The Emission Characteristics Of Residential Solid Fuel Combustion And Its Effects On Air Quality In Rural Regions Of China

Residential solid fuels combustion is the main source of air pollution in China.Therefore,obtaining the emission characteristics of individual particles from residential solid fuels combustion is helpful for source apportionment of aerosol particles and investigating the formation mechanism of air pollution in China.In this study,the primary particles from residential biomass,coal chunk,and honeycomb briquette combustion were collected in the laboratory simulation experiments or village field measurements,and their physicochemical properties were analyzed by individual particle analysis method and bulk sample analysis method.Then,we constructed the source profile database of individual particles from residential solid fuels combustion.Moreover,we also analyzed the physicochemical properties of aerosol particles collected from a village in North China during wintertime where the solid fuels were the dominant household fuels.Using the source profile database,we further analyzed the emission sources of aerosol particles in the village,and then investigated the effects of primary emission from residential solid fuels combustion on village air quality.The main conclusions of this study are listed as follows:The physicochemical properties of primary particles emitted from residential biomass combustion were obtained in this study.Our results reveal that the emission characteristics of different types of biomass fuels are quite different.Residential wood fuels combustion emits abundant carbonaceous particles,but few K-rich particles.On the contrary,residential crop straw fuels combustion could emit abundant K-rich particles.Moreover,we found that the emission characteristics of biomass combustion obtained from village field measurement and laboratory research are also different.Compared to the emissions from laboratory simulation experiments,there are more soot particles in the emissions from village field measurements in North China,but less soot particles in these emissions in Tibet Plateau.This result was related to the different combustion conditions.The emission characteristics of residential coal chunk combustion were obtained in this study.We investigated the characteristics of a complete combustion process of coal,and our results reveal that organic matters were the dominant component in emissions from the ignition stage.However,after the ignition stage,the proportion of organic matters gradually decreased,while the proportion of inorganic components gradually increased.Moreover,we found that the dilution process did not have a significant effect on the morphology and composition of the individual primary particles in the smoke.The results obtained from village field measurements and laboratory simulation experiments reveal that residential coal chunk combustion mainly emitted carbonaceous matters,including organic matters and soot particles.However,we found that the primary particles from coal-fired power plants were dominated by non-carbonaceous matters,such as mineral,which is obviously different from those of residential coal combustion.We found that the different combustion conditions are the key reasons why there are huge differences between individual particles emitted from coal-fired power plants and residential coal combustion.The emission characteristics of residential honeycomb briquette combustion were obtained in this study.Here,we first report an overlooked source of atmospheric nanosized Pb particles,finding that residential honeycomb briquette combustion emits large numbers of nanosized Pb-rich particles.33.7±19.9%of primary particles by number from residential honeycomb briquette combustion contain the crystalline Pb particles.These Pb-rich particles range in size from 14 to 956 nm with a mean diameter of 117 nm.Compared with raw coal chunks,honeycomb briquette combustion can efficiently reduce the emissions of carbonaceous particles,but largely increase nanosized Pb particle emissions.This result is attributed to two key factors:1)higher Pb content in honeycomb briquette（63.6μg/g）than that in coal chunk（8.5μg/g）,and2)higher Pb release rate for honeycomb briquette（62.3%）caused by honeycomb structure than that for coal chunk（20.1%）.In this study,we obtained the morphology,composition,mixing state,and size distribution of primary particles emitted from residential solid fuels combustion.This information constructs a source profile database of individual particles from residential solid fuels combustion.We also found the unique individual particles emitted from each solid fuel.For biomass,the unique particle is K-rich particles or spherical and dome-like organic particles containing K element;for coal chunk,it is spherical and dome-like organic particles containing S element but none K element;for honeycomb briquette,it is Pb-rich particles.These unique individual particles could help us trace the sources of atmospheric aerosol particles.The physicochemical properties of aerosol particles in the village in North China during wintertime were obtained in this study.Our results reveal that at the village site,each day was divided into four periods:cooking,daytime,heating,and midnight periods.The highest PM_2.5 concentration occurred during the cooking period（236±88μg/m³）,which was characterized by high concentrations of K⁺and abundant primary OM-K particles（i.e.,organic matter mixed with K-salts）.According to the source profile database of individual particles,we found that these K-containing particles were mainly from residential biomass combustion.The second highest PM_2.5 concentration was found during the heating period（161±97μg/m³）,and the PM_2.5 contained abundant spherical and dome-like primary OM particles with S element but none K element.According to the source profile database of individual particles,we found these organic particles was mainly from residential coal chunk combustion.These results reveal that residential solid fuels combustion led to a sharp increase in PM_2.5 concentrations and organic matter contents during the cooking and heating stages in the village.Our study indicates that the village atmosphere is more affected by direct emissions from residential solid fuels combustion than urban areas,which further results in the fact that village atmosphere contains more primary organic aerosols than urban areas.