Source characterization of ozone precursors by complementary approaches of vehicular indicator and principal component analysis

Measurements of speciated non-methane hydrocarbons (NMHCs) were conducted in an ozone non-attainment metropolis with pronounced industrial emissions in addition to traffic ones. Highly variable and complex natures of industrial sources make their composition profiles difficult to determine. In the circumstances of no reliable source profiles, two simple complementary approaches were attempted to characterize sources of NMHCs. First, a robust vehicular indicator, 3-methylpentane (3MC5A), which is an intrinsic component of gasoline, was used to estimate contributions of traffic versus non-traffic sources for major NMHCs with high ozone-forming potentials (OFPs), such as ethene, toluene, xylene, isoprene, etc. Second, the method of principal component analysis (PCA) was employed to further discern non-traffic emissions into various source groups. A total of 454 ambient samples were sampled in the urban-industrial complex metropolis (Kaohsiung, Taiwan) to build up a large dataset to be tested by the two complementary approaches. It was found that four types of emissions, i.e., traffic, household fuel leakage, industrial, and biogenic, were responsible for the observed ambient NMHCs. The industrial contribution was significant for ethene and toluene (with 48–67% and 33–62%, respectively), whereas xylene was found to be mainly vehicular. In addition, isoprene revealed its biogenic nature. OFPs arising from vehicular, industrial and biogenic contributions could be further assessed for the purpose of emission control of NMHCs in the ozone non-attainment area.     

C2–C10 nonmethane hydrocarbons measured in Dallas,USA—Seasonal trends and diurnal characteristics

Nonmethane hydrocarbons (NMHCs) are important precursors of ozone and other photo oxidants. We presented continuous hourly average concentrations of 45 C₂–C₁₀ NMHCs measured in urban area of Dallas, USA from 1996 to 2004. Most of the selected compounds are good variables with less noise. The top 10 species with high ozone-generating potential were identified according to their concentrations and reactivities. The ambient concentrations of abundant anthropogenic emission hydrocarbons measured in Dallas were about 2–4 times of the background values measured in the remote areas with adjacent latitude. The time series for anthropogenic emission hydrocarbons showed an obvious seasonal cycle with relatively high concentration in winter and low concentration in summer. The sinusoidal function with a linearly decreasing factor could well fit the time series of NMHCs. The phase of seasonal cycle for the aromatic hydrocarbons of toluene, m/p xylene and o-xylene that might come from both vehicle emission and solvent utilities evaporation was about 1 month earlier than that for alkanes and alkenes that mainly came from vehicle emission. Ambient NMHCs in Dallas decreased with a stable rate during 1996–2004. For most of compounds with high ozone-generating potential, the rate of ambient concentration decrease was higher or much higher than the rate of volatile organic compounds (VOCs) source emission reduction estimated by EPA's National Emission Inventory. On weekdays, the morning hydrocarbon concentration peak was coincident with morning traffic rush time in Dallas. Another concentration peak was delayed to afternoon traffic rush time. The characteristics of VOCs sources, photochemical removal processes and atmospheric dilution could be interpreted by the diurnal variations of benzene/ethylbenzene (B/E), toluene/ethylbenzene (T/E) and xylene/ethylbenzene (X/E). The ratio of VOC/NO_x measured in Dallas was substantially smaller than that calculated for USA cities. Ozone formation in Dallas was VOC sensitive.     

Characteristics and diurnal variations of NMHCs at urban,suburban, and rural sites in the Pearl River Delta and a remote site in South China

The Pearl River Delta (PRD) is one of the most industrialized and urbanized regions in China. With rapid growth of the economy, it is suffering from deteriorating air quality. Non-methane hydrocarbons (NMHCs) were investigated at urban and suburban sites in Guangzhou (GZ), a rural site in PRD and a clean remote site in South China, in April 2005. Additional roadside samples in GZ and Qingxi (QX, a small industrial town in PRD), ambient air samples at the rooftop of a printing factory in QX and exhaust samples from liquefied petroleum gas (LPG)—fueled taxis in GZ were collected to help identify the source signatures of NMHCs. A large fraction of propane (47%) was found in exhaust samples from LPG-fueled taxis in GZ and extremely high levels of toluene (2.0–3.1 ppmv) were found at the rooftop of the printing factory in QX. Vehicular and industrial emissions were the main sources of NMHCs. The effect of vehicular emission on the ambient air varied among the three PRD sites. The impact of industrial emissions was widespread and they contributed greatly to the high levels of aromatic hydrocarbons, especially toluene, at the three PRD sites investigated. Leakage from vehicles fueled by LPG contributed mainly to the high levels of propane and n-butane at the urban GZ site. Ethane and ethyne from long-range transport and isoprene from local biogenic emission were the main contributors to the total hydrocarbons at the remote site. Diurnal variations of NMHCs showed that the contribution from vehicular emissions varied with traffic conditions and were more influenced by fresh emissions at the urban site and by aged air at the suburban and rural sites. Isoprene from biogenic emission contributed largely to the ozone formation potential (OFP) at the remote site. Ethene, toluene and m/p-xylene were the main contributors to the OFP at the three PRD sites.     

Mixing ratios of volatile organic compounds (VOCs) in the atmosphere of Karachi,Pakistan

Mixing ratios of carbon monoxide (CO), methane (CH₄), non-methane hydrocarbons, halocarbons and alkyl nitrates (a total of 72 species) were determined for 78 whole air samples collected during the winter of 1998–1999 in Karachi, Pakistan. This is the first time that volatile organic compound (VOC) levels in Karachi have been extensively characterized. The overall air quality of the urban environment was determined using air samples collected at six locations throughout Karachi. Methane (6.3 ppmv) and ethane (93 ppbv) levels in Karachi were found to be much higher than in other cities that have been studied. The very high CH₄ levels highlight the importance of natural gas leakage in Karachi. The leakage of liquefied petroleum gas contributes to elevated propane and butane levels in Karachi, although the propane and butane burdens were lower than in other cities (e.g., Mexico City, Santiago). High levels of benzene (0.3–19 ppbv) also appear to be of concern in the Karachi urban area. Vehicular emissions were characterized using air samples collected along the busiest thoroughfare of the city (M.A. Jinnah Road). Emissions from vehicular exhaust were found to be the main source of many of the hydrocarbons reported here. Significant levels of isoprene (1.2 ppbv) were detected at the roadside, and vehicular exhaust is estimated to account for about 20% of the isoprene observed in Karachi. 1,2-Dichloroethane, a lead scavenger added to leaded fuel, was also emitted by cars. The photochemical production of ozone (O₃) was calculated for CO and the various VOCs using the Maximum Incremental Reactivity (MIR) scale. Based on the MIR scale, the leading contributors to O₃ production in Karachi are ethene, CO, propene, m-xylene and toluene.     

Pollution characteristics of ambient volatile organic compounds (VOCs) in the southeast coastal cities of China

With the rapid urbanization, the southeast coastal cities of China are facing increasing air pollution in the past decades. Large emissions of VOCs from vehicles and petrochemical factories have contributed greatly to the local air quality deterioration. Investigating the pollution characteristics of VOCs is of great significance to the environmental risk assessment and air quality improvement. Ambient VOC samples were collected simultaneously from nine coastal cities of southeast China using the Tedlar bags, and were subsequently preprocessed and analyzed using a cryogenic preconcentrator and a gas chromatography–mass spectrometry system, respectively. VOC compositions, spatial distributions, seasonal variations and ozone formation potentials (OPFs) were discussed. Results showed that methylene chloride, toluene, isopropyl alcohol and n-hexane were most abundant species, and oxygenated compounds, aromatics and halogenated hydrocarbons were most abundant chemical classes (62.5–95.6 % of TVOCs). Both industrial and vehicular exhausts might contribute greatly to the VOC emissions. The VOC levels in the southeast coastal cities of China were sufficiently high (e.g., 6.5 μg?m^?3 for benzene) to pose a health risk to local people. A more serious pollution state was found in the southern cities of the study region, while higher VOC levels were usually observed in winter. The B/T ratio (0.26?±?0.09) was lower than the typical ratio (ca. 0.6) for roadside samples, while the B/E (1.6–7.6) and T/E (7.2–26.8) ratios were higher than other cities around the world, which indicated a unique emission profile in the study region. Besides, analysis on ozone formation potentials (OFPs) indicated that toluene was the most important species in ozone production with the accountabilities for total OFPs of 22.6 to 59.6 %.     

Real-world vehicle emissions and VOCs profile in the Taipei tunnel located at Taiwan Taipei area

An in situ field experiment was conducted in a highway road tunnel in the Taipei City to determine the motor vehicle emission factors (EF) of different kinds of air pollution species. These are carbon monoxide (CO), oxides of nitrogen (NO_x), non-methane hydrocarbons (NMHC) and VOCs species. About 56 species of VOCs were sampled by canister sampler and followed by the GC-MS analyzing. Furthermore, the tunnel-drafting rate was determined by SF₆ tracer method.The EF for the highway vehicles determined from this experiment are 3.64, 0.90, 0.44 and 0.24 gm km⁻¹ veh⁻¹ for CO, NO_x, NMHC and the totally measured VOCs, respectively. A comparison of the EFs from the road tunnel experiment to the estimates by the USEPA MOBILE5b (M5b) and the modified Taiwan EPA MOBILE-TAIWAN2.0 (MT2.0) provides a first-hand evaluation of the model characteristics. M5b and MT2.0 both tend to underpredict CO by 10% and 20%, respectively. While M5b overpredicts NO_x and NMHC by 40% and 20%, respectively; MT2.0 has fairly good predictions for these two species. From the GC-MS analysis of the canister samples, it was found that the most abundant species from the traffic-emitted VOCs in Taipei road tunnel are toluene, ethene and 1,2,4-trimethyl-benzene (1,2,4-TMB) by the weight basis. However, ethene, acetylene and toluene are the most abundant in VOCs based on volume. The VOCs’ weight composition in terms of the carbon bond classification is 28% by the paraffins, 33% by the olefins and 39% by the aromatics, respectively. In order to evaluate the ozone formation potential from the typical road emission in Taipei area, the maximum increment reactivity is calculated. It was found that about 1015 mg of O₃ is induced by per vehicle per kilometer traveled emission. Among them, ethene, 1,2,4-TMB and propene from the road vehicle's emission contribute most to the ozone-formation reactivity.     

Photochemical ozone creation potentials for oxygenated volatile organic compounds: sensitivity to variations in kinetic and mechanistic parameters

The sensitivity of Photochemical Ozone Creation Potentials (POCP) to a series of systematic variations in the rates and products of reactions of radical intermediates and oxygenated products is investigated for the C₄ alcohols, 1-butanol (n-butanol) and 2-methyl-1-propanol (i-butanol), using the recently developed Master Chemical Mechanism (MCM) as the base case. The POCP values are determined from the calculated formation of ozone in the boundary layer over a period of approximately five days along an idealised straight line trajectory, using a photochemical trajectory model and methodology described in detail previously. The results allow the relative impacts on calculated ozone formation of various classes of chemical reaction within the degradation chemistry to be assessed. The calculated POCP is found to be very insensitive to many of the changes investigated. However, it is found to be sensitive to variations in the rate coefficient for the initiating reaction with OH (k_OH), although the sensitivity decreases with increasing k_OH. The POCP appears to vary approximately linearly with k_OH at low values (i.e. k_OH less than ca. 4×10^-13 cm³ molecule^-1 s^-1), whereas at high reactivities (i.e. k_OH greater than ca. 4×10^-11 cm³ molecule^-1 s^-1), the calculated POCP value is comparatively insensitive to the precise value of k_OH. The POCP is also very sensitive to mechanistic changes which influence the yields of unreactive oxygenated products (i.e. those with OH reactivities below ca. 10^-12 cm³ molecule^-1 s^-1), for example acetone. The propensity of the organic compound to produce organic nitrates (which act as comparatively unreactive reservoirs for free radicals and NO_x) also appears to have a notable influence on the calculated POCP. Recently reported information relevant to the degradation of oxygenated VOCs is then used to update the chemical schemes for the 17 alcohols and glycols, 10 ethers and glycol ethers, and 8 esters included in the MCM, and new schemes are incorporated for dimethoxy methane (CH₃OCH₂OCH₃) and dimethyl carbonate (CH₃OC(O)OCH₃), which are proposed fuel additives. New or updated POCP values are calculated for all 37 oxygenated VOCs and, where applicable, these are compared with the previous POCP values and reported Maximum Incremental Reactivity (MIR) values.     

Evaluation of non-methane hydrocarbon (NMHC) emissions based on an ambient air measurement in Tokyo area,Japan

Non-methane hydrocarbons (NMHCs) are known to have an important role on air quality due to their high reactivity. NMHC analysis has been performed on 148 ambient air samples collected at five different sites in the Kanto area (Tokyo metropolitan area and surrounding six prefectures) of Japan in summer and winter of 2008, and fifty NMHCs have been determined and quantified. A field measurement campaign has been conducted at one of the busiest intersections in Tokyo metropolitan area in winter of 2008. NMHC emissions are evaluated through comparison of distributions of individual NMHCs emitted from motor vehicles, which are estimated from the measurements, with those determined from the current emissions inventory. The comparison revealed that the measured distributions of acetylene, ethylene and toluene showed a good agreement with those estimated from the emissions inventory (the values estimated from the measurements are a factor of 1.5, 0.56 and 2.3 larger than the emissions inventory in median, respectively), however, propane and isobutane are found to be significantly underestimated in the emissions inventory (the measured values were a factor of 18 and 5.1 larger than the emissions inventory, respectively). The significant underestimate of propane can be explained by that the current emissions inventory does not consider emissions from liquefied propane gas (LPG) fueled vehicles. However, for isobutane, reasons for the underestimate are still unclear. Another field measurement has been conducted in summer of 2008, where the air samples have been collected at three different sites on the ground and by a helicopter as well. Remarkable high concentrations of 1-butene and cis- and trans-2-butenes have been sporadically observed in the samples collected at Urayasu in the coastal area of Tokyo bay. Calculated propylene equivalent (PE) concentrations of butenes revealed that those have a significantly important role in ozone formation when the air plume is affected by emissions from their emission sources. The PE concentrations of butenes varied from 0.1 to 39 ppbC, and accounted for 1.5–75% of total PE concentrations at Urayasu. Most of the continuous air quality monitoring stations does not record concentrations of individual hydrocarbons, therefore, the importance of reactive and low concentration hydrocarbon such as butenes might be overlooked in the current emissions inventory and/or air quality model. In this paper, the reliability of NMHC emissions is evaluated based on the field measurements. Their possible impacts on air quality in the Kanto area are discussed as well, based on the calculated propylene equivalent concentrations.     

A new condensed toluene mechanism for Carbon Bond: CB05-TU

Toluene is ubiquitous in urban atmospheres and is a precursor to tropospheric ozone and aerosol (smog). An important characteristic of toluene chemistry is the tendency of some degradation products (e.g., cresols and methyl-catechols) to form organic nitro and nitrate compounds that sequester NOx (NO and NO₂) from active participation in smog formation. Explaining the NOx sinks in toluene degradation has made mechanism development more difficult for toluene than for many other organic compounds. Another challenge for toluene is explaining sources of radicals early in the degradation process. This paper describes the development of a new condensed toluene mechanism consisting of 26 reactions, and evaluates the performance of CB05 with this new toluene scheme (Toluene Update, TU) against 38 chamber experiments at 7 different environmental chambers, and provides recommendations for future developments. CB05 with the current toluene mechanism (CB05-Base) under-predicted the maximum O₃ and O₃ production rate for many of these toluene–NOx chamber experiments, especially under low-NOx conditions ([NOx]_t=0 < 100 ppb). CB05 with the new toluene mechanism (CB05-TU) includes changes to the yields and reactions of cresols and ring-opening products, and showed better performance than CB05-Base in predicting the maximum O₃, O₃ formation rate, NOx removal rate and cresol concentration. Additional environmental chamber simulations with xylene–NOx experiments showed that the TU mechanism updates tended to improve mechanism performance for xylene.     

VOC concentration profiles in an ozone non-attainment area: A case study in an urban and industrial complex metroplex in southern Taiwan

VOCs are important precursors of the atmospheric ozone formation species. This study investigated the airborne concentrations of 52 VOCs at two air quality monitoring stations, Daliao and Tzouying, during wintertime in southern Taiwan. Airborne VOCs samples were taken in stainless steel canisters four times per day and analyzed via gas chromatography/mass spectrometry. Maximum increment reactivity (MIR) was used to evaluate the ozone formation potential in this ozone non-attainment region. Toluene, propane, isopentane, propene, n-butane, n-pentane and isoprene contributed 78–79% of the 52 VOCs in Daliao. Toluene, 1-butene, isopentane, propene, propane, n-undecane, and n-butane contributed 71–77% of the 52 VOCs in Tzouying. The VOCs concentrations were higher in Daliao due to the high toluene emissions from a paint plant and a solvent plant in the nearby industrial district. The 24-h VOC concentrations averaged 25 ppb higher in Tzouying than in Daliao. The ozone formation potential of airborne VOCs was 1687–2730 and 1717–2261 μg-O₃/g-VOCs in Daliao and Tzouying, respectively. Ozone concentrations in Tzouying were 44 ppb higher than in Daliao during the 1200–1600 sampling period.     

Modeling smog chamber measurements of incremental reactivities of volatile organic compounds

A series of experiments performed at the GM chamber facility provided useful data for the evaluation of two current chemical mechanisms used in airshed models (SAPRC97 and SAPRC93 mechanisms) and a test of their predictions of maximum incremental reactivities which describe the change in ozone caused by adding a small amount of a compound to a polluted urban mixture under high-NO_x conditions. In general, the SAPRC97 detailed mechanism performed well in simulating the volatile organic compound (VOC) reactivity experiments for most test species; however, it had a tendency to underpredict incremental reactivities. For base-case runs containing a nine-component urban-surrogate mixture under high-NO_x conditions, where maximum concentrations of either O₃ or the smog produced (SP=the initial NO oxidized plus the ozone produced) were not attained during a 12-h irradiation, the SAPRC97 performed well while the SAPRC93 underestimated SP or O₃ significantly. Under low-NO_x conditions where SP or O₃ maximums were attained, the SAPRC97 as well as the SAPRC93 underpredicted SP or O₃ for runs containing the urban-surrogate mixture. Simulations of incremental reactivity experiments and special chamber runs showed that the SAPRC97 mechanism performed poorly for n-octane and some aromatic isomers such as ethylbenzene and p-xylene, while it performed well for other aromatic isomers such as toluene, m-xylene and 1,3,5-trimethylbenzene. Although, additional chamber data for aromatic isomers is needed to further clarify the parameterized chemical mechanisms for aromatic isomers, the newer SAPRC97 mechanism appears to be much improved over the older SAPRC93 mechanism for simulating aromatic chemistry.     

Validation of in-situ measurements of volatile organic compounds through flask sampling and gas chromatography/mass spectrometry analysis

Continuous monitoring of ambient non-methane hydrocarbons (NMHCs) by automated gas chromatographs equipped with flame ionization detection (termed in-situ GC/FID) with hourly data resolution was instated in ozone non-attainment areas throughout Taiwan. Performance of these on-site in-situ GCs was validated by manual flask sampling, as well as by in-lab gas chromatography/mass spectrometry (GC/MS) analysis. More than 50 VOCs from C₂ to C₁₁ were analyzed by both methods. Ninety flask samples were collected in series near an in-situ GC monitoring station in order to closely compare with the in-situ measurements. Both time-series and scatter plots from the two methods are displayed and discussed. It was found that over-simplified, un-humidified single-point calibration leading to surface loss was responsible for the bias in the in-situ method, resulting in greater error in accuracy as VOC volatility decreased. Although this over-estimate of the concentrations was found across all target VOCs, both methods were able to consistently capture the variability of ambient VOCs, with R² values greater than 0.9 for most of the major VOCs.     

NMOC,ozone, and organic aerosol in the southeastern United States, 1999–2007: 1. Spatial and temporal variations of NMOC concentrations and composition in Atlanta,Georgia

Volatile organic compounds (VOCs) are emitted from anthropogenic and natural (biogenic) sources into the atmosphere. Characterizing their ambient mixing ratios or concentrations is a challenge because VOCs comprise hundreds of species, and accurate measurements are difficult. Long-term hourly and daily-resolution data have been collected in the metropolitan area of Atlanta, Georgia, a major city dominated by motor vehicle emissions. A series of observations of daily, speciated C₂–C₁₀ non-methane organic compounds (NMOC) and oxygenated hydrocarbons (OVOC) in mid-town Atlanta (Jefferson Street, JST) are compared with data from three urban-suburban sites and a nearby non-urban site. Annual-average mixing ratios of NMOC and OVOC at JST declined from 1999 through 2007. Downward trends in NMOC, CO, and NO_y corroborate expected emission changes as reflected in emission inventories for Atlanta’s Fulton County. Comparison of the JST NMOC composition with data from roadside and tunnel sampling reveals similarities to motor vehicle dominated samples. The JST annual average VOC-OH reactivities from 1999 to 2007 were relatively constant compared with the decline in annual-average NMOC mixing ratios. Mean reactivity at JST, in terms of concentration*k_OH, was approximately 40% alkenes, 22% aromatics, 16% isoprene and 6% other biogenics, 13% C₇–C₁₀ alkanes and 3% C₂-C₆ alkanes, indicating that biogenic NMOCs are important but not dominant contributors to the urban reactive NMOC mix. In contrast, isoprene constituted ～50% of the VOC-OH reactivities at two non-urban sites. Ratios of 24-hour average CO/benzene, CO/isopentane, and CO/acetylene concentrations indicate that such species are relatively conserved, consistent with their low reactivity. Ratios of more-reactive to less-reactive species show diurnal variability largely consistent with expected emission patterns, transport and mixing of air, and chemical processing.     

Assessment of reducing ozone forming potential for vehicles using liquefied petroleum gas as an alternative fuel

Liquefied petroleum gas (LPG) is currently used in a small fleet of taxis as an alternative fuel to gasoline in Taipei, Taiwan as part of an incentive program promoted by Taiwan EPA to improve urban air quality. Under the test procedure in accordance with the US FTP-75 protocol to simulate an average urban driving pattern, the exhaust from four LPG and four gasoline-powered vehicles was analyzed for the percent composition of NMHCs. Emission factors for individual NMHCs were apportioned from the emission factors of total hydrocarbon based on chemical composition of the exhaust from both types of vehicles. After adjusting for ozone formation potential (OFP) by maximum incremental reactivity, the average OFP for LPG vehicles was estimated to be only 52.8% (g-O₃/veh-km) of the gasoline vehicles, or 3.3% of ozone reduction in Taipei metropolitan area, should all taxis be converted to LPG fuel.Composition analysis of the local LPG revealed that propane, butane and isobutane were the three major components and negligible amounts of alkenes were also found. In addition, the leakage from a LPG service station was substantially smaller than from a gasoline service station because of the closed design with the LPG pumping systems.     

Diurnal and seasonal cycles of ozone precursors observed from continuous measurement at an urban site in Taiwan

Hourly measurement of 56 ozone precursors was conducted by a monitoring station located in a metropolitan area in central Taiwan. After nearly a year of continuous operation at this urban site, both diurnal and seasonal cycles of nonmethane hydrocarbons (NMHCs) were clearly observed, which was caused by the interplay between source, chemical loss, and meteorology. Selected species representing three different types of major sources namely the household fuel leakage, vehicular exhaust and gasoline evaporation, as well as biogenic emissions exhibit dramatic diurnal or seasonal cycles with each displaying its own unique characteristics.Ethane and propane, largely originated from leakage of natural gas or liquefied petroleum gases (LPG), showed concentrations elevating throughout the night and early morning, but began to decrease towards noon as the nocturnal temperature inversion elevated. Because of the lower chemical reactivity and somewhat more constant emissions than other measured target compounds, their diurnal cycles were presumably the direct reflection of the mixing height over the metropolitan area.For compounds originating from vehicular plus evaporative emissions such as benzene, which accounts for most of the monitored compounds, their diurnal cycles were also largely controlled by the variation in the height of temperature inversion.Of all the 56 species monitored, isoprene, an abundant biogenic species largely released by plants, showed distinct diurnal and seasonal cycles different from the other measured NMHCs. Its concentration usually peaked at noon in summer and fall when temperature and solar radiation reached their maximum level, demonstrating the close relationship of isoprene with photosynthesis.Seasonal variation was also clearly observed for the other NMHCs quantified. With the exception of isoprene, most species show higher average concentration in winter and lower in summer with the fall values being the intermediate, which presumably is caused by both the seasonal variation in HO abundance and the height of the temperature inversion.     

Characteristics of ambient C2–C11 non-methane hydrocarbons in metropolitan Nagoya,Japan

To understand the characteristics of non-methane hydrocarbon (NMHC) abundance in an urban air of Nagoya, one of the metropolitan areas of Japan, 48 species of C₂–C₁₁ NMHCs were measured with a measurement system, developed in this study, by using gas chromatography with flame ionization detection (GC/FID) continuously for one year from December 2003 to November 2004.Annual mean concentration of NMHCs in normal and propylene equivalent (PE) in Nagoya was compared with those in four urban areas of Seoul, London, Lille, and Dallas to extract characteristics of urban air. While the absolute values of the normal and PE concentrations of alkanes, alkenes, alkyne, and aromatics were significantly different among these urban areas, the proportions of each chemical group to the total NMHC were not so different.In Nagoya, the total normal concentration was high from November to February and low from June to August. The pattern of the seasonal variation was influenced mainly by that of alkanes. On the other hand, the total PE concentration was high from July to December and low from January to June. The pattern of the seasonal variation was influenced mainly by those of alkenes and aromatics. Particularly the normal concentration of isoprene was high from May to September because of large emission associated with activity of plants. As the results, in summer, the PE concentration of isoprene was especially high, and its contribution to the total NMHCs measured in this study was approximately 40%. The total PE concentrations were high in summer when the concentration of OH radicals is also high, suggesting that the productions of ozone and secondary organic aerosol (SOA) are likely to be promoted in summer of Nagoya.     

Source profiles of volatile organic compounds associated with solvent use in Beijing,China

Compositions of volatile organic compound (VOC) emissions from painting applications and printing processes were sampled and measured by gas chromatography–mass spectrometry/flame ionization detection (GC–MS/FID) in Beijing. Toluene and C8 aromatics were the most abundant species, accounting for 76% of the total VOCs emitted from paint applications. The major species in printing emissions included heavier alkanes and aromatics, such as n-nonane, n-decane, n-undecane, toluene, and m/p-xylene. Measurements of VOCs obtained from furniture paint emissions in 2003 and 2007 suggest a quick decline in benzene levels associated with formulation changes in furniture paints during these years. A comparison of VOC source profiles for painting and printing between Beijing and other parts of the world showed significant region-specific discrepancies, probably because of different market demands and environmental standards. We conducted the evaluation of the source reactivities for various VOC emission sources. The ozone formation potential (OFP) for unit mass of VOCs source emissions is the highest for paint applications. Substituting solvent-based paints by water-based in Beijing will lead to an OFP reduction of 152,000 tons per year, which is more than 1/4 of the OFPs for VOCs emissions from vehicle exhaust in the city.     

Measurement of surface ozone and its precursors in an urban area in South Brazil

Weekly and seasonal variations of surface ozone and their precursors – nitrogen oxides, carbon monoxide-associated with meteorological parameters (wind direction, temperature, solar radiation) – are reported. Measurements were performed continuously during 2006 at two sampling stations located in the metropolitan area of Porto Alegre, Brazil. Results have shown that O₃ concentrations remained almost constant between weekdays. Levels of NO_x precursors decreased especially on Sundays, due to lighter traffic. The seasonal variation has shown a maximum O₃ concentration during summer and spring while NO_x and NO₂ have maxima at the colder months. The daily cycle of highest ozone concentrations reveals a lower nightly level and an inverse relation between O₃ and NO_x, evidencing the photochemical formation of O₃. There are seasonal variation and source heterogeneity.     

Estimate of initial isoprene contribution to ozone formation potential in Beijing, China

Volatile organic compounds (VOCs) are important precursors of tropospheric ozone formation. Isoprene contributions to ozone formation by using ambient mixing ratios are generally underestimated because of rapid chemical losses. In this study, ambient mixing ratios of major VOC species were continuously measured at Peking university (PKU) and YUFA, urban and sub-urban sites in Beijing, the city that will host 2008 Olympic Games. The observed mixing ratios of methyl vinyl ketone (MVK), methacrolein (MACR) and isoprene were used to derive the mixing ratios of initial isoprene, which means the ambient isoprene level before it undergoes any photochemical reaction with OH radicals. The average mixing ratios of initial isoprene were 3.3±1.6 and 2.9±1.5 ppbv at PKU and YUFA sites, respectively. The percentages of initial isoprene in total initial VOCs were 10.8% at PKU site and 11.4% at YUFA site, in reasonable agreement with the isoprene contribution in total VOC emissions as derived from source inventories. Maximum increment reactivity (MIR) was used to evaluate the ozone formation potential (OFP) for major VOC species. The OFP for initial isoprene accounted for 23% of the total OFPs for all measured species, compared to 11% using ambient mixing ratios of isoprene at PKU site. Similarly, at YUFA site, the ambient measured isoprene and initial isoprene contributed 10% and 22%, respectively, to the OFPs for total measured VOCs. It seems that isoprene has similar contribution to ozone formation at both sites in Beijing city.