High-resolution inventory of mercury emissions from biomass burning in tropical continents during 2001-2017

High-precision spatio-temporal variations and future perspectives of multiple air pollutant emissions from Chinese biomass-fired industrial boilers

Biomass-fired industrial boilers (BFIBs) are one of the neglected and important anthropogenic sources of air pollutants. A comprehensive boiler-based emission inventory of multiple air pollutants from BFIBs in China in 2020 was first developed based on the activity level database and updated emission factors. Results showed that national emissions of air pollutants from BFIBs in 2020 were estimated to be 11.5 kt of PM, 10.8 kt of PM10, 7.4 kt of PM2.5, 40.5 kt of SO2, 79.8 kt of NOx, 4.2 kt of organic carbon (OC), 1.0 kt of elemental carbon (EC), 31.7 kt of nonmethane volatile organic compounds (NMVOCs), 15.9 kt of NH3, and 116.5 t of five trace metals (Hg, Cr, Cd, Pb, and As), respectively. Air pollutant emissions exhibited significant spatio-temporal heterogeneity. Monthly air pollutant emissions varied by geographical division due to the combined effects of industrial production and winter heating demand. These emissions were mainly concentrated in the eastern coastal region, with Guangdong, Guangxi, Fujian, Jiangsu, and Zhejiang being the five provinces having the highest emissions. In addition, scenario predictions indicate that as the pollution and carbon reduction strategy is implemented, air pollutant emissions from BFIBs in China could become well controlled, with PM, NOx, SO2, and Hg emissions in 2050 projected to be 3.0-8.3 kt, 36.5-75.7 kt, 16.2-32.8 kt, and 0.52-0.87 t, respectively. Our results can provide a highly spatio-temporal resolution inventory of multiple air pollutant emissions from BFIBs for air quality modelling and support the formulation of air pollution control policies for biomass fuel utilization in the context of the pollution and carbon reduction strategy.

Estimation of mercury uptake and distinction of corn cultivation in China

Corn cultivation potentially plays a vital role in the global mercury (Hg) biogeochemical cycle. Nevertheless, there have been limited studies quantifying the Hg mass flow during corn cultivation. This study focuses on Hg uptake by corn plants in China, integrating data from both sample collection and prior studies, resulting in 400 datasets. The findings reveal that the Hg in corn plants is mainly incorporated in leaves (45.5 %-47.5 %) and husks (14.5 %-15.7 %). Despite a decrease in total gaseous Hg (TGM) concentrations in the atmosphere over time, annual Hg uptake by corn cultivation in China has risen from 72.0 (ranging from 47.6 to 96.3) tons (2009-2014) to 84.3 (ranging from 51.9 to 109.6) tons (2015-2020) due to the increasing in corn kernel production. Spatial analysis demonstrates regional disparities in Hg uptake, primarily influenced by corn kernel production, TGM levels, and soil Hg content. Furthermore, temporal analysis reveals a shift in the fate of Hg in corn plants, which can be attributed to variations in corn straw treatment policy or methods. From 2009 to 2014, a substantial amount of absorbed Hg by corn plants was re-released into the atmosphere (48.9 %) due to corn residues burning, whereas, between 2015 and 2020, a greater proportion of Hg ended up accumulating in the soil (51.1 %) after the imposition of the straw burning ban in China. Prior to the ban (2009-2014), corn cultivation contributed approximately 7.7 tons of Hg input to soil annually, with a range from 1.7 to 13.5. However, following the ban (2015-2020), Hg input into the soil increased by approximately 4.5 times, reaching 34.5 (ranging from 17.5 to 52.6) tons per year. These findings emphasize the significant risks associated with soil Hg pollution caused by corn cultivation due to the straw burning ban.

Mercury in Neotropical birds: a synthesis and prospectus on 13 years of exposure data

Environmental mercury (Hg) contamination of the global tropics outpaces our understanding of its consequences for biodiversity. Knowledge gaps of pollution exposure could obscure conservation threats in the Neotropics: a region that supports over half of the world's species, but faces ongoing land-use change and Hg emission via artisanal and small-scale gold mining (ASGM). Due to their global distribution and sensitivity to pollution, birds provide a valuable opportunity as bioindicators to assess how accelerating Hg emissions impact an ecosystem's ability to support biodiversity, and ultimately, global health. We present the largest database on Neotropical bird Hg concentrations (n = 2316) and establish exposure baselines for 322 bird species spanning nine countries across Central America, South America, and the West Indies. Patterns of avian Hg exposure in the Neotropics broadly align with those in temperate regions: consistent bioaccumulation across functional groups and high spatiotemporal variation. Bird species occupying higher trophic positions and aquatic habitats exhibited elevated Hg concentrations that have been previously associated with reductions in reproductive success. Notably, bird Hg concentrations were over four times higher at sites impacted by ASGM activities and differed by season for certain trophic niches. We developed this synthesis via a collaborative research network, the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative, which exemplifies inclusive, equitable, and international data-sharing. While our findings signal an urgent need to assess sampling biases, mechanisms, and consequences of Hg exposure to tropical avian communities, the TRACE Initiative provides a meaningful framework to achieve such goals. Ultimately, our collective efforts support and inform local, scientific, and government entities, including Parties of the United Nations Minamata Convention on Mercury, as we continue working together to understand how Hg pollution impacts biodiversity conservation, ecosystem function, and public health in the tropics.

Impact of forest fire on the mercury stable isotope composition in litter and soil in the Amazon

Mercury (Hg) emissions from forest fires, especially tropical forests such as the Amazonian forest, were shown to contribute significantly to the atmospheric mercury budget, but new methods are still necessary to improve the traceability and to reduce the great uncertainties related to this emission source. Recent studies have shown that the combustion process can result in Hg stable isotope fractionation that allows tracking coal combustion Hg emissions, as influenced by different factors such as combustion temperature. The main goal of the present study was, therefore, to investigate for the first time the potential of Hg stable isotopes to trace forest fire Hg emissions and pathways. More specifically, small-scale and a large scale prescribed forest fire experiments were conducted in the Brazilian Amazonian forest to study the impact of fire severity on Hg isotopic composition of litter, soil, and ash samples and associated Hg isotope fractionation pathways. In the small-scale experiment, no difference was found in the mercury isotopic composition of the samples collected before and after burning. In contrast, the larger-scale experiment resulted in significant mass dependent fractionation (MDF δ202Hg) in soils and ash suggesting that higher combustion temperature influence Hg isotopic fractionation with the emission of lighter Hg isotopes to the atmosphere and enrichment with heavier Hg in ashes. As for coal combustion, mass independent fractionation was not observed. To our knowledge, these results are the first to highlight the potential of forest fires to cause Hg isotopic fractionation, depending on the fire severity. The results also allowed to establish an isotopic fingerprint for tropical forest fire Hg emissions that corresponds to a mixture of litter and soil Hg isotopic composition (resulting atmospheric δ202Hg, Δ200Hg and Δ199Hg were -1.79 ± 0.24‰, -0.05 ± 0.04‰ and -0.45 ± 0.12‰, respectively).

High-resolution atmospheric mercury emission from open biomass burning in China: Integration of localized emission factors and multi-source finer resolution remote sensing data

Mercury (Hg) emissions from open biomass burning represent one of the largest Hg inputs to the atmosphere, with considerable effects on the atmospheric Hg budget. However, there is currently large uncertainty in the inventory of Hg emissions from open biomass burning in China due to limitations on the coarse resolution of burned area products, rough biomass data, and the unavailability of suitable emission factors (EFs). In this study, we developed high tempo-spatial resolution (30 m) and long time-series (2000-2019) atmospheric Hg emission inventories from open biomass burning using the Global Annual Burned Area Map (GABAM) product, high-resolution biomass map, Landsat-based tree cover datasets as well as local EFs in China. The results showed that the average annual Hg emission from open biomass burning in China amounted to 172.6 kg during 2000-2019, with a range of 63-398.5 kg. The largest Hg emissions were found in cropland (72%), followed by forest (25.9%), and grassland (2.1%). On a regional level, Northeast China (NE) and Southwest China (SW) were the two main contributors, together accounting for more than 60% of total Hg emissions. The temporal distribution of Hg emissions showed that the peaks occurred in 2003 and 2014. This is a comprehensive estimation of Hg emissions from open biomass burning in China by integrating various high-resolution remotely sensed data and nationwide localized EFs, which has important implications for understanding the role of open biomass burning in China in regional and global atmospheric Hg budget.

County-level and monthly resolution multi-pollutant emission inventory for residential solid fuel burning in Fenwei Plain, China

The Fenwei Plain (FWP) in central China is the fourth largest plain nationwide. This region has experienced severe air pollution during the past decades, largely due to residential solid fuel burning. A regional-scale emission inventory covering multi-pollutants was currently unavailable for this area due to the lack of localized emission factors (EFs) from various sources. In this study, localized EFs derived from previous in situ measurements and detailed county-level activity data were used to develop an emission inventory of particulate and gaseous pollutants for the source sector of five residential solid fuels in the FWP in 2020. Emissions of particulate matter with an aerodynamic diameter of ≤2.5 μm (PM_2.5), organic carbon (OC), elemental carbon (EC), ions, polycyclic aromatic hydrocarbons (PAHs), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) were estimated to be 230-290, 89-160, 20-29, 31-54, 0.93-22, 2100-3600, 64-87, 9.3-12, and 45-92 Gg/yr, respectively. The county-level distribution characteristics differed between pollutant species due to their different EFs and consumption patterns of solid fuels. Shouyang County emitted most for all pollutants (2.66%-4.91% of the region total) except PM_2.5 and SO₂, for which Xiangfen and Hongtong County emitted the most (2.64% and 2.90%), respectively. Emissions were higher in cold (SO₂ during November to January, other pollutants during November to February) than warm months. Uncertainties in this newly developed emission inventory were estimated to be 25.2%-69.8%, much lower than those of existing ones, demonstrating the reliability of this inventory. Gini coefficients indicated that EC, PAHs, NOx, and VOC emissions exhibited evident regional disparities, e.g., Yuncheng and Jinzhong had high pollution levels despite low economic output. Future emission control policies should first focus on developing regions with high pollution in FWP.

A synthesis of mercury research in the Southern Hemisphere, part 2: Anthropogenic perturbations

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

Emissions of Toxic Substances from Biomass Burning: A Review of Methods and Technical Influencing Factors

In the perspective of energy sustainability, biomass is the widely used renewable domestic energy with low cost and easy availability. Increasing studies have reported the health impacts of toxic substances from biomass burning emissions. To make proper use of biomass as residential solid energy, the evaluation of its health risks and environmental impacts is of necessity. Empirical studies on the characteristics of toxic emissions from biomass burning would provide scientific data and drive the development of advanced technologies. This review focuses on the emission of four toxic substances, including heavy metals, polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), and volatile organic compounds (VOCs) emitted from biomass burning, which have received increasing attention in recent studies worldwide. We focus on the developments in empirical studies, methods of measurements, and technical factors. The influences of key technical factors on biomass burning emissions are combustion technology and the type of biomass. The methods of sampling and testing are summarized and associated with various corresponding parameters, as there are no standard sampling methods for the biomass burning sector. Integration of the findings from previous studies indicated that modern combustion technologies result in a 2–4 times reduction, compared with traditional stoves. Types of biomass burning are dominant contributors to certain toxic substances, which may help with the invention or implementation of targeted control technologies. The implications of previous studies would provide scientific evidence to push the improvements of control technologies and establish appropriate strategies to improve the prevention of health hazards.

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

Formaldehyde (HCHO) plays a vital role in atmospheric chemistry and O₃ formation. Open biomass burning (OBB) is considered to be an important source of HCHO; however, its quantitative contribution to ambient HCHO remains poorly understood due to the lack of reliable high-resolution emission inventories. In this study, a satellite-based method coupled with local emission factors was developed to estimate the hourly primary emissions of HCHO and volatile organic compound (VOC) precursors from OBB in Guangdong (GD) Province of southern China. Furthermore, the contribution of OBB to ambient HCHO was quantified using the Community Multi-scale Air Quality model. The results suggested that in average OBB emissions contributed 5293 tons of primary HCHO per year, accounting for ~14% of the total anthropogenic HCHO emissions in GD. The ambient HCHO concentration ranged from 0.3 ppbv to 8.7 ppbv during normal days, and from 8 ppbv to 45 ppbv in downwind area during OBB impacted days. The monthly contribution of OBB to local HCHO levels reached up to 50% at locations with frequent fires and over 70% during a forest fire event. Ambient HCHO was heavily affected by primary OBB emissions near the source region and by the oxidation of OBB-emitted VOCs in the downwind area. Secondary HCHO formation from OBB emissions was enhanced during photochemical pollution episodes, especially under conditions of high O₃ and low NO_x. OBB-emitted ethene was identified as the most important VOC precursor of HCHO and contributed to the formation of ~50% of the secondary HCHO. The HCHO formation potential of cropland fires was 26% higher than that of forest fires. Our results suggest that OBB can elevate ambient HCHO levels significantly. Thus, strict control policies on OBB should be implemented, especially for open burning agricultural residues in upwind areas on serious photochemical pollution days.

Atmospheric Modelling of Mercury in the Southern Hemisphere and Future Research Needs: A Review

Mercury is a toxic pollutant that can negatively impact the population’s health and the environment. The research on atmospheric mercury is of critical concern because of the diverse process that this pollutant suffers in the atmosphere as well as its deposition capacity, which can provoke diverse health issues. The Minamata Convention encourages the protection of the adverse effects of mercury, where research is a part of the strategies and atmospheric modelling plays a critical role in achieving the proposed aim. This paper reviews the study of modelling atmospheric mercury based on the southern hemisphere (SH). The article discusses diverse aspects focused on the SH such as the spatial distribution of mercury, its emissions projections, interhemispheric transport, and deposition. There has been a discrepancy between the observed and the simulated values, especially concerning the seasonality of gaseous elemental mercury and total gaseous mercury. Further, there is a lack of research about the emissions projections in the SH and mercury deposition, which generates uncertainty regarding future global scenarios. More studies on atmospheric mercury behaviour are imperative to better understand the SH’s mercury cycle.

Temporal variation and potential origins of atmospheric speciated mercury at a remote island in South China Sea based on two-year field measurement data

This study explored the temporal variation, gas-particle partition, and potential origins of atmospheric speciated mercury at a remote island in the South China Sea. Two-year data of three mercury species was measured at the Taiping Island. Air masses were clustered into five transport routes (A-E) to resolve the potential origins of atmospheric mercury. Field measurement showed that the concentration of gaseous elemental mercury (GEM) (1.33 ± 0.52 ng/m³) was close to the GEM background level of Northern Hemisphere, while those of GOM and PHg were 13.39 ± 3.58 and 94.33 ± 30.25 pg/m³, respectively. Both regular and intensive samplings concluded a consistent trend of higher mercury level in winter and spring than that in summer and fall. GEM dominated atmospheric mercury in all seasons (86.2–98.5%), while the highest partition of particle-bound mercury (PHg) was observed in winter (13.8%). The highest GEM concentrations were observed for Route A originating from central China and western Taiwan Island, and followed by Routes D and E from the Philippines, Malaysia, and Indonesia, while the lowest concentrations of GEM were observed for Routes B and C originating from North China, Korea, and Japan. Most importantly, high correlation of GEM versus levoglucosan and K⁺ in PM_2.5 (r = 0.764 and 0.758, p < 0.01) confirmed that GEM was mainly emitted from biomass burning sources at the surrounding countries.

The moving of high emission for biomass burning in China: View from multi-year emission estimation and human-driven forces

Biomass burning (BB) has significant impacts on air quality, climate and human health. In China, the BB emission has changed substantially over the past decades while the multi-year variation held high uncertainty and the driving forces have addressed little attention. Here, this research aimed to conduct a comprehensive and systematic analysis of BB variation in China and provided precise and targeted BB emission reduction suggestions. The moving of high emission for BB from 2003 to 2014 was clearly identified, by the view of reliable emission estimation and anthropogenic impacts. Multiple satellite products, field survey, time varying biomass loading data and measured emission factors were adopted to better estimating BB emission and reducing the uncertainty. Social-economic analysis was added to assess the anthropogenic impacts on high emission variation quantitatively. Results showed that the cumulative BB emissions of OC, EC, CH₄, NO_X, NMVOC, SO₂, NH₃, CO, CO₂, PM_2.5 and PM₁₀ during 2003-2014 were 1.6 × 10⁴, 5.64 × 10³, 3.57 × 10⁴, 1.7 × 10⁴, 5.44 × 10⁴, 2.96 × 10³, 6.77 × 10³, 6.5 × 10⁵, 1.15 × 10⁷, 5.26 × 10⁴ and 6.04 × 10⁴ Gg, respectively. Crop straw burning (in-field and domestic) in northeast China plain (NEP), north China plain (NCP), northern arid and semiarid region and loess plateau were the key sources, averagely contributed 73% for all the pollutants emission. While domestic straw burning and firewood burning in Sichuan basin (SB), Yunnan-Guizhou plateau and southern China were main contributors, averagely accounting for 70% of all the pollutants emission. On regional level, high emissions were mainly found in SB, NCP and NEP. Temporally, high emissions were mainly found in crop sowing harvesting and heating seasons. From 2003 to 2014, the BB emission for different biomass species has changed significantly in different regions. High emission has gradually moved from SB to NCP and NEP. Firewood burning and domestic straw burning emission decreased by 47% and 14% in SB, respectively. In-field straw burning emission increased by 52% and 231% in NCP and NEP respectively and domestic straw burning emission increased by 62% in NEP. Emissions from heating season have decreased while emissions in corn harvest season were continuously increased. Analysis of Environmental kuznets curve, agricultural productivity level, human burning habits, rural energy structure and local control policies revealed the internal human driving strength of the variation for BB emission. The unbalanced development of social economy and the policy bias were primary drivers of limiting the BB management. BB emission will alleviate in NCP and aggravate in NEP. For the further emission reduction, effective measures for corn sources management, straw returning and rural energy utilization should be systematically considered. This research provides a clear evidence for the multi-year variation pattern of BB emissions, which is critical for pollution prediction, air quality modeling and targeted mitigation strategies for the key regions of China.

Energy-induced mercury emissions in global supply chain networks: Structural characteristics and policy implications

Mercury emission flows in the global supply chains have evolved into an ever-increasing complex network. However, the underlying structural features remain unknown. Therefore, the global embodied mercury flow network was constructed to reveal the characteristics of energy-induced mercury emissions embodied in international trade at both national and sectoral scales. The small-world nature of the global mercury flows network was identified at both scales. Results showed that the global mercury flow network can be divided into 4 national communities, within which the spillover effects of the interventions in one region spread more easily. Detecting the mercury-intensive supply-chain clusters highlights the importance of monitoring these clusters that dominate mercury emissions in global supply chains, which could offer insights on where policy can be implemented effectively. Moreover, vital regions (e.g., mainland China, the USA, and Germany) and sectors (e.g., Petroleum, Chemical and Non-Metallic Mineral Products, Metal Products and Electrical and Machinery in mainland China) for global mercury control have been unveiled by using an integrated centrality measurement system. Our results highlight that, for the overall mercury reduction, regional and even global collaboration should be enhanced along with efforts in individual regions, and enterprises in these important sectors should invest more to green their cluster-wise supply chains.