Chemical Characteristics and Source-Specific Health Risks of the Volatile Organic Compounds in Urban Nanjing, China

This work comprehensively investigated the constituents, sources, and associated health risks of ambient volatile organic compounds (VOCs) sampled during the autumn of 2020 in urban Nanjing, a megacity in the densely populated Yangtze River Delta region in China. The total VOC (TVOC, sum of 108 species) concentration was determined to be 29.04 ± 14.89 ppb, and it was consisted of alkanes (36.9%), oxygenated VOCs (19.9%), halogens (19.1%), aromatics (9.9%), alkenes (8.9%), alkynes (4.9%), and others (0.4%). The mean TVOC/NO_x (ppbC/ppbv) ratio was only 3.32, indicating the ozone control is overall VOC-limited. In terms of the ozone formation potential (OFP), however, the largest contributor became aromatics (41.9%), followed by alkenes (27.6%), and alkanes (16.9%); aromatics were also the dominant species in secondary organic aerosol (SOA) formation, indicative of the critical importance of aromatics reduction to the coordinated control of ozone and fine particulate matter (PM_2.5). Mass ratios of ethylbenzene/xylene (E/X), isopentane/n--pentane (I/N), and toluene/benzene (T/B) ratios all pointed to the significant influence of traffic on VOCs. Positive matrix factorization (PMF) revealed five sources showing that traffic was the largest contributor (29.2%), particularly in the morning. A biogenic source, however, became the most important source in the afternoon (31.3%). The calculated noncarcinogenic risk (NCR) and lifetime carcinogenic risk (LCR) of the VOCs were low, but four species, acrolein, benzene, 1,2-dichloroethane, and 1,2-dibromoethane, were found to possess risks exceeding the thresholds. Furthermore, we conducted a multilinear regression to apportion the health risks to the PMF-resolved sources. Results show that the biogenic source instead of traffic became the most prominent contributor to the TVOC NCR and its contribution in the afternoon even outpaced the sum of all other sources. In summary, our analysis reveals the priority of controls of aromatics and traffic/industrial emissions to the efficient coreduction of O₃ and PM_2.5; our analysis also underscores that biogenic emissions should be paid special attention if considering the direct health risks of VOCs.

VOC Characteristics and Their Source Apportionment in the Yangtze River Delta Region during the G20 Summit

To evaluate the effectiveness of measures to reduce the levels of volatile organic compounds (VOCs), which are important precursors of ground-level ozone formation, the real-time monitoring data of VOCs at the urban Zhaohui supersite (ZH), the Dianshan Lake regional supersite (DSL) and the urban Yixing station (YX) in the Yangtze River Delta region were analyzed from 23 August to 15 September 2016 during the G20 Hangzhou Summit. The average mole ratios of VOCs at the three sites were 6.56, 21.33 and 19.62 ppb, respectively, which were lower than those (13.65, 27.72 and 21.38 ppb) after deregulation. The characteristics of the VOCs varied during the different control periods. Synoptic conditions and airmass transport played an important role in the transport and accumulation of VOCs and other pollutants, which affected the control effects. Using the positive matrix factorization (PMF) method in source apportionment, five factors were identified, namely, vehicle exhaust (19.66–31.47%), plants (5.59–17.07%), industrial emissions (13.14–33.82%), fuel vaporization (12.83–26.34%) and solvent usage (17.84–28.95%) for the ZH and YX sites. Factor 4 was identified as fuel vaporization + incomplete combustion (21.69–25.35%) at the DSL site. The Non-parametric Wind Regression (NWR) method showed that regional transport was the main factor influencing the VOC distribution.

A Spatial-Temporal Resolved Validation of Source Apportionment by Measurements of Ambient VOCs in Central China

Understanding the sources of volatile organic compounds (VOCs) is essential in the implementation of abatement measures of ground-level ozone and secondary organic aerosols. In this study, we conducted offline VOC measurements at residential, industrial, and background sites in Wuhan City from July 2016 to June 2017. Ambient samples were simultaneously collected at each site and were analyzed using a gas chromatography–mass spectrometry/flame ionization detection system. The highest mixing ratio of total VOCs was measured at the industrial site, followed by the residential, and background sites. Alkanes constituted the largest percentage (>35%) in the mixing ratios of quantified VOCs at the industrial and residential sites, followed by oxy-organics and alkenes (15–25%).The values of aromatics and halohydrocarbons were less than 15%. By contrast, the highest values of oxy-organics accounted for more than 30%. The model of positive matrix factorization was applied to identify the VOC sources and quantify the relative contributions of various sources. Gasoline-related emission (the combination of gasoline exhaust and gas vapor) was the most important VOC-source in the industrial and residential areas, with a relative contribution of 32.1% and 40.4%, respectively. Industrial process was the second most important source with a relative contribution ranging from 30.0% to 40.7%. The relative contribution of solvent usage was 6.5–22.3%. Meanwhile, the relative contribution of biogenic emission was only within the range of 2.0–5.0%. These findings implied the importance of controlling gasoline-related and industrial VOC emissions in reducing the VOC emissions in Wuhan.

Analysis of ambient formaldehyde in the eastern region of India along Indo-Gangetic Plain

Ambient levels of formaldehyde (HCHO) were measured in the tropical urban mega city of Kolkata from July 2012 to April 2014, based on USEPA Compendium Method TO-11A using 2,4-dinitrophenylhydrazine (2,4-DNPH). The samples were analyzed by isocratic reverse-phase high-performance liquid chromatography (HPLC) with an ultraviolet detector at a wavelength of 360 nm. High values of HCHO were recorded at our site. The highest and average HCHO mixing ratio measured for the entire study period was 803 and 217 ppbv respectively. Seasonal wind regimes have been found to influence the seasonal pattern of HCHO mixing ratio at this site resulting in relatively higher mixing ratio of HCHO during the pre-monsoon periods as compared to the others. Apart from these, sampling-based measurements of CH4 and continuous measurements of ozone (O3) and CO were also performed with the objective to study the interrelationship of HCHO with these species. The results suggest the presence of highly complex chemistry among them.

Photochemical modeling of the Ozark isoprene volcano: MEGAN, BEIS, and their impacts on air quality predictions

Biogenic volatile organic compounds (BVOCs) contribute substantially to atmospheric carbon, exerting influence on air quality and climate. Two widely used models, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Biogenic Emission Inventory System (BEIS) are employed to generate emissions for application in the CMAQ air quality model. Predictions of isoprene, monoterpenes, ozone, formaldehyde, and secondary organic carbon (SOC) are compared to surface and aloft measurements made during an intensive study in the Ozarks, a large isoprene emitting region. MEGAN and BEIS predict spatially similar emissions but magnitudes differ. The total VOC reactivity of the emissions, as developed for the CB05 gas-phase chemical mechanism, is a factor of 2 different between the models. Isoprene estimates by CMAQ-MEGAN are higher and more variable than surface and aloft measurements, whereas CMAQ-BEIS predictions are lower. CMAQ ozone predictions are similar and compare well with measurements using either MEGAN or BEIS. However, CMAQ-MEGAN overpredicts formaldehyde. CMAQ-BEIS SOC predictions are lower than observational estimates for every sample. CMAQ-MEGAN underpredicts SOC ∼ 80% of the time, despite overprediction of precursor VOCs. CMAQ-MEGAN isoprene predictions improve when prognostically predicted solar radiation is replaced with the GEWEX satellite product. CMAQ-BEIS does not exhibit similar photosensitivity.

Effects of Beijing Olympics control measures on reducing reactive hydrocarbon species

Stringent air-quality control measures were implemented for the 2008 Beijing Olympic Games. This large-scale manmade experiment provided an opportunity to evaluate the effectiveness of measures to reduce the reactivity of hydrocarbons (HCs) from emission sources, which is important for ground-level ozone abatement. Photochemical initial concentrations (PICs), i.e., the levels of HCs from sources before undergoing chemical reactions, were calculated from ambient measurements. PICs obtained using the ratio method for HCs and the sequential reaction model for alkyl nitrates were in good agreement. Propene, 1-butene, iso-butene, trans-2-butene, cis-2-butene, trans-2-pentene, and m,p-xylene were identified as key reactive species in terms of their photochemical consumptions and correspondent ozone formation potentials (OFPs). During the Olympics and Paralympics, the PICs of these seven species were reduced by 27-66%, contributing 20% to the reduction in total PICs and 60% to the reduction in total OFP compared with June levels. Source apportionments from the chemical mass balance model indicated that gasoline vehicle exhaust was the predominant contributor to the key reactive species (45-78%). Reductions of gasoline vehicle exhaust during the Olympics and Paralympics explained 53-77% and 59-68% of the reductions in PICs of the key reactive HCs and total OFP, respectively.

Inter-comparison of laser photoacoustic spectroscopy and gas chromatography techniques for measurements of ethene in the atmosphere

Laser photoacoustic spectroscopy (LPAS) is highly suitable for the detection of ethene in air due to the overlap between its strongest absorption lines and the wavelengths accessible by high-powered CO2 lasers. Here, we test the ability of LPAS to measure ethene in ambient air by comparing the measurements in urban air with those from a gas chromatography flame-ionization detection (GC-FID) instrument. Over the course of several days, we obtained quantitative agreement between the two measurements. Over this period, the LPAS instrument had a positive offset of 330 +/- 140 pptv (parts-per-trillion by volume) relative to the GC-FID instrument, possibly caused by interference from other species. The detection limit of the LPAS instrument is currently estimated around 1 ppbv and is limited by this offset and the statistical noise in the data. We conclude that LPAS has the potential to provide fast-response measurements of ethene in the atmosphere, with significant advantages over existing techniques when measuring from moving platforms and in the vicinity of emission sources.

Temporal changes in U.S. benzene emissions inferred from atmospheric measurements

The 1990 Clean Air Act Amendments required the United States Environmental Protection Agency (U.S. EPA) to enact stricter regulations aimed at reducing benzene emissions. In an effort to determine whether these new regulations have been successful in reducing atmospheric benzene concentrations, we have evaluated benzene-to-acetylene ratios from data sets spanning nearlythree decades, collected during several field studies and from the U.S. EPA's Photochemical Assessment Monitoring Station (PAMS) network. The field-study data indicate a decrease in benzene relative to acetylene of approximately 40% from 1994 to 2002. This corresponds to a decrease in benzene alone of approximately 56% over the same period. In contrast, the PAMS data exhibit high interannual variability with no discernible trend. This discrepancy is attributed to measurement problems in the PAMS data sets.

Distributions and source apportionment of ambient volatile organic compounds in Beijing city, China

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 microg/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.

Source identification of volatile organic compounds in Houston, Texas

The complexity of the volatile organic compound (VOC) mixture in the Houston area makes studies of the air quality in that area very challenging. In this paper, a novel factor analysis model, where the normal chemical mass balance model was augmented by a parallel equation that accounted for wind speed and direction, temperature, and weekend/weekday effects, was fitted with a multilinear engine (ME) to provide identification and apportionment of the VOC sources at the La Porte Municipal Airport site in Houston during the Texas Air Quality Study (TexAQS) 2000. The analysis determined the profiles and contributions of nine sources and the corresponding wind speed, wind direction, temperature, and weekend factors. The reasonableness of these results not only suggests the high resolving power of the expanded factor analysis model for source apportionment but also provides the novel and effective auxiliary information for more specific source identification. In addition, a new approach to estimate the measurement uncertainty and the details of determining the source number and dealing with missing values are also presented as important parts of the data analysis process. This study demonstrates the feasibility of the expanded model to identify sources in complex VOC systems and extract useful information for locating VOC emitters and controlling their emissions in the Houston area.

Observations of ozone formation in power plant plumes and implications for ozone control strategies

Data taken in aircraft transects of emissions plumes from rural U.S. coal-fired power plants were used to confirm and quantify the nonlinear dependence of tropospheric ozone formation on plume NO(x) (NO plus NO(2)) concentration, which is determined by plant NO(x) emission rate and atmospheric dispersion. The ambient availability of reactive volatile organic compounds, principally biogenic isoprene, was also found to modulate ozone production rate and yield in these rural plumes. Differences of a factor of 2 or greater in plume ozone formation rates and yields as a function of NO(x) and volatile organic compound concentrations were consistently observed. These large differences suggest that consideration of power plant NO(x) emission rates and geographic locations in current and future U.S. ozone control strategies could substantially enhance the efficacy of NO(x) reductions from these sources.