to understand and mitigate these impacts in the Mediterranean and similar regions. Full details are available in our publication in Christodoulou et al., 2024.Christodoulou, A., Bezantakos, S., Bourtsoukidis, E., Stavroulas, I., Pikridas, M., Oikonomou, K., Iakovides, M., Hassan, S. K., Boraiy, M., El-Nazer, M., Wheida, A., Abdelwahab, M., Sarda-Estève, R., Rigler, M., Biskos, G., Afif, C., Borbon, A., Vrekoussis, M., Mihalopoulos, N., Sauvage, S., and Sciare, J.: Submicron aerosol pollution in Greater Cairo (Egypt): A new type of urban haze?, Environ. Int., 186, https://doi.org/10.1016/j.envint.2024.108610, 2024.

Abstract. Open biomass burning (OBB) has significant impacts on air pollution, climate change and potential human health. OBB has gathered wide attention but with little focus on the annual variation of pollutant emission. Central and eastern China (CEC) is one of the most polluted regions in China. This study aims to provide a state-of-the-art estimation of the pollutant emissions from OBB in CEC from 2003 to 2015, by adopting the satellite observation dataset – the burned area product (MCD64Al) and the active fire product (MCD14 ML) – along with local biomass data (updated biomass loading data and high-resolution vegetation data) and local emission factors. The successful adoption of the double satellite dataset for long-term estimation of pollutants from OBB with a high spatial resolution can support the assessing of OBB on regional air quality, especially for harvest periods or dry seasons. It is also useful to evaluate the effects of annual OBB management policies in different regions. Here, monthly emissions of pollutants were estimated and allocated into a 1×1 km spatial grid for four types of OBB including grassland, shrubland, forest and cropland. From 2003 to 2015, the emissions from forest, shrubland and grassland fire burning had an annual fluctuation, whereas the emissions from crop straw burning steadily increased. The cumulative emissions of organic carbon (OC), elemental carbon (EC), methane (CH4), nitric oxide (NOx), non-methane volatile organic compounds (NMVOCs), sulfur dioxide (SO2), ammonia (NH3), carbon monoxide (CO), carbon dioxide (CO2) and fine particles (PM2.5) were 3.64×103, 2.87×102, 3.05×103, 1.82×103, 6.4×103, 2.12×102, 4.67×102, 4.59×104, 9.39×105 and 4.13×103 Gg in these years, respectively. Crop straw burning was the largest contributor for all pollutant emissions, by 84 %–96 %. For the forest, shrubland and grassland fire burning, forest fire burning emissions contributed the most, and emissions from grassland fire were negligible due to little grass coverage in this region. High pollutant emissions concentrated in the connection area of Shandong, Henan, Jiangsu and Anhui, with emission intensity higher than 100 tons per square kilometer, which was related to the frequent agricultural activities in these regions. Peak emission of pollutants occurred during summer and autumn harvest periods including May, June, September and October, during which ∼50 % of the total pollutant emissions were emitted in these months. This study highlights the importance of controlling the crop straw burning emissions. From December to March, the crop residue burning emissions decreased, while the emissions from forest, shrubland and grassland exhibited their highest values, leading to another small peak in emissions of pollutants. Obvious regional differences in seasonal variations of OBB were observed due to different local biomass types and environmental conditions. Rural population, agricultural output, economic levels, local burning habits, social customs and management policies were all influencing factors for OBB emissions.

Underestimated contribution of open biomass burning to terpenoid emissions revealed by a novel hourly dynamic inventory