Primary PM2.5 and trace gas emissions from residential coal combustion: assessing semi-coke briquette for emission reduction in the Beijing-Tianjin-Hebei region, China

In response to severe haze pollution, the Chinese State Council set PM2.5 improvement targets for the Beijing-Tianjin-Hebei (BTH) region in 2013. To achieve the targets for the residential sector, semi-coke briquettes are being considered as a replacement for traditional raw coals with the help of financial subsidy, but information on the emission from them and the impacts on the air quality is limited. Laboratory experiments were conducted to determine emission factors (EFs) for a typical semi-coke briquette, its parent material (bituminous raw-coal-chunk) and three types of traditional coals (bituminous raw-coal-chunk, anthracite raw-coal-chunk and anthracite coal-briquette) extensively used in BTH. Compared with the parent material, significant lower EFs of primary PM2.5, organic carbon (OC), element carbon (EC), the sum of 16 polycyclic aromatic hydrocarbon components (PAHs), SO42−, NO3−, hazardous trace elements (HTEs) and NOx were found in semi-coke briquette. A scenario for the BTH region in 2015 in which raw coals were replaced with the semi-coke briquette showed that amounts of pollutants emitted from residential coal combustion could decrease by 91.6% for primary PM2.5, 94.0% for OC, 99.6% for EC, 99.9% for PAHs, 94.2% for NO3−, 45.6% for HTEs, 70.9% for NOx and 22.3% for SO2. However, SO42− loadings evidently would increase if raw coals were replaced with either semi-coke briquette or anthracite coal-briquette. Geographic distributions of modeled reductions were developed to identify emission-reducing hot-spots and aid in the development of clean energy policies. Replacement of traditional raw coals with the semi-coke briquette apparently could lead to significant environmental improvements in BTH and other regions in China

Spatial distributions and sequestrations of organic carbon and black carbon in soils from the Chinese loess plateau

Concentrations of soil organic carbon (SOC), black carbon (BC), char, and soot in topsoils (0-20 cm) and vertical soil profiles (0-100 cm) from the Chinese Loess Plateau (CLP) were investigated. Objectives of the study were to establish the spatial distributions and estimate the sequestrations of these substances. The SOC, BC, char and soot concentrations were higher in the eastern and southeastern parts of the plateau and lower in the north, which is consistent with the patterns of economic development and energy consumption. The highest average SOC concentration was found in the clayey loess zone, followed by the loess and sandy loess zones. Similar trends were observed for BC, char and soot, suggesting interactions with clay and silt are potentially important influences on DC and BC. The SOC contents in topsoils varied from 0.31 to 51.81 g kg(-1), with a mean value of 6.54 g kg(-1), while BC and char concentrations were 0.02 to 5.5 g kg(-1) and 0.003 to 4.19 g kg(-1), respectively, and soot ranged from 0.01 to 132 g kg(-1). Unlike SOC, both BC and char decreased with soil depth, whereas soot showed little variation with depth. BC and char were correlated in the topsoils, and both correlated moderately well with SOC (R-2=0.60) and soot (R-2= 0.53). The SOC pools sequestered in the 0 to 20 cm and 0 to 100 cm depths were estimated to be 0.741 and 3.63 Pg, respectively, and the BC pools sequestered in the 0 to 20 cm and 0 to 100 cm depths were 0.073 and 0.456 Pg, respectively. Therefore the quantity of carbon stored in the sediments of the CLP evidently exceeds 10(9) tons. The char contained in the upper 20 cm layer was 0.053 Pg, which amounted to 72.5% of the BC in that layer.</p

Characteristics and Sources of Black Carbon in Atmospheric Dustfall Particlesfrom Huangshi, China

Concentrations of carbonaceous particles in atmospheric dustfall particles in Huangshi, an industrial city in central China, were determined using a thermal-optical reflectance method. The black carbon (BC) contents in ninety-five dustfall samples ranged from 4.3 to 64.9 g kg⁻&sup1; with an average of 17.0 g kg⁻&sup1;. These values were higher than those in world background soils and demonstrated serious contamination of the environment in this city. Overall, BC accounted for 17.6-71.3% (mean: 42.0%) of the organic carbon (OC), and BC and OC were positively correlated (r&sup2; = 0.90). Average char and soot contents were 8.01 g kg-1 and 8.65 g kg⁻&sup1;, respectively, and char/soot ratios ranged from 0.28 to 1.97 with an average of 1.01. All the measured carbonaceous species positively correlated with each another, suggesting their common sources. BC, char, and soot showed large spatial distribution variability, with high levels of BC adjacent to the presumed emission sources, such as a power plant and railway line. Analyses of BC/OC and char/soot ratios indicate major impacts from fossil fuel combustion, especially motor vehicle emissions and coal combustion. Industrial dusts related to coal use appear to be the major contributor to BC in dustfall, and this is likely related to the extensive industrial activities in the city, including metal smelting.</p

Mixing State of Black Carbon Aerosol in a Heavily Polluted Urban Area of China: Implications for Light Absorption Enhancement

Black carbon (BC) is important for climate forcing, and its effects on the Earth&#39;s radiative balance remain a major uncertainty in climate models. In this study, we investigated the mixing state of refractory black carbon (rBC) and aerosol optical properties in a polluted atmosphere at Xi&#39;an, western China. The average rBC mass concentration was 9.9 mu g m (3) during polluted periods, 7.6 times higher than that in clean periods. About 48.6% of the rBC was internally-mixed or coated with nonrefractory materials during polluted periods; this was 27% higher than in clean periods. Correlation analysis between the number fraction of thickly-coated rBC particles (f(BC)) and the major particulate species indicate that organics may be the primary contributor to rBC coatings during polluted periods. The average mass absorption cross section of rBC (MAC(BC)) particles at lambda = 870 nm was 7.6 +/- 0.02 m(2) g(-1) for the entire campaign. The MAC(BC) showed a positive correlation with f(BC), and the enhancement of MAC(BC) due to internal mixing was 1.8 times. These observations suggest that an enhancement of BC absorption by a factor of similar to 2 could be appropriate for climate models associated with high PM2.5 levels.</p

High secondary aerosol contribution to particulate pollution during haze events in China

Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations(1). In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health(2,3). In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China(3,7,8). Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi&#39;an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China&#39;s PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.</p