Sihua Lu

Distributions and Source Apportionment of Ambient Volatile Organic Compounds in Beijing City, China

Abstract Ambient measurements of 108 volatile organic compounds (VOCs), including alkanes, alkenes, aromatics, and halogenated hydrocarbons, were conducted from 2002 to 2003 at six sites in Beijing city. The mean mass concentration of total VOCs was 132.6 ± 52.2 μg/m3, with alkanes, aromatics, and alkenes accounting for 35%, 22%, and 17%, respectively. The concentrations of most VOC species showed a seasonal pattern, with higher values in November, mildly lower in March, and much lower in July. In winter and spring, apparent diurnal variations of reactive compounds such as 1,3-butadiene and isoprene were observed, whereas those were not distinct in summer. The propylene equivalent concentration was used to evaluate the contribution of individual VOCs in ozone formation. Reactive olefins from anthropogenic emissions dominated the reactions with OH at each season. In summer, isoprene became the largest contributor, followed by 1-butene and propene. The source profiles in Beijing, including vehicle exhaust, gasoline vapor, painting operations, and asphalt pavement, were investigated. Based on the measurement of source profiles and ambient concentrations of VOCs in Beijing, chemical mass balance receptor model was applied to estimate contributions of several potential VOCs sources in Beijing. The results indicated that vehicle exhaust contributed on average 57.7%, followed by painting operations, gasoline vapor, and liquefied petroleum gas (LPG) at 12.4%, 11.3%, and 5.8%, respectively.

Effects of soil organic matter on the development of the microbial polycyclic aromatic hydrocarbons (PAHs) degradation potentials.

The microbial activity in soils was a critical factor governing the degradation of organic micro-pollutants. The present study was conducted to analyze the effects of soil organic matter on the development of degradation potentials for polycyclic aromatic hydrocarbons (PAHs). Most of the degradation kinetics for PAHs by the indigenous microorganisms developed in soils can be fitted with the Logistic growth models. The microbial activities were relatively lower in the soils with the lowest and highest organic matter content, which were likely due to the nutrition limit and PAH sequestration. The microbial activities developed in humic acid (HA) were much higher than those developed in humin, which was demonstrated to be able to sequester organic pollutants stronger. The results suggested that the nutrition support and sequestration were the two major mechanisms, that soil organic matter influenced the development of microbial PAHs degradation potentials.

Biomass burning contributions to ambient VOCs species at a receptor site in the Pearl River Delta (PRD), China.

Ambient VOCs were measured by a proton transfer reaction-mass spectrometer (PTR-MS) at a receptor site in the Pearl River Delta (PRD) during October 19-November 18, 2008. Biomass burning plumes are identified by using acetonitrile as tracer, and enhancement ratios (ERs) of nine VOCs species relative to acetonitrile are obtained from linear regression analysis and the source-tracer-ratio method. Enhancement ratios determined by the two different methods show good agreement for most VOCs species. Biomass burning contributions are investigated by using the source-tracer-ratio method. Biomass burning contributed 9.5%-17.7% to mixing ratios of the nine VOCs. The estimated biomass burning contributions are compared with local emission inventories. Large discrepancies are observed between our results and the estimates in two emission inventories. Though biomass burning emissions in TRACE-P inventory agree well with our results, the VOCs speciation for aromatic compounds may be not appropriate for Guangdong.

Process-specific emission characteristics of volatile organic compounds (VOCs) from petrochemical facilities in the Yangtze River Delta, China.

Process-specific emission characteristics of volatile organic compounds (VOCs) from petrochemical facilities were investigated in the Yangtze River Delta, China. Source samples were collected from various process units in the petrochemical, basic chemical, and chlorinated chemical plants, and were measured using gas chromatography-mass spectrometry/flame ionization detection. The results showed that propane (19.9%), propene (11.7%), ethane (9.5%) and i-butane (9.2%) were the most abundant species in the petrochemical plant, with propene at much higher levels than in petrochemical profiles measured in other regions. Styrene (15.3%), toluene (10.3%) and 1,3-butadiene (7.5%) were the major species in the basic chemical industry, while halocarbons, especially dichloromethane (15.2%) and chloromethane (7.5%), were substantial in the chlorinated chemical plant. Composite profiles were calculated using a weight-average approach based on the VOC emission strength of various process units. Emission profiles for an entire petrochemical-related industry were found to be process-oriented and should be established considering the differences in VOC emissions from various manufacturing facilities. The VOC source reactivity and carcinogenic risk potential of each process unit were also calculated in this study, suggesting that process operations mainly producing alkenes should be targeted for possible controls with respect to reducing the ozone formation potential, while process units emitting 1,3-butadiene should be under priority control in terms of toxicity. This provides a basis for further measurements of process-specific VOC emissions from the entire petrochemical industry. Meanwhile, more representative samples should be collected to reduce the large uncertainties.

Development and validation of a cryogen-free automatic gas chromatograph system (GC-MS/FID) for online measurements of volatile organic compounds

An automatic gas chromatograph system equipped with a mass spectrometer and a flame ionization detector (GC-MS/FID) was developed for online measurements of volatile organic compounds (VOCs) in the atmosphere. This system consisted of a custom-built cryogen-free cooling device that can create an ultra-low temperature of −165 °C, a two-channel sampling and pre-concentration system, and a commercial GC-MS/FID. One channel in the sampling and pre-concentration system was designated to trap C2–C5 hydrocarbons, whereas the other was designed to trap other VOC species. The newly developed GC-MS/FID system was then employed to measure VOCs in ambient air, and its observation data were compared with those from three well-established techniques, including an offline GC-MS/FID coupled with canister sampling, a proton transfer reaction-mass spectrometer (PTR-MS), and an online gas chromatograph system equipped with an FID and a photo ionization detector (GC-FID/PID). The online and offline GC-MS/FID measurements for alkanes, acetylene, C2–C3 alkenes, C6–C8 aromatics, and halocarbons showed good agreement. In addition, the online GC-MS/FID measurements for C6–C9 aromatics, acetone, and methacrolein + methylvinylketone (MACR + MVK) agreed well with the PTR-MS observations. Mixing ratios of C2–C7 alkanes, C3–C5 alkenes, and C6–C8 aromatics also showed good agreement between the online GC-MS/FID and GC-FID/PID techniques. These inter-comparison results demonstrated the accuracy of online GC-MS/FID measurements for C2–C12 NMHCs, C3–C4 carbonyls, and halocarbons.

Emission factors of gaseous carbonaceous species from residential combustion of coal and crop residue briquettes

Experiments were performed to measure the emission factors (EFs) of gaseous carbonaceous species, such as CO2, CO, CH4, and non-methane volatile organic compounds (NMVOCs), from the combustion of five types of coal of varying organic maturity and two types of biomass briquettes under residential burning conditions. Samples were collected in stainless steel canisters and 2,4-dinitrophenylhydrazine (DNPH) cartridges and were analyzed by GC-FID/MS and HPLC, respectively. The EFs from crop residue briquette burning were generally higher than those from coals, with the exception of CO2. The dominant NMVOC species identified in coal smoke were carbonyls (41.7%), followed by C2 unsaturated hydrocarbons (29.1%) and aromatics (12.1%), while C2 unsaturated hydrocarbons were the dominant species (68.9%) emitted from the combustion of crop residue briquettes, followed by aromatics (14.4%). A comparison of burning normal crop residues in stoves and the open field indicated that briquettes emitted a larger proportion of ethene and acetylene. Both combustion efficiency and coal organic maturity had a significant impact on NMVOC EFs from burning coal: NMVOC emissions increased with increasing coal organic maturity but decreased as the combustion efficiency improved. Emissions from the combustion of crop residue briquettes from stoves occurred mainly during the smoldering process, with low combustion efficiency. Therefore, an improved stove design to allow higher combustion efficiency would be beneficial for reducing emissions of carbonaceous air pollutants.

Carbonyl emissions from heavy-duty diesel vehicle exhaust in China and the contribution to ozone formation potential

Fifteen heavy-duty diesel vehicles were tested on chassis dynamometer by using typical heavy duty driving cycle and fuel economy cycle. The air from the exhaust was sampled by 2,4-dinitrophenyhydrazine cartridge and 23 carbonyl compounds were analyzed by high performance liquid chromatography. The average emission factor of carbonyls was 97.2 mg/km, higher than that of light-duty diesel vehicles and gasoline-powered vehicles. Formaldehyde, acetaldehyde, acetone and propionaldehyde were the species with the highest emission factors. Main influencing factors for carbonyl emissions were vehicle type, average speed and regulated emission standard, and the impact of vehicle loading was not evident in this study. National emission of carbonyls from diesel vehicles exhaust was calculated for China, 2011, based on both vehicle miles traveled and fuel consumption. Carbonyl emission of diesel vehicle was estimated to be 45.8 Gg, and was comparable to gasoline-powered vehicles (58.4 Gg). The emissions of formaldehyde, acetaldehyde and acetone were 12.6, 6.9, 3.8 Gg, respectively. The ozone formation potential of carbonyls from diesel vehicles exhaust was 537 mg O3/km, higher than 497 mg O3/km of none-methane hydrocarbons emitted from diesel vehicles.

The contributions of biomass burning to primary and secondary organics: A case study in Pearl River Delta (PRD), China.

Synchronized online measurements of gas- and particle- phase organics including non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs) and submicron organic matters (OM) were conducted in November 2010 at Heshan, Guangdong provincial supersite, China. Several biomass burning events were identified by using acetonitrile as a tracer, and enhancement ratios (EnRs) of organics to carbon monoxide (CO) obtained from this work generally agree with those from rice straw burning in previous studies. The influences of biomass burning on NMHCs, OVOCs and OM were explored by comparing biomass burning impacted plumes (BB plumes) and non-biomass burning plumes (non-BB plumes). A photochemical age-based parameterization method was used to characterize primary emission and chemical behavior of those three organic groups. The emission ratios (EmRs) of NMHCs, OVOCs and OM to CO increased by 27-71%, 34-55% and 67% in BB plumes, respectively, in comparison with non-BB plumes. The estimated formation rate of secondary organic aerosol (SOA) in BB plumes was found to be 24% faster than non-BB plumes. By applying the above emission ratios to the whole PRD, the annual emissions of VOCs and OM from open burning of crop residues would be 56.4 and 3.8Gg in 2010 in PRD, respectively.

Investigation of carbonyl compound sources at a rural site in the Yangtze River Delta region of China

Carbonyl compounds are important intermediates in atmospheric photochemistry, but their primary sources are still not understood well. In this work, carbonyls, hydrocarbons, and alkyl nitrates were continuously measured during November 2011 at a rural site in the Yangtze River Delta region of China. Mixing ratios of carbonyls and hydrocarbons showed large fluctuations during the entire measurement. The average level for total measured volatile organic compounds during the pollution episode from 25th to 27th November, 2011 was 91.6 ppb, about 7 times the value for the clean period of 7th-8th, November, 2011. To preliminarily identify toluene sources at this site, the emission ratio of toluene to benzene (T/B) during the pollution episode was determined based on photochemical ages derived from the relationship of alkyl nitrates to their parent alkanes. The calculated T/B was 5.8 ppb/ppb, significantly higher than the values of 0.2-1.7 ppb/ppb for vehicular exhaust and other combustion sources, indicating the dominant influence of industrial emissions on ambient toluene. The contributions of industrial sources to ambient carbonyls were then calculated using a multiple linear regression fit model that used toluene and alkyl nitrates as respective tracers for industrial emission and secondary production. During the pollution episode, 18.5%, 69.0%, and 52.9% of measured formaldehyde, acetaldehyde, and acetone were considered to be attributable to industrial emissions. The emission ratios relative to toluene for formaldehyde, acetaldehyde, and acetone were determined to be 0.10, 0.20 and 0.40 ppb/ppb, respectively. More research on industrial carbonyl emission characteristics is needed to understand carbonyl sources better.

Characterization of non-methane hydrocarbons and their sources in an industrialized coastal city, Yangtze River Delta, China

Ningbo is a highly industrialized city in the coastal area of the Yangtze River Delta (YRD), China. Large emissions and transport of non-methane hydrocarbons (NMHCs) may contribute to regional ozone (O3) and particulate matter (PM) pollution; however, the concentrations and sources of ambient NMHCs have not yet been investigated in Ningbo. In this study, ambient NMHCs were measured at two residential (SZ and CX) and two industrial (ZH and BL) sites and one suburban (XS) site over ten consecutive days in each season (10-20 December 2012 in winter, 14-23 April 2013 in spring, 15-24 July 2013 in summer, 22-31 October 2013, in autumn). A positive matrix factorization (PMF) model using multiple site data was deployed to explore the source contributions and their spatial and seasonal characteristics. The measurement results showed obvious seasonal variations in ambient NMHC concentrations (ranging from 17.89-28.48ppbv); chemical compositions were similar among the five sampling sites. PMF analysis showed that the petrochemical industry was the largest contributor (an average of 35.64%) to ambient NMHCs, while contributions of smaller sources (i.e., chemical and paint industries [14.34%], fuel and tank evaporation [16.02%], and residential solvent usage [7.24%]) showed spatial variations. Liquefied petroleum gas and fuel and tank evaporation contributed more in summer and autumn, while the contribution of the chemical and paint industries was greater in spring and winter. An evaluation of the ozone formation potential and secondary organic aerosol potential suggested that petrochemical and solvent-related sources were key parameters in mitigation of secondary pollutant formation. Seasonal variations in source contributions should be considered when formulating an effective NMHC abatement strategy.