Emission factors, ozone and secondary organic aerosol formation potential of volatile organic compounds emitted from industrial biomass boilers

To evaluate the potential benefits of biomass use for air pollution control, this paper identified and quantified the emissions of major reactive organic compounds anticipated from biomass-fired industrial boilers. Wood pellets(WP) and straw pellets(SP) were burned to determine the volatile organic compound emission profiles for each biomass-boiler combination. More than 100 types of volatile organic compounds(VOCs) were measured from the two biomass boilers. The measured VOC species included alkanes, alkenes and acetylenes, aromatics, halocarbons and carbonyls. A single coal-fired boiler(CB) was also studied to provide a basis for comparison. Biomass boiler 1(BB1) emitted relatively high proportions of alkanes(28.9%–38.1% by mass) and alkenes and acetylenes(23.4%–40.8%),while biomass boiler 2(BB2) emitted relatively high proportions of aromatics(27.9%–29.2%)and oxygenated VOCs(33.0%–44.8%). The total VOC(TVOC) emission factors from BB1(128.59–146.16 mg/kg) were higher than those from BB2(41.26–85.29 mg/kg). The total ozone formation potential(OFP) ranged from 6.26 to 81.75 mg/m^3 with an average of 33.66 mg/m^3 for the two biomass boilers. The total secondary organic aerosol potential(SOAP) ranged from 61.56 to 211.67 mg/m^3 with an average of 142.27 mg/m^3 for the two biomass boilers.The emission factors(EFs) of TVOCs from biomass boilers in this study were similar to those for industrial coal-fired boilers with the same thermal power. These data can supplement existing VOC emission factors for biomass combustion and thus enrich the VOC emission inventory.

Chemical characteristics of road dust PM2.5 fraction in oasis cities at the margin of Tarim Basin

In order to understand the compositions characteristics of particulate matter with aerodynamic diameter less than 2.5μm(PM2.5)fraction in road dust(RD2.5)of oasis cities on the edge of Tarim Basin,30 road dust(RD)samples were collected in Kashi,Cele,and Yutian in the spring,2018,and RD2.5 was collected using the resuspension approach.Eight watersoluble ions,39 trace elements and 8 fractions of carbon-containing species in PM2.5 were analyzed.Ca2+and Ca were the most abundant ions and elements in RD2.5(7.1%and 9.5%).Cl-in RD2.5 was affected not only by attributed to saline-alkali soils in oasis cities of the Tarim Basin and dust from Taklimakan Desert but also by human activities.Moreover,the organic carbon/elemental carbon(OC/EC)ratio indicated that carbon components in RD2.5in Cele town mainly come from fossil fuel combustion,while those in Yutian and Kashi mainly come from biomass combustion.It is noteworthy that high Ca in RD2.5 was seriously affected by anthropogenic emissions,and high Na and K contents in RD2.5 could be derived from soil and desert dust.It was estimated that Cd,Tl,Sn and Cr were emitted from anthropogenic emissions using the enrichment factor.The coefficients of divergence(cOD)result indicated that the influence of local emission on road dust emission is greater than that of long-distance transmission.This study is the first time to comprehensively analyze the chemical characteristics of road dust in oasis cities,and the results provides the sources of road dust at the margin of Tarim Basin.

Smog chamber study on the evolution of fume from residential coal combustion

Domestic coal stoves are widely used in countryside and greenbelt residents in China for heating and cooking,and emit considerable pollutants to the atmosphere because of no treatment of their exhaust,which can result in deteriorating local air quality.In this study,a dynamic smog chamber was used to investigate the real-time emissions of gaseous and particulate pollutants during the combustion process and a static smog chamber was used to investigate the fume evolution under simulate light irradiation.The real-time emissions revealed that the total hydrocarbon （THC） and CO increased sharply after ignition,and then quickly decreased,indicating volatilization of hydrocarbons with low molecular weight and incomplete combustion at the beginning stage of combustion made great contribution to these pollutants.There was evident shoulder peak around 10min combustion for both THC and CO,revealing the emissions from vitrinite combustion.Additionally,another broad emission peak of CO after 30min was also observed,which was ascribed to the incomplete combustion of the inertinite.Compared with THC and CO,there was only one emission peak for NOx,SO 2 and particular matters at the beginning stage of combustion.The fume evolution with static chamber simulation indicated that evident consumption of SO 2 and NOx as well as new particle formation were observed.The consumption rates for SO 2 and NOx were about 3.44% hr-1 and 3.68% hr-1,the new particle formation of nuclei particles grew at a rate of 16.03 nm/hr during the first reaction hour,and the increase of the diameter of accumulation mode particles was evident.The addition of isoprene to the diluted mixture of the fume could promote O 3 and secondary particle formation.

Vertical distribution of volatile organic compounds conducted by tethered balloon in the Beijing-Tianjin-Hebei region of China

Volatile organic compounds(VOCs) as precursors of ozone and secondary organic aerosols can cause adverse effects on the environment and human health.However,knowledge of the VOC vertical profile in the lower troposphere of major Chinese cities is poorly understood.In this study,tethered balloon flights were conducted over the juncture of BeijingTianjin-Hebei in China during the winter of 2016.Thirty-six vertical air samples were collected on selected heavy and light pollution days at altitudes of 50-1000 meters above ground level.On average,the concentration of total VOCs(TVOCs) at 50-100 m was 4.9 times higher than at 900-1000 m(46.9 ppbV vs.8.0 ppbV).TVOC concentrations changed rapidly from altitudes of 50-100 to 401-500 m,with an average decrease of 72%.With further altitude increase,the TVOC concentration gradually decreased.The xylene/benzene ratios of 34/36 air samples were lower than 1.1,and the benzene/toluene ratios of 34/36 samples were higher than 0.4,indicating the occurrence of aged air mass during the sampling period.Alkenes contributed most in terms of both OH loss rate(39%-71%) and ozone formation potential(40%-72%),followed by aromatics(6%-38%).Finally,the main factors affecting the vertical distributions of VOCs were local source emission and negative dispersion conditions on polluted days.These data could advance our scientific understanding of VOC vertical distribution.

Characterization of coal burning-derived individual particles emitted from an experimental domestic stove

Coal combustion in the domestic stoves, which is common in most parts of the Chinese countryside, can release harmful substances into the air and cause health issues. In this study, particles emitted from laboratory stove combustion of the raw powder coals were analyzed for morphologies and chemical compositions by using transmission electron microscopy （TEM） coupled with energy-dispersive X-ray spectrometry （EDX）. The coal burning-derived individual particles were classified into two groups： carbonaceous particles （including soot aggregates and organic particles） and non-carbonaceous particles （including sulfate, mineral and metal particles）. The non-carbonaceous particles, which constituted a majority of the coal burning-derived emissions, were subdivided into Si-rich, S-rich, K-rich, Ca-rich, and Fe-rich particles according to the elemental compositions. The Si-rich, S-rich and K-rich particles are commonly observed in the coal burning emission. The proportions for particles of different types exhibit obvious coal-issue dependence. Burning of coal with high ash yield could emit more non-carbonaceous particles, and burning of coal with high sulfur content can emit more S-rich particles. By comparing the S-rich particles from this coal burning experiment with those in the atmosphere, we draw a conclusion that some S-rich particles in the atmosphere in China could be mainly sourced from coal combustion.

Emission factors of polycyclic aromatic hydrocarbons from domestic coal combustion in China

Domestic coal stove is widely used in China, especially for countryside during heating period of winter, and polycyclic aromatic hydrocarbons （PAHs） are important in flue gas of the stove. By using dilution tunnel system, samples of both gaseous and particulate phases from domestic coal combustion were collected and 18 PAH species were analyzed by GC-MS. The average emission factors of total 18 PAH species was 171.73 mg/kg, ranging from 140.75 to 229.11 mg/kg for bituminous coals, while was 93.98 mg/kg, ranging from 58.48 to 129.47 mg/kg for anthracite coals. PAHs in gaseous phases occupied 95% of the total of PAHs emission of coal combustion. In particulate phase, 3-ring and 4- ring PAHs were the main components, accounting for 80% of the total particulate PAHs. The total toxicity potency evaluated by benzo[a]pyrene-equivalent carcinogenic power, sum of 7 carcinogenic PAH components and 2,3,7,8-tetrachlorodibenzodioxin had a similar tendency. And as a result, the toxic potential of bituminous coal was higher than that of anthracite coal. Efficient emission control should be conducted to reduce PAH emissions in order to protect ecosystem and human health.

Characteristics of particulate-bound polycyclic aromatic hydrocarbons emitted from industrial grade biomass boilers

Polycyclic aromatic hydrocarbons（PAHs） are carcinogenic or mutagenic and are important toxic pollutants in the flue gas of boilers. Two industrial grade biomass boilers were selected to investigate the characteristics of particulate-bound PAHs： one biomass boiler retro-fitted from an oil boiler（BB1） and one specially designed（BB2） biomass boiler. One coal-fired boiler was also selected for comparison. By using a dilution tunnel system, particulate samples from boilers were collected and 10 PAH species were analyzed by gas chromatography–mass spectrometry（GC–MS）. The total emission factors（EFs） of PAHs ranged from 0.0064 to0.0380 mg/kg, with an average of 0.0225 mg/kg, for the biomass boiler emission samples. The total PAH EFs for the tested coal-fired boiler were 1.8 times lower than the average value of the biomass boilers. The PAH diagnostic ratios for wood pellets and straw pellets were similar.The ratio of indeno（1,2,3-cd）pyrene/[indeno（1,2,3-cd）pyrene ＋ benzo（g,h,i）perylene] for the two biomass boilers was lower than those of the reference data for other burning devices, which can probably be used as an indicator to distinguish the emission of biomass boilers from that of industrial coal-fired boilers and residential stoves. The toxic potential of the emission from wood pellet burning was higher than that from straw pellet burning, however both of them were much lower than residential stove exhausts.

Characterization of a new smog chamber for evaluating SAPRC gas-phase chemical mechanism

A new state-of-the-art indoor smog chamber facility(CAPS-ZJU) has been constructed and characterized at Zhejiang University,which is designed for chemical mechanism evaluation under well-controlled conditions.A series of characterization experiments were performed to validate the well-established experimental protocols,including temperature variation pattern,light spectrum and equivalent intensity(JNO2),injection and mixing performance,as well as gases and particle wall loss.In addition,based on some characterization experiments,the auxiliary wall mechanism has been setup and examined.Fifty chamber experiments were performed across a broad range of experimental scenarios,and we demonstrated the ability to utilize these chamber data for evaluating SAPRC chemical mechanism.It was found that the SAPRC-11 can well predict the 03 formation and NO oxidation for almost all propene runs,with 6 hr △(O3-NO) model error of-3%±7%,while the final O3 was underestimated by-20% for isoprene experiments.As for toluene and p-xylene experiments,it was confirmed that SAPRC-11 has significant improvement on aromatic chemistry than earlier version of SAPRC-07,although the aromatic decay rate was still underestimated to some extent.The model sensitivity test has been carried out,and the most sensitive parameters identified are the initial concentrations of reactants and the light intensity as well as HONO offgasing rate and 03 wall loss rate.All of which demonstrated that CAPS-ZJU smog chamber could derive high quality experimental data,and could provide insights on chamber studies and chemical mechanism development.