Volatile Organic Compounds Speciation Research Articles

A Common Representative Intermediates (CRI) mechanism for VOC degradation. Part 2: Gas phase mechanism reduction

The Common Representative Intermediates mechanism version 2 (CRI v2) is a reduced mechanism of intermediate complexity, traceable to the Master Chemical Mechanism version 3.1 (MCM v3.1), which couples with a detailed speciation of 112 emitted anthropogenic non-methane volatile organic compounds (VOCs). Systematic lumping techniques for the emitted anthropogenic VOC species have been used to reduce CRI v2, creating a series of five reduced variants, the performances of which have been evaluated against that of CRI v2 for a range of ambient conditions. For the initial reduction phases, minor emitted VOCs accounting for increasing proportions of the VOC mass emissions total, up to 20%, were redistributed into appropriate surrogates, and the redundant species and their associated chemistry were removed from the chemical mechanism. The surrogates were selected to maintain the chemical class of the redistributed VOCs within a number of VOC sub-categories, and aimed to preserve the ozone-forming ability of each category using the photochemical ozone creation potential (POCP) index as a criterion. This yielded three reduced mechanisms (CRI v2-R1, CRI v2-R2 and CRI v2-R3) and allowed respective reductions of up to 25% and 32% in the numbers of reactions and species, with no significant degradation in the overall performance of the mechanisms or in the relative contributions of the VOC sub-categories to ozone formation. More severe levels of reduction were also imposed, to limit the number of representative VOCs in each sub-catergory, with the choice of species taking account of their abundance in the detailed speciation, and the simplicity of the associated degradation mechanism. The POCP index was once again used as a guide to help optimise the overall ozone-forming ability of the VOC speciation. This yielded two further mechanisms (CRI v2-R4 and CRI v2-R5) with reductions of up to 53% and 55% in the numbers of reactions and species relative to CRI v2. These mechanisms display a degree of compromise in the ozone-forming ability of the VOC sub-categories, but retain a good level of overall performance. The most reduced variant (CRI v2-R5) uses 19 non-methane VOCs to represent the anthropogenic speciation, and is considered appropriate as a traceable reference mechanism for use in global chemistry-transport models.

Assessment of the Ozone Formation Potential from Pesticide Solvents Using a Mobile Ozone Chamber Assay Approach

Abstract The use of pesticides in California’s agricultural industry plays a role in air quality with emissions of organic compounds thought to contribute to the formation of ground level ozone. Ozone levels in many regions of California exceed the prescribed Federal and State standards every year. The actual contribution from pesticide applications (as well as other agricultural sources) is largely unknown, and relies on assumptions of reactivity and tendency to evaporate. Progress on accurate determinations of either parameter is limited by many factors, including the proprietary nature of formulations. We have developed an approach which can measure the ozone formation potential of many agricultural sources, in the field. This approach was previously validated and described during a recently completed and published study of emissions from dairy cattle, their feed, as well as their fresh waste. With accompanying measurements of the most abundant volatile organic compounds (VOCs) involved there, we showed agreement between laboratory studies, field measurements, and a computer model of atmospheric photochemical reactions that improves upon past efforts, which were limited to urban/industrial VOCs. Our goal is to reach the same level of understanding for VOCs contained in pesticide formulations. Two sets of field experiments were performed to assess the ozone formation potential of pesticide solvents using a set of transportable smog chambers in the summer of 2007. The first set of experiments were conducted for a solvent-based emulsifiable concentrate (EC) base-spray on a one-acre bare field, and the second set of experiments were conducted for an agricultural application of Lorsban 4E in a three-acre citrus orchard. By comparing the upwind and downwind measurements, the experiments indicated that the emission of pesticide solvent after field application led to increased ozone formation. After a 180 min UV exposure, the ozone formation potential measured at the downwind side averaged 14 ppb higher than that of upwind air, while the average difference was around 3 ppb for background levels on both the day before and the day after pesticide spray. Laboratory experiments were also conducted for different doses of EC base with various levels of nitrogen oxides using the transportable smog chambers. The experimental isopleth demonstrates that VOCs emitted from the EC base could result in high ozone formation. Future work will provide full VOC speciation and application of the results in a regional photochemical model to predict ozone impacts.

Source impacts by volatile organic compounds in an industrial city of southern Taiwan

This study investigates source impacts by airborne volatile organic compounds (VOC) at two sites designated for traffic and industry, in the largest industrial area Kaohsiung, southern Taiwan. The samples were collected at the two sites simultaneously during rush and non-rush hours in summer and autumn seasons. Same pattern of VOC groups were found at both sites: most abundant aromatics (78–95%) followed by alkanes (2–16%) and alkenes (0–6%). The BTEX concentration measured at the two sites ranged from 69 to 301 ppbC. Toluene, isopentane, ethylbenzene, and benzene were found to be the most abundant species. Speciation of VOCs was characterized with several skills including principal component factor analysis and BTEX characteristic ratios. Each of the resulted principal factors at the two sites explained over 80% of the VOCs data variance, and indicated that both of the sampling sites were influenced by both traffic and industrial sources with separately different levels. The remarkable patterns of the first two factors described not only the similarity but also the discrepancy at the two sampling sites, in terms of the source impacts. The high T/B ratios (7.56–14.25) observed at the industrial site implied the important impact from mobile emissions. The indicators, m,p-xylene/benzene and o-xylene/benzene, also confirmed the potential source of motor vehicles at both of the sampling sites. Air age assessment showed that more than half of the total observations located in the domain of fresh air. Low X/E ratios implied somewhat aged air mass transported to the sampling sites. The industrial site might not only encounter emissions from the industry sources, but also under unavoidable impact from the traffic sources.

Volatile Organic Compound (VOC) measurements in the Pearl River Delta (PRD) region, China

Abstract. We measured levels of ambient volatile organic compounds (VOCs) at seven sites in the Pearl River Delta (PRD) region of China during the Air Quality Monitoring Campaign spanning 4 October to 3 November 2004. Two of the sites, Guangzhou (GZ) and Xinken (XK), were intensive sites at which we collected multiple daily canister samples. The observations reported here provide a look at the VOC distribution, speciation, and photochemical implications in the PRD region. Alkanes constituted the largest percentage (>40%) in mixing ratios of the quantified VOCs at six sites; the exception was one major industrial site that was dominated by aromatics (about 52%). Highly elevated VOC levels occurred at GZ during two pollution episodes; however, the chemical composition of VOCs did not exhibit noticeable changes during these episodes. We calculated the OH loss rate to estimate the chemical reactivity of all VOCs. Of the anthropogenic VOCs, alkenes played a predominant role in VOC reactivity at GZ, whereas the contributions of reactive aromatics were more important at XK. Our preliminary analysis of the VOC correlations suggests that the ambient VOCs at GZ came directly from local sources (i.e., automobiles); those at XK were influenced by both local emissions and transportation of air mass from upwind areas.

The speciation of volatile organic compounds (VOCs) from motorcycle engine exhaust at different driving modes

This study investigated the emissions of volatile organic compound (VOC) from motorcycle engine exhaust at different driving modes on a dynamometer. The speciations and the ozone formation potential of VOC samples also had been investigated by GC/MS and maximum increment reactivity (MIR), respectively. Both brand new and in-use motorcycles were tested in this study. The tested motorcycles include 2-stroke and 4-stroke engines. There are totally 48 VOC compounds identified in this study. Only the VOC species with C 3–C 9 were identified successfully. Experimental results indicated that isopentane, toluene, m, p-xylene, n-pentane, 2-methylpentane, 3-methylpentane, benzene, n-heptane and methylheptane were the major VOC speciations in the motorcycle engine exhaust. The amount of VOC emissions of the in-use 2-stroke motorcycles was 5 times that of the new 2-stroke motorcycles and the in-use 4-stroke motorcycles was 15 times that of the new 4-stroke motorcycles during the whole cycle. The amount of VOC speciation concentration during idle and deceleration stages was higher than those during the acceleration and cruising modes. However, the emission rate of VOCs at various driving modes tested on a dynamometer had not been precised enough due to the inconsistent variation of volume efficiency of motorcycle engine. These data shows a clear distinct emission rate of VOC at various driving modes. Besides, alkanes and aromatics were the major VOC speciation groups in the motorcycle engine exhaust. The amount of VOCs contributed from 23% to 76% THC for the four types motorcycle. Great variation of VOC/THC were found among new and in-use motorcycle. The ozone formation potential of a 2-strokes engine was higher than that of a 4-stroke engine. The ozone formation potential of in-use motorcycles were also clear higher than those of new motorcycles.

Volatile organic compounds (VOCs) emitted from 40 Mediterranean plant species:: VOC speciation and extrapolation to habitat scale

Forty native Mediterranean plant species were screened for emissions of the C5 and C10 hydrocarbons, isoprene and monoterpenes, in five different habitats. A total of 32 compounds were observed in the emissions from these plants. The number of compounds emitted by different plant species varied from 19 ( Quercus ilex) to a single compound emission, usually of isoprene. Emission rates were normalised to generate emission factors for each plant species for each sampling event at standard conditions of temperature and light intensity. Plant species were categorised according to their main emitted compound, the major groups being isoprene, α-pinene, linalool, and limonene emitters. Estimates of habitat fluxes for each emitted compound were derived from the contributing plant species’ emission factors, biomass and ground cover. Emissions of individual compounds ranged from 0.002 to 505 g ha −1 h −1 (camphene from garrigue in Spain in autumn and isoprene from riverside habitats in Spain in late spring; respectively). Emissions of isoprene ranged from 0.3 to 505 g ha −1 h −1 (macchia in Italy in late spring and autumn; and riverside in Spain in late spring; respectively) and α-pinene emissions ranged from 0.51 to 52.92 g ha −1 h −1 (garrigue in Spain in late spring; and forest in France in autumn; respectively). Habitat fluxes of most compounds in autumn were greater than in late spring, dominated by emissions from Quercus ilex, Genista scorpius and Quercus pubescens. This study contributes to regional emission inventories and will be of use to tropospheric chemical modellers.

Emissions of ozone precursors from stationary sources:: a critical review

This paper discusses and critiques methods used to estimate emissions of, and create both aggregate and detailed modeling inventories for, nitrogen oxides (NO x ), volatile organic compounds (VOC) and carbon monoxide (CO), the main pollutants involved in ozone formation. Emissions of sulfur dioxide (SO 2) and methods to project emissions into the future are also briefly discussed. Many improvements have been made in emissions inventories over the past decade. For example, the required use of continuous emission monitors (CEMS) has produced site-specific emissions estimates from almost all US electric utility power plants, which are the major stationary source of NO x . However, many data quality issues remain. For example, the overall quality of standardized emission factors is very poor. In addition, uncertainties have been introduced by use of simplistic assumptions on the existent level of emission control. Even the use of CEMS has not eliminated uncertainty in emissions from power plants, because methods to deal with missing data can introduce bias. Emissions data for Mexico are not comprehensive, making ozone modeling in US border regions difficult. Data for VOC speciation is outdated, and crude data is often used to disaggregate emissions to the fine level of spatial and temporal detail needed for atmospheric modeling. It is difficult to make general statements about the importance of each of these problems, because there are no reliable estimates of the overall uncertainty of emissions values, and because the impact of emission inventory errors is very site specific. The Emissions Inventory Improvement Program (EIIP) initiated by the US Environmental Protection Agency promises to enhance the quality of future inventories, mainly through communication of best practices among state agencies. Further inventory improvement efforts must be focused on problems that most strongly influence poor prediction of ozone concentrations. Targets for improvement could be based on comparison of photochemical modeling results to observed concentrations, coupled with other techniques that better explain source-receptor relationships.

Impact of California Reformulated Gasoline on Motor Vehicle Emissions. 2. Volatile Organic Compound Speciation and Reactivity

This paper addresses the impact of California phase 2 reformulated gasoline (RFG) on the composition and reactivity of motor vehicle exhaust and evaporative emissions. Significant changes to gasoline properties that occurred in the first half of 1996 included an increase in oxygen content; decreases in alkene, aromatic, benzene, and sulfur contents; and modified distillation properties. Vehicle emissions were measured in a San Francisco Bay Area roadway tunnel in summers 1994−1997; gasoline samples were collected from local service stations in summers 1995 and 1996. Equilibrium gasoline headspace vapor composition was calculated from measured liquid gasoline composition. Addition of methyl tert-butyl ether (MTBE) and reduction of alkenes and aromatics in gasoline between summers 1995 and 1996 led to corresponding changes in the composition of gasoline headspace vapors. Normalized reactivity of liquid gasoline and headspace vapors decreased by 23 and 19%, respectively. Ozone formation should be reduced bec...

Scaling of Infrared Remote Sensor Hydrocarbon Measurements for Motor Vehicle Emission Inventory Calculations

Infrared (IR) remote sensors calibrated with propane understate volatile organic compound (VOC) concentrations in vehicle exhaust by 30−70% when compared to flame ionization detectors (FID). The difference depends on VOC composition and arises because many organic compounds in vehicle exhaust absorb less IR radiation than propane on a per-carbon basis. This study demonstrates an approach for scaling infrared measurements to reflect more accurately total exhaust VOC emissions from on-road motor vehicle fleets. Infrared versus flame ionization detector response to individual VOC was measured in the laboratory for methyl tert-butyl ether and a range of alkanes, alkenes, and aromatics that are prominent in vehicle exhaust. Overall IR/FID response to real exhaust mixtures was calculated by summing the response contributions of all individual VOC constituents. Average IR/FID response factors were calculated for typical on-road vehicle fleets based on VOC speciation profiles measured in several U.S. roadway tunnels. Results indicate that hydrocarbon concentrations measured by remote sensors with 3.4 μm filters should be multiplied by a factor of 2.0 ± 0.1 for light-duty vehicles using either California or federal reformulated gasoline blends and by 2.2 ± 0.1 when conventional gasoline is used.