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.     

Methodologies for estimating disaggregated anthropogenic emissions--application to a coastal Mediterranean region of Spain

Regional estimates of both anthropogenic and biogenic emissions are important inputs for models of atmospheric chemistry. A disaggregated emissions inventory of all relevant pollutants for an area of 100 x 100 km2 centered in Burriana (Castellon, Spain) has been worked out. Time and spatial resolutions were hourly and 1 x 1 km2, respectively. Estimates were made for all relevant sources of anthropogenic emissions. The pollutants considered were SO2, NOx, NMVOCs (nonmethane volatile organic compounds), CH4, CO, CO2, N2O, and NH3. Thus, the emissions inventory includes up to 18 different NMVOCs. Emissions were computed for a typical sunny workday in June when strong photochemical activity could be expected. A "top-down" methodology was applied, taking as a starting point official annual and provincial estimates based on CORINAIR emission factors. This procedure is a very useful tool, particularly for those cases where a lack of sufficient local detailed information about the main emission-generating activities, such as road traffic, makes the use of a "bottom-up" approximation inadvisable. Moreover, updating these emission inventories is easier and they could be used to evaluate the impact of possible abatement strategies.     

Emission,speciation, and evaluation of impacts of non-methane volatile organic compounds from open dump site

Surface emission from Dhapa, the only garbage disposal ground in Kolkata, is a matter of concern to the local environment and also fuels the issues of occupational and environmental health. Surface emission of the Dhapa landfill site was studied using a flux chamber measurement for nonmethane volatile organic compounds (NMVOCs). Eighteen noncarbonyl volatile organic compounds (VOCs) and 14 carbonyl VOCs, including suspected and known carcinogens, were found in appreciable concentrations. The concentrations of the target species in the flux chamber were found to be significantly higher for most of the species in summer than winter. Surface emission rate of landfill gas was estimated by using two different approaches to assess the applicability for an open landfill site. It was found that the emissions predicted using the model Land GEM version 3.02 is one to two orders less than the emission rate calculated from flux chamber measurement for the target species. Tropospheric ozone formation has a serious impact for NMVOC emission. The total ozone-forming potential (OFP) of the Dhapa dumping ground considering all target NMVOCs was estimated to be 4.9E+04 and 1.2E+05 g/day in winter and summer, respectively. Also, it was found that carbonyl VOCs play a more important role than noncarbonyl VOCs for tropospheric ozone formation. Cumulative cancer risk estimated for all the carcinogenic species was found to be 2792 for 1 million population, while the total noncancer hazard index (HI) was estimated to be 246 for the occupational exposure to different compounds from surface emission to the dump-site workers at Dhapa.

Implications:This paper describes the real-time surface emission of NMVOCs from an open municipal solid waste (MSW) dump site studied using a flux chamber. Our study findings indicate that while planning for new landfill site in tropical meteorology, real-time emission data must be considered, rather than relying on modeled data. The formation of tropospheric ozone from emitted NMVOC has also been studied. Our result shows how an open landfill site acts as a source and adds to the tropospheric ozone for the airshed of a metropolitan city.     

Airshed Model Evaluation of Reactivity Adjustment Factors Calculated with the Maximum Incremental Reactivity Scale for Transitional-Low Emission Vehicles

Abstract

The California Air Resources Board recently adopted regulations for light- and medium-duty vehicles that require reductions in the ozone-forming potential or “reactivity,” rather than the mass, of nonmethane organic gas (NMOG) emissions. The regulations allow sale of all alternatively fueled vehicles (AFVs) that meet NMOG exhaust emission standards equivalent in reactivity to those set for vehicles fueled with conventional gasoline. Reactivity adjustment factors (RAFs), the ratio of the reactivity (per gram) of the AFV exhaust to that of the conventionally fueled vehicle (CFV), are used to correct the stringent exhaust emission standards. Complete chemical speciation of the exhaust and conversion of each NMOG species to an appropriate mass of ozone using the maximum incremental reactivity (MIR) scale of Carter determines the RAF. The MIR approach defines reactivity where NMOG control is the most effective strategy in reducing ozone concentrations, and assumes it is not important to define reactivity at other conditions, i.e., where NO_x is the limiting precursor.

This study used the Carnegie/California Institute of Technology airshed model to evaluate whether the RAF-adjusted AFV emissions result in ozone impacts equivalent to those of CFV emissions. A matrix of two ozone episodes in the South Coast Air Basin (SoCAB) of California, two base emission inventories, and exhaust emissions from three alternative fuels that meet the first level of the low emission vehicle standards bounds the expected range of conditions. Although very good agreement was found previously for individual NMOG species,² this study noted deviations of up to ±15 percent from the equal ozone impacts for any vehicle/fuel combination required by the California regulations. These deviations appear to be attributable to differences in spatial and temporal patterns of emissions between vehicle fleets, rather than a problem with the MIR approach. The first formally adopted RAF, a value of 0.41 for 85 percent methanol/15 percent gasoline-fueled vehicles, includes a 10 percent increase based on the airshed modeling. The correction to the RAF is different for other fuels and may be different for air basins other than the SoCAB.     

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.     

A Fuel-Based Motor Vehicle Emission Inventory

Abstract

A fuel-based methodology for calculating motor vehicle emission inventories is presented. In the fuel-based method, emission factors are normalized to fuel consumption and expressed as grams of pollutant emitted per gallon of gasoline burned. Fleet-average emission factors are calculated from the measured on-road emissions of a large, random sample of vehicles. Gasoline use is known at the state level from sales tax data, and may be disaggregated to individual air basins. A fuel-based motor vehicle CO inventory was calculated for the South Coast Air Basin in California for summer 1991. Emission factors were calculated from remote sensing measurements of more than 70,000 in-use vehicles. Stabilized exhaust emissions of CO were estimated to be 4400 tons/day for cars and 1500 tons/day for light-duty and medium- duty trucks, with an estimated uncertainty of ±20% for cars and ±30% for trucks. Total motor vehicle CO emissions, including incremental start emissions and emissions from heavy-duty vehicles were estimated to be 7900 tons/day. Fuelbased inventory estimates were greater than those of California's MVEI 7F model by factors of 2.2 for cars and 2.6 for trucks. A draft version of California's MVEI 7G model, which includes increased contributions from high-emitting vehicles and off-cycle emissions, predicted CO emissions which closely matched the fuel-based inventory. An analysis of CO mass emissions as a function of vehicle age revealed that cars and trucks which were ten or more years old were responsible for 58% of stabilized exhaust CO emissions from all cars and trucks.     

Vehicle emissions of radical precursors and related species observed in the 2009 SHARP campaign

The 2009 Study of Houston Atmospheric Radical Precursors (SHARP) field campaign had several components that yielded information on the primary vehicular emissions of formaldehyde (HCHO) and nitrous acid (HONO), in addition to many other species. Analysis of HONO measurements at the Moody Tower site in Houston, TX, yielded emission ratios of HONO to the vehicle exhaust tracer species NO_x and CO of 14 pptv/ppbv and 2.3 pptv/ppbv, somewhat smaller than recently published results from the Galleria site, although evidence is presented that the Moody Tower values should be upper limits to the true ratios of directly emitted HONO, and are consistent with ratios used in current standard emissions models. Several other Moody Tower emission ratios are presented, in particular a value for HCHO/CO of 2.4 pptv/ppbv. Considering only estimates of random errors, this would be significantly lower than a previous value, though the small sample size and possible systematic differences should be taken into account. Emission factors for CO, NO_x, and HCHO, as well as various volatile organic compounds (VOCs), were derived from mobile laboratory measurements both in the Washburn Tunnel and in on-road exhaust plume observations. These two sets of results and others reported in the literature all agree well, and are substantially larger than the CO, NO_x, and HCHO emission factors derived from the emission ratios reported from the Galleria site.

Implications: Emission factors for the species measured in the various components of the 2009 SHARP campaign in Houston, TX, including HCHO, HONO, CO, CO₂, nitrogen oxides, and VOCs, are needed to support regional air quality monitoring. Components of the SHARP campaign measured these species in several different ways, each with their own potential for systematic errors and differences in vehicle fleets sampled. Comparisons between data sets suggest that differences in sampling place and time may result in quite different emission factors, while also showing that different vehicle mixes can yield surprisingly similar emission factors.     

Comparison of the SCAQS Tunnel Study with Other On Road Vehicle Emission Data

The Van Nuys Tunnel experiment conducted in 1987 by Ingalls et al. (see A&WMA Paper 89-137.3), to verify automotive emission inventories as part of the Southern California Air Quality Study (SCAQS), gave higher CO and HC emission-rate values than expected on the basis of automotive-emission models—by factors of approximately 3 and 4, respectively. The CO/NO_X and HC/NO_X emission-rate ratios moreover were higher than expected—by similar factors (NO_X emission rates were about as expected). The purpose of the present paper is to review the literature on dynamometer and on-road (in tunnels and along roadways) testing of in-use vehicles, and on urban-air CO/HC/NO_X concentration ratios, to see whether the Van Nuys Tunnel results are reasonable in terms of previous experience. The conclusions are that (1) on-road CO and HC emissions higher than expected have been reported before, (2) on-road CO and HC emissions consistent with the Van Nuys Tunnel results have been reported before, and (3) on-road CO/NO_X and HC/NO_X emission-rate ratios higher than expected have been reported before. The Van Nuys Tunnel NO_X results actually are lower than in other on-road experiments, and the CO/NO_X and HC/NO_X ratios consequently are higher. The higher-than-predicted CO/NO_X and HC/NO_X ratios at Van Nuys and other on-road sites suggest richer operation on-road than predicted or than observed in the inuse- vehicle dynamometer tests which serve as the model inputs. Support for these suggestions and conclusions is found in comparison of urban-air and emission-inventory HC/NO_X ratios.     

The Impact of California Phase 2 Reformulated Gasoline on Real-World Vehicle Emissions

ABSTRACT

In mid-1996, California implemented Phase 2 Reformulated Gasoline (RFG). The new fuel was designed to further decrease emissions of hydrocarbons (HC_s), oxides of nitrogen (NO_x), carbon monoxide (CO), sulfur dioxide (SO₂), and other toxic species. In addition, it was formulated to reduce the ozone-forming potential of the HCs emitted by vehicles. Previous studies have observed that emissions from on-road vehicles can differ significantly from those predicted by mobile source emissions models, and so it is important to quantify the change in emissions in a real-world setting. In October 1995, prior to the introduction of California Phase 2 RFG, the Desert Research Institute (DRI) performed a study of vehicle emissions in Los Angeles' Sepulveda Tunnel. This study provided a baseline against which the results of a second experiment, conducted in July 1996, could be compared to evaluate the impact of California Phase 2 RFG on emissions from real-world vehicles. Compared with the 1995 experiment, CO and NO_x emissions exhibited statistically significant decreases, while the decrease in non-methane hydrocarbon emissions was not statistically significant.

Changes in the speciated HC emissions were evaluated. The benzene emission rate decreased by 27% and the overall emission rate of aromatic compounds decreased by 22% comparing the runs with similar speeds. Emissions of alkenes were virtually unchanged; however, emissions of combustion related unsaturates (e.g., acetylene, ethene) increased, while heavier alkenes decreased. The emission rate of methyl tertiary butyl ether (MTBE) exhibited a larger increase. Overall changes in the ozone-forming potential of the emissions were not significantly different, with the increased contributions to reactivity from paraffins, ole-fins, and MTBE being offset by a large decrease in reactivity due to aromatics.     

Boiler briquette coal versus raw coal: Part I--Stack gas emissions

Stack gas emissions were characterized for a steam-generating boiler commonly used in China. The boiler was tested when fired with a newly formulated boiler briquette coal (BB-coal) and when fired with conventional raw coal (R-coal). The stack gas emissions were analyzed to determine emission rates and emission factors and to develop chemical source profiles. A dilution source sampling system was used to collect PM on both Teflon membrane filters and quartz fiber filters. The Teflon filters were analyzed gravimetrically for PM10 and PM2.5 mass concentrations and by X-ray fluorescence (XRF) for trace elements. The quartz fiber filters were analyzed for organic carbon (OC) and elemental carbon (EC) using a thermal/optical reflectance technique. Sulfur dioxide was measured using the standard wet chemistry method. Carbon monoxide was measured using an Orsat combustion analyzer. The emission rates of the R-coal combustion (in kg/hr), determined using the measured stack gas concentrations and the stack gas emission rates, were 0.74 for PM10, 0.38 for PM2.5, 20.7 for SO2, and 6.8 for CO, while those of the BB-coal combustion were 0.95 for PM10, 0.30 for PM2.5, 7.5 for SO2, and 5.3 for CO. The fuel-mass-based emission factors (in g/kg) of the R-coal, determined using the emission rates and the fuel burn rates, were 1.68 for PM10, 0.87 for PM2.5, 46.7 for SO2, and 15 for CO, while those of the BB-coal were 2.51 for PM10, 0.79 for PM2.5, 19.9 for SO2, and 14 for CO. The task-based emission factors (in g/ton steam generated) of the R-coal, determined using the fuel-mass-based emission factors and the coal/steam conversion factors, were 0.23 for PM10, 0.12 for PM2.5, 6.4 for SO2, and 2.0 for CO, while those of the BB-coal were 0.30 for PM10, 0.094 for PM2.5, 2.4 for SO2, and 1.7 for CO. PM10 and PM2.5 elemental compositions are also presented for both types of coal tested in the study.     

Optimized combinations of abatement strategies for urban mobile sources

The maximum incremental reactivity (MIR) scale was chosen as a practical index for quantifying ozone-forming impacts. The integer linear and nonlinear programming techniques were employed as the optimization method to maximize MIR and volatile organic compound (VOC) reductions, and minimize ozone's marginal cost with varied control costs. Mobile vehicles were divided into nine categories according to the demands of decision makers and the distinctive features of local circumstance in metro-Taipei. The emission factor (EF) and vehicle kilometers traveled (VKT) of each kind of vehicle were estimated by MOBILE5B model via native parameters and questionnaires. Compressed natural gas (CNG) and inspection and maintenance (I/M) were the alternative control programs for buses and touring buses; liquefied petroleum gas (LPG), I/M, methanol, electrical vehicle (EV) were for taxis and low duty gasoline vehicles. EV, methanol, and I/M were the possible control methods for two-stroke and four-stroke engine motorcycles; I/M programs for low-duty diesel trucks, heavy-duty diesel trucks, and low-duty gasoline trucks. The results include the emission ratios of specific vehicle to all vehicles, the best combination of abated measures based on different objectives, and the marginal cost for ozone and VOC with varied control costs.     

An experimental investigation of incremental reactivities of volatile organic compounds

California has adopted a set of VOC reactivity factors for regulatory purposes that is based on a model of the ozone formation process. These incremental reactivity factors (derived by Carter) describe the amount of ozone each exhaust VOC will form under a certain set of conditions in an urban atmosphere. The main objective of this study is to measure reactivity factors using smog chamber experiments, and to compare the measurements to the Carter factors. A new facility was constructed explicitly for this study. The facility has four identical smog chambers and a temperature-controlled enclosure for the chambers. The chambers are irradiated using a set of filtered xenon arc lamps to approximate “sunlight”. The reactivities of 14 individual VOCs representative of those found in automobile exhaust and several mixtures of VOCs have been measured. The measured and Carter-reactivity factors were highly correlated, suggesting that the chemical model used by Carter accounts for the reactivities of a wide range of compounds with dramatically different uncertainties in their mechanisms. The measured results, in general, are consistent with the Carter-reactivity factors for comparing the relative reactivities of VOCs in the atmosphere. However, additional kinetic and mechanistic studies of many VOC species including aromatic isomers are needed to improve reactivity scales.     

Weekday/weekend differences in OH reactivity with VOCs and CO in Baltimore, Maryland

This study compared the first-order frequencies for OH associated with volatile organic compounds (VOCs) and CO (hereafter called OH reactivity with VOCs or CO), the product of the VOC or CO concentration, and their respective kOH value, on an average weekday with that on an average weekend day at a core urban site in Baltimore, MD. The average daytime concentrations were calculated for each of the 55 available Photochemical Assessment Monitoring Station (PAMS) VOCs using data from the Baltimore site. The data were sorted in descending order to highlight the important species based on concentration. The OH reactivity with VOCs was sorted in descending order to identify the important species based on the magnitude of the OH reactivity. A similar process was followed for the OH reactivity with CO. The contribution of the significant species to the weekday/weekend difference in OH reactivity was examined. The OH reactivity with C5H8 was the largest among the OH reactivity with the PAMS' VOCs and was the same on the weekday and weekend. The weekday/weekend difference in OH reactivity with VOCs was entirely due to differences in concentrations of the anthropogenic VOCs. The OH reactivity with VOCs was 11% larger on the weekday. When OH reactivity with CO was included, the OH reactivity was 13% larger on the weekday.     

Source profiles and ozone formation potentials of volatile organic compounds in three traffic tunnels in Kaohsiung,Taiwan

Twenty-five volatile organic compounds (VOCs) up to C10 were measured using Carbotrap multibed thermal adsorption tubes during the morning and afternoon rush hours on four different days in all three traffic tunnels in Kaohsiung, Taiwan. A gas chromatograph (GC) equipped with a flame-ionization detector (FID) was then used to analyze the VOCs. The analytical results show that VOC concentrations increase with traffic flow rate, and emission profiles in the three tunnels are mostly in the range C2-C6. In addition to the traffic conditions and vehicle type, the pattern of emissions in each tunnel was also influenced by other factors, such as vehicle age, nearby pollution sources, and the spatial or temporal variation of VOCs in the urban atmosphere. The ozone formation potential (OFP) in each tunnel was assessed based on the maximum incremental reactivities of the organic species, demonstrating that OFP increases with traffic flow rate. Vehicle distribution influences the contributions of organic group to OFP in a tunnel. Meanwhile, when ranked in descending order of contribution to OFP in all tunnels, the organic groups followed the sequence olefins, aromatics, and paraffins.     

Effects of reactive hydrocarbons on ozone formation in southern Taiwan

Ambient air samples were collected at 13 air quality monitoring stations in Kaohsiung city, Kaohsiung county, and Pingtung county (KKP) to investigate the composition and spatial distribution of C₂–C₁₀ non-methane hydrocarbons (NMHCs) in southern Taiwan. Ozone formation potentials (OFPs) of NMHCs were estimated using maximum incremental reactivity (MIR) and k_OH method (reactivity of NMHC with OH radical) to assess the relative effects of hydrocarbons on ozone formation. The measurements showed that mixing ratios of toluene, ethene, ethyne, ethane, isopantane and propane were the highest among all measured species at most of the sampling sites. Nevertheless, considering both the photochemical reactivities and mixing ratios of all the measured species, toluene, xylene, ethene and propene were calculated to have the highest OFPs and reactivities. The OFPs and reactivities assessed by the MIR and k_OH methods for the four compounds accounted for 54.5% and 39.3% of all the measured species. Larger benefit margin of ozone abatement may be obtained by reducing emissions of a group of key species with high OFPs.2,2-dimethylbutane (22DMC4) was used as an indicator of traffic emissions to distinguish traffic from non-traffic contributions of key species in Kaohsiung metropolitan area. It revealed that the contribution of non-traffic source was significant for toluene, whereas xylene was found to be primarily from the traffic source in Kaohsiung metropolitan area during the sampling periods.     

Weekday/Weekend Differences in OH Reactivity with VOCs and CO in Baltimore,Maryland

ABSTRACT

This study compared the first-order frequencies for OH associated with volatile organic compounds (VOCs) and CO (hereafter called OH reactivity with VOCs or CO), the product of the VOC or CO concentration, and their respective k_OH value, on an average weekday with that on an average weekend day at a core urban site in Baltimore, MD. The average daytime concentrations were calculated for each of the 55 available Photochemical Assessment Monitoring Station (PAMS) VOCs using data from the Baltimore site. The data were sorted in descending order to highlight the important species based on concentration. The OH reactivity with VOCs was sorted in descending order to identify the important species based on the magnitude of the OH reactivity. A similar process was followed for the OH reactivity with CO. The contribution of the significant species to the weekday/weekend difference in OH reactivity was examined.

The OH reactivity with C₅H₈ was the largest among the OH reactivity with the PAMS' VOCs and was the same on the weekday and weekend. The weekday/weekend difference in OH reactivity with VOCs was entirely due to differences in concentrations of the anthropogenic VOCs. The OH reactivity with VOCs was 11% larger on the weekday. When OH reactivity with CO was included, the OH reactivity was 13% larger on the weekday.     

Methane and carbon dioxide emissions from closed landfill in Taiwan

The atmospheric concentrations and emission rates of CH(4) and CO(2) were studied at three sites of the Fu-Der-Kan closed landfill and after as the multi-use recreational park in northern Taiwan. Atmospheric CH(4) and CO(2) concentrations of closed landfill were 1.7-4.6 and 324-409ppm, respectively. CH(4) and CO(2) emission rates ranged from 8.8 to 163mg m(-2)h(-1) and from 495 to 1531mg m(-2)h(-1), respectively. Diurnal variation was noted with higher values at night than those in daytime. After creation of the park, atmospheric CH(4) and CO(2) concentrations were 1.8-3.1 and 332-441ppm, respectively. CH(4) and CO(2) emission rates ranged from -1.1 to 2.3mg m(-2)h(-1) and from -135 to 301mg m(-2)h(-1), respectively. There were no notable diurnal variations in either atmospheric concentrations or emission rates.     

Validation of Mobile Source Emission Estimates Using Mass Balance Techniques

Air quality models must consider error in the emissions estimates as well as in the model itself. Currently, the accepted method for determining emission factors for mobile sources is through the use of the EPA model MOBILE₃. In this paper, emission factor calculations from a technique based on the conservation of mass are presented from experimental data. These emission factors are then compared to MOBILE₃ simulations using the experimental conditions and two different methods of obtaining the vehicle scenario. In both cases, the mass balance gave emission factors that were from 1.5 to 2.2 times those predicted by MOBILE₃. Next, mass balance and MOBILE₃ emission factors were used in the dispersion models CALINE3 and TXLINE in an effort to predict the observed CO concentrations. In both models, enhanced performance was observed when mass balance data were implemented.     

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.     

Sensitivity analysis and evaluation of MicroFacPM: a microscale motor vehicle emission factor model for particulate matter emissions

A microscale emission factor model (MicroFacPM) for predicting real-time site-specific motor vehicle particulate matter emissions was presented in the companion paper titled "Development of a Microscale Emission Factor Model for Particulate Matter (MicroFacPM) for Predicting Real-Time Motor Vehicle Emissions". The emission rates discussed are in mass per unit distance with the model providing estimates of fine particulate matter (PM2.5) and coarse particulate matter. This paper complements the companion paper by presenting a sensitivity analysis of the model to input variables and evaluation model outputs using data from limited field studies. The sensitivity analysis has shown that MicroFacPM emission estimates are very sensitive to vehicle fleet composition, speed, and the percentage of high-emitting vehicles. The vehicle fleet composition can affect fleet emission rates from 8 mg/mi to 1215 mg/mi; an increase of 5% in the smoking (high-emitting) current average U.S. light-duty vehicle fleet (compared with 0%) increased PM2.5 emission rates by -272% for 2000; and for the current U.S. fleet, PM2.5 emission rates are reduced by a factor of -0.64 for speeds >50 miles per hour (mph) relative to a speed of 10 mph. MicroFacPM can also be applied to examine the contribution of emission rates per vehicle class, model year, and sources of PM. The model evaluation is presented for the Tuscarora Mountain Tunnel, Pennsylvania Turnpike, PA, and some limited evaluations at two locations: Sepulveda Tunnel, Los Angeles, CA, and Van Nuys Tunnel, Van Nuys, CA. In general, the performance of MicroFacPM has shown very encouraging results.