Black Carbon - A Silent Contributor to Climate Change

Black carbon is a potent climate-warming component of particulate matter formed by the incomplete combustion of fossil-fuels, wood and other fuels. Complete combustion would turn all the carbon in the fuel into carbon dioxide, but combustion is never complete, and CO2, CO, volatile organic compounds, organic compounds, and black carbon particles are formed in the process. It contributes to warming by converting incoming solar radiation to heat. When deposited on ice and snow, BC and co-emitted particles reduce surface albedo thereby melting the glaciers. The complex mixture of particulate matter resulting from incomplete combustion is referred as soot. When suspended in the atmosphere, black carbon contributes to warming by converting incoming solar radiations to heat. It also influences cloud formation and impacts regional circulation and rainfall pattern. The Artic and the glaciated regions such as Himalayas are particularly vulnerable to melting as a result. The present paper aims to review the work done on black carbon and its mitigation measure.

Characterization of Black Carbon and Its Correlations with VOCs in the Northern Region of Hangzhou Bay in Shanghai, China

Ozone and PM2.5 (all particulate matter with diameter of 2.5 µm or smaller) are currently two disturbing environmental issues in most cities of China. Black carbon (BC), mainly from incomplete combustion, is one of the most important components of PM2.5 because it can absorb light and contribute to haze pollution and global warming. Meanwhile, volatile organic compounds (VOCs) have become a major air pollutant due to their association with haze, ozone (O3), global warming and human health by direct or indirect processes. In this study, one year-long observation campaign of BC, VOCs and other conventional air pollutants was conducted in the Northern Region of the Hangzhou Bay (NRHB) in Shanghai, China. The results indicated that higher concentration of BC mainly occurred in the autumn and winter, especially in December. In December, higher BC concentrations were found when the air mass came from northwest where there is an important local freeway, or southwest where some adjacent southwest chemical industrial parks are located. Different from the characteristics of BC in urban areas reported by previous studies, the diurnal variation of BC exhibited three peaks, two of which coincided with the morning and evening rush hours which are related to the heavy diesel traffic from a nearby freeway, and the third peak was often found late at night, around 2 am, which might be associated with abnormal emissions from an industrial park or marine traffic in the ocean waterway. BC had weakly negative correlation with O3 and NO, and a strongly positive correlation with PM2.5, SO2, NO2 and NOx, which implies that some incomplete combustion sources might occur in the nearby regions. With regard to VOCs, BC had a strong positive correlation with alkane, alkenes, alkynes, aromatic and non-sulfur VOCs, particularly with aromatic organic matter. Unlike the stronger correlation with aromatics in the morning rush hours, a stronger correlation between BC and alkenes and alkynes during the evening rush hour was observed. The relationships between BC and VOCs, particularly with some specific VOCs species related to the neighboring chemical industrial park, demonstrated that the contribution of the surrounding chemical industrial parks to BC should not be neglected.

Combination of Primary Measures on Flue Gas Emissions in Grate-Firing Biofuel Boiler

Increasingly stringent limits for NOx and SO2 emission are forcing the investigation of new reduction methods. This study was conducted to determine the combination of primary measures, i.e., flue gas recirculation (FGR) and excess air effects on sulfur, nitrogen and hydrocarbon emissions, in boiler flue gas. Experimental research was performed using an experimental, small-scale (20 kW) model of an industrial biofuel boiler. During combustion of sunflower seed hulls at different FGR ratios and incomplete combustion regimes, the composition of flue gas (NO, NO2, N2O, HCN, NH3, SO2, SO3, H2S, CO, and CxHy) was compared, allowing an explanation of the determinants of emission concentration changes to be provided. Increasing the flue gas recirculation ratio in the primary air had a positive effect on reducing NOX and CO with certain organic compounds. However, an opposite effect on SO2 was observed. NOX and SO2 concentrations were found to be approximately 500 mg/m3 and 150 mg/m3 under a regular combustion regime. When the FGR ratio of 50% NOX concentration decreased by 110 mg/m3, the SO2 concentration increased by 60 mg/m3. The incomplete combustion regime reduced NOX concentration by 70 mg/m3, whereas SO2 concentration increased by 100 mg/m3. The influence of primary measures presented an unclear relationship to hydrocarbon emissions, with concentrations not exceeding 18 mg/m3.

Health Effect of Biomass Fuel Smoke

Almost half of the world population rely on solid (biomass fuel and coal) for cooking, heating and lightning purpose. The resultant exposure to fine particulate matter from household air pollution is the seventh-largest risk factor for global burden of disease causing between 2.6 and 3.8 million premature deaths per year. The health effect ranges from cardiovascular, respiratory, neurocognitive and reproductive health effect. The most important are cardiovascular and respiratory health effects; others are the risk of burns and cataract in the eyes. Biomass fuel is any living or recently living plant and animal-based material that is burned by humans as fuels, for example, wood, dried animal dung, charcoal, grass and other agricultural residues. Biomass fuels are at the low end of the energy ladder in terms of combustion efficiency and cleanliness. Incomplete combustion of biomass contributes majorly to household air pollution and ambient air pollution. A large number of health-damaging air pollutants are produced during the incomplete combustion of biomass. These include respirable particulate matter, carbon monoxide, nitrogen oxides, formaldehyde, benzene, 1, 3 butadiene, polycyclic aromatic hydrocarbons (PAHs), and many other toxic organic compounds. In this article, health effects of biomass fuel use will be described in details highlighting the most affected systems and organs of the body.

Methodology for the numerical solution of problems in relation to the coil-type electric heat exchangers for heating fuel

The specificity of the operating conditions of agricultural tractors in the agro-industrial complex requires the provision of reliable engine start at low ambient temperatures. Improving the starting qualities of a diesel engine and reducing incomplete combustion in the post-start period can be achieved by increasing the exergy of the air charge at the end of the compression stroke or increas-ing the exergy of the fuel injected into the combustion chamber. The purpose of the study is to re-duce the expenditure of exergy for prestarting a diesel engine, improve starting qualities and reduce incomplete combustion in the post-start period. To achieve this goal, the design of an electric heat exchanger was developed in the form of a coil from a high-pressure fuel line, into which a heating element is inserted. A method for calculating its main parameters was developed. Calculations showed that in order to ensure reliable start-up of a diesel engine in winter, it is necessary to heat the fuel in the nozzle to a temperature of 240 ° C in the thermal boost mode. A heater of about 98 Watts is required to reach this temperature within 270 seconds of priming. However, in order to maintain such a fuel temperature during the start-up process, it is necessary to make changes in the nozzle design in order to minimize heat losses into the walls of the fuel channel by applying a heat-insulating coating. With further engine operation in the post-start heating mode, the fuel temperature in the injector is reduced to 85-95 ° C.

Effect of Excess Air Levels on PAHs Content in Smoke During Charcoal Combustion in Grilling Process

Charcoal grilling may lead to carcinogenic PAHs contamination of grilled food from incomplete combustion of charcoal. The objective of this study was to determine the effect of complete combustion of charcoal on PAHs content in smoke during the grilling process. Firstly, proximate and ultimate compositions of the charcoal were determined to identify the amount of air required for combustion according to stoichiometry. Different excess air levels consisting of stoichiometric air, 60, 100 and 150% excess air during combustion of charcoal on 16 PAHs released in smoke were studied. Moreover, CO and CO2 concentrations were measured. The use of excess air decreased the emission factor of CO and increased the emission factor of CO2. The 16 PAHs contents in smoke produced from charcoal combusted with stoichiometric air, 60, 100 and 150% excess air were 73.62, 51.78, 27.68 and 19.23 μg/kg dry charcoal, respectively. The use of excess air during charcoal combustion resulted in significantly lower PAHs contents in the smoke. Therefore, the use of excess air during charcoal grilling is one way to reduce the risk of PAHs contamination in grilled food.