PM-10 Exhaust Samples Collected during IM-240 ... - ACS Publications

Environ. Sci. Technol. 1997, 31, 75-83

PM-10 Exhaust Samples Collected during IM-240 Dynamometer Tests of In-Service Vehicles in Nevada JOHN C. SAGEBIEL,* BARBARA ZIELINSKA, PATRICIA A. WALSH, AND JUDITH C. CHOW Desert Research Institute, EEEC, P.O. Box 60220, Reno, Nevada 89506-0220 STEVEN H. CADLE AND PATRICIA A. MULAWA General Motors Research and Development Center, 30500 Mound Road, P.O. Box 9055, Warren, Michigan 48090-9055 KENNETH T. KNAPP AND ROY B. ZWEIDINGER U.S. EPA Mobile Source Emissions Branch, Mail Drop 48, Research Triangle Park, North Carolina 27711 RICHARD SNOW ManTech Environmental Technology, P.O. Box 12313, Research Triangle Park, North Carolina 27709

Twenty-three vehicles that were recruited by remote sensing and roadside inspection and maintenance (I/M) checks during the 1994 Clark and Washoe Remote Sensing Study (CAWRSS) were tested on the IM240 cycle using a transportable dynamometer. Six of these vehicles emitted visible smoke. Total gas-phase hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) exhaust concentrations were continuously measured in the diluted exhaust stream from the constant volume sampler (CVS) during IM240 testing. Two isokinetic PM-10 samples were collected simultaneously using cyclones and filter holders connected to a dilution tube. Teflon filters were collected for total mass and then extracted for chloride, nitrate, and sulfate ions. Quartz filters were analyzed by the thermal/ optical reflectance method for organic and elemental carbon. The quartz filters and backup vapor traps were then extracted and analyzed by GC/MS for 28 separate polynuclear aromatic hydrocarbons. Mass emission rates of PM-10 per vehicle ranged from 5.6 to over 1300 mg/mi, with most of the mass attributable to carbon. Except for one vehicle with high sulfate emissions, the ion emissions were relatively low. Total PAH emissions were in the range of 10-200 mg/mi.

of September 1994, the U.S. Environmental Protection Agency reported that 83 areas remained out of compliance with this standard (1). Recently, there has been increased interest in the basis of the PM-10 standard. This interest is due, in part, to epidemiological studies that report an association between ambient particulate matter with an aerodynamic diameter of 2.5 µm or less (PM-2.5) and excess mortality and morbidity in several cities (2). The U.S. EPA is under court order to complete a revision of the particulate matter criteria document by May 1996 and to establish a new ambient air quality standard by June 1997. Consideration will be given to basing the standard on PM-2.5 or smaller particles. The majority of direct particle emissions from many combustion sources, including gasoline- and diesel-powered motor vehicles, are in the size range less than 2.5 µm, which means these sources may become more important as this size range comes under closer scrutiny. A variety of sources contribute to the atmospheric PM-10 burden. On a national basis, the U.S. EPA estimates that the largest contributor to primary particles is fugitive dust (89%). All highway vehicles are estimated to account for only 3% of the total. However, the relative source contributions vary considerably between areas, which the U.S. EPA classifies as being dominated by either stationary sources, wood smoke, fugitive dust, or multiple sources (1). If the regulated particle size is changed, the relative contribution of various sources will change. The primary particle contribution of on-road mobile sources can be placed into several categories; fugitive dust emissions (also known as resuspended road dust); heavyduty vehicle exhaust emissions (largely from diesel engines); light-duty vehicle exhaust emissions (largely gasoline internal combustion engines); and tire, brake, and clutch wear emissions. This paper will consider only exhaust emissions from light-duty gasoline in-use vehicles. Particle emission rates from light-duty gasoline vehicles have decreased dramatically over the years. Vehicles manufactured before 1975 emitted between 150 and 250 mg/mi total particles when operated on the leaded gasoline available at that time (3). Use of unleaded gasoline in such vehicles resulted in a reduction of particulate emissions to about 25 mg/mi. Some early oxidation catalyst cars equipped with air pumps showed sulfate emission rates as high as 20 mg/mi. However, emission rates of total particles were below 10 mg/ mi for most production catalyst vehicles. Diesel vehicles, which were popular in the late 1970s and early 1980s had emission rates as high as 800 mg/mi. New light-duty cars and trucks must meet a particulate standard of 80 and 130 mg/mi, respectively. This standard is set primarily for diesel engines, which remain relatively few in number. Recent data (4) continue to show that properly functioning catalyst vehicles have particle emission rates below 10 mg/mi.

The national primary ambient air quality standards for particulate matter are (a) 150 µg/m3 over a 24-h period with no more than one expected exceedance per year and (b) 50 µg/m3 annual arithmetic mean for particles with an aerodynamic diameter of 10 µm or less (PM-10). The secondary standards are currently equal to the primary standards. As

Particle emissions from the in-use light-duty gasoline fleet have been poorly characterized. One study (5) examined seven 1977-1983 catalyst-equipped in-use vehicles with an average odometer reading of 77 000 mi and found that their exhaust emission rate of PM-2 averaged 28.5 mg/mi. On the other hand, the Unocal scrap program measured PM-10 emissions from 31 vehicles purchased for scrap. These vehicles, whose age averaged 22 years in 1990, had average emissions of 1510 mg/mi, with one vehicle emitting at a rate of 16 800 mg/mi. It is clear that a larger data base on particle emissions from in-use vehicles is needed before the impact of their emissions can be accurately determined.

* Corresponding author telephone: 702-677-3196; fax: 702-6773157; e-mail address: [email protected].

The objectives of this study were (a) to determine the practicality of making roadside dynamometer measurements of PM-10 emissions, (b) to start to assemble a database of

Introduction

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 1996 American Chemical Society

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particulate emission rates from on-road vehicles, (c) to conduct some chemical characterization of the particulate matter for source profile development, and (d) to correlate particle emission rates to the HC and CO emission rates. In this study, we sampled vehicles that had just come off the road, without making any changes to the vehicles that would affect emissions. By collecting samples during a loaded-mode dynamometer test (IM240), we have attempted to obtain samples that are representative of what these vehicles were emitting when on-road.

Experimental Section Two sites were used, one in Reno (westbound Kietzke Lane west of Galletti Way) and one in Las Vegas (northbound Eastern Avenue at Hadland Park). The sites were selected to provide a balance of a mix of old and new automobiles, hightraffic volume, and a convenient place to set up the roadside I/M checks and the dynamometer. The study was conducted in September 1994. Vehicle Selection and Testing. Vehicles were screened by infrared remote sensing, and high-emitting vehicles were pulled over and asked to volunteer for a roadside I/M test administered by the Nevada Department of Motor Vehicles (NDMV). The selection criterion varied at the different sites, but was generally greater than 4% CO or 0.3% HC as propane as measured by the remote sensor. However, if one of the IM test lanes was open and no vehicles meeting selection criteria were available, a vehicle would be pulled over at random. At all locations at least two remote sensors were operated in series, yet the vehicle had to meet selection criterion on only one sensor to be stopped. Additionally, at the Reno site only, a spotter was placed up-road from the remote sensors to identify visibly smoking vehicles, with the intention of pulling these vehicles for test regardless of the remote sensor reading. The spotter was not used at the other sites due to personnel limitations and because all smoking vehicles observed in Reno also failed on the remote sensors. The NDMV I/M test consists of low idle and 2500 rpm idle measurements of tailpipe CO and HC and visual inspections of emissions system components. The test must be passed annually by all 1968 and newer vehicles in Nevada for the vehicle to be registered. Approximately 370 vehicles were given this test during this study. If the driver was willing to let the vehicle be tested, the vehicle was inspected for safety and exhaust system compatibility with the dynamometer emission test equipment. The vehicle did not necessarily have to fail the idle IM test to be selected for IM240 testing. The only vehicle modifications made were to correct tire inflation. Vehicles were run through a warm-up cycle that involved a 2-min cruise at 50 mph prior to the IM240 test, which was then run in accordance with standard procedures. A subset of 23 vehicles was tested on the I/M 240 for PM-10. These vehicles were selected to include smoking vehicles, of which six were identified. Other vehicles were tested more of less at random, as conditions at the test facility allowed. Collection of PM-10 Samples. The U.S. EPA modified the CVS dilution tube to allow for PM-10 collection. This involved the addition of a downstream 90° radius section to the tube that allowed the insertion of two isokinetic sample probes into the straight section of the tube. Figure 1 is a schematic of the test apparatus. The sample probes were connected to PM-10 cyclones equipped with filter holders that were obtained from a commercial supplier (University Research Glassware, Carrboro, NC). The cyclones were operated simultaneously at a flow rate of 28.3 L/min using mass flow control. Flow was measured periodically with a dry gas meter. A 37 mm diameter Teflon filter (2.0 µm pore size Gelman Teflo) was used for the determination of mass and anions. A 37 mm diameter quartz filter (Pallflex Tissue

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FIGURE 1. Diagram of PM-10 sampling system installed in CVS dilution tunnel. Both cyclones were operated simultaneously at 28.3 L/min. Quartz 2500 QAT-UP) was used for the carbon analyses. The quartz filters were backed up by a vapor-phase trap for polynuclear aromatic hydrocarbons (PAH) consisting of 5 g of XAD-4 resin (polystyrene/divinylbenzene polymer) sandwiched between two polyurethane foam plugs (PUF). Two field blanks were collected, one each at the Reno and Las Vegas sites, by capping off the vehicle exhaust input port and running the CVS 4 min to simulate an IM240 test. For comparison to the sample filters, the blank values are reported in milligrams per mile, determined by assuming the dilution factor for the average vehicle run. No duplicate samples were collected, and no replicate IM240 tests were run on any vehicle. In addition, five dynamic media blanks (filters that were sent into the field and returned without being used) were analyzed. Sample Handling. Filter holders were loaded prior to use and stored on-site in a refrigerator (temperature ca. 4 °C). Following sampling, filters were returned to their plastic Petri dish holders and stored in the refrigerator. Transport back to the laboratory was in a cooler with blue ice packs, and laboratory storage was in a freezer at -10 °C (quartz filters) or the weighing room (Teflon filters). Analysis. All analyses were performed by Desert Research Institute’s laboratories using standard methods (6, 7). Prior to sampling, Teflon filters were stored at least 1 month in a controlled environment and at least 1 week in the weighing environment to stabilize the masses. After sampling, Teflon filters were equilibrated at least 24 h in the weighing environment (30% RH and 20 °C) prior to weighing for mass. Following acceptable mass measurements (replicate weighings within (10 µg), the Teflon filters were extracted, and the extracts were analyzed by ion chromatography for nitrate, sulfate, and chloride ions. Quartz-fiber filters were pre-fired for 3 h at 900 °C, with one filter from each batch tested to ensure that blank levels were below 1 µg/cm2 total carbon. After sampling, quartz filters had a 0.512 cm2 punch removed that was subjected to the thermal/optical reflectance (TOR) method for organic and elemental carbon (6). The TOR analysis reports the values for “organic carbon” and “elemental carbon”, which are defined, respectively, as the carbon that evolves in a pure helium atmosphere and that which requires the addition of 2% oxygen to remove. The values for organic and elemental carbon are corrected for charring by optical monitoring of reflectance. The lower quantitation limits for a sample collected during an IM240 test were 2.0, 0.86, and 0.34 mg/mi for mass, organic carbon,

TABLE 1. Summary of Vehicles Tested and Emissionsa IM240 emision rate (g/mi)

b

vehicle no.

model year

make

model

odometerb

HC

CO

NOx

field notes

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

1990 1989 1989 1989 1988 1988 1986 1985 1984 1984 1983 1983 1982 1982 1982 1982 1982 1981 1981 1979 1979 1976 1976

Mercury Ford Yugo Isuzu Honda Nissan VW Chevrolet Toyota Chevrolet Ford Ford Ford Ford Ford Toyota Mazda Ford Olds Buick Ford Olds Mercury

Sable wagon Pony 2-door pickup CRX Si Sentra Cabriolet S-10 Blazer pickup Celebrity Ranger pickup Ranger pickup station wagon Escort Mustang pickup 626 F150 pickup Toronado Regal Mustang Cutlass 2-door sedan

55 144 49 573 44 590 125 084 75 190 101 029 63 437 10 405* 119 780 3 398* 107 643 138 111 110 203 82 939 24 602* 155 441 145 070 19 137* 90 045 16 896* 88 216 144 811 60 145*

0.05 0.14 2.63 4.42 2.17 1.42 1.31 2.63 2.12 0.60 7.87 4.57 3.12 3.69 6.41 4.47 2.12 11.04 2.29 1.84 10.10 2.37 3.65

1.76 8.46 40.08 78.90 13.79 36.84 57.34 58.80 26.23 27.52 46.01 69.44 22.17 34.92 62.80 78.96 30.11 117.45 35.11 38.05 92.02 18.24 40.73

0.44 0.18 0.24 0.66 1.33 1.25 1.74 1.22 6.11 0.14 1.44 1.09 2.12 2.19 1.31 1.41 1.96 0.26 3.01 0.07 2.00 5.87 3.53

possible cold start

99 783 105 222 98 617

3.52 6.18 2.59

45.03 63.47 38.52

1.72 1.57 1.78

visible black smoke

visible smoke visible smoke visible smoke visible smoke overheated visible smoke av of all vehicles av of smokers (n ) 6) av of non-smokers (n ) 17)

a Vehicles are ordered by model year. Averages are presented for all vehicles and for those that emitted visible smoke and those that did not. An asterisk (*) indicates that the odometer likely rolled over.

TABLE 2. Summary of Particle Emissionsa vehicle no.

mass

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

5.6 32.4 103.0 59.0 13.4 22.0 25.6 106.4 10.1 7.8 693.4 115.9 6.8 801.0 1341.8 131.8 14.3 145.8 10.0 30.1 221.4 7.2 306.1 1.0 -1.6 183.08 557.85 50.81

particulate phase (mg/mi) total carbon nitrate sulfate

chloride

% of mass identifiedb

field notes

6.9 9.7 88.4 57.5 13.4 24.4 28.1 94.8 15.7 12.2 485.0 87.8 9.9 492.8 1042.9 108.8 20.1 111.4 16.0

0.00 0.06 0.04 0.00 0.03 0.00 0.04 0.06 0.00 0.04 0.09 0.00 0.00 0.07 0.06 0.06 0.00 0.05 0.00

0.12 13.59 0.61 0.08 0.05 0.09 0.12 0.37 0.05 0.07 0.20 0.11 0.12 0.28 0.24 0.13 0.04 0.41 0.07

0.11 0.08 0.11 0.11 0.08 0.09 0.09 0.10 0.11 0.08 0.09 0.11 0.08 0.10 0.11 0.15 0.10 0.11 0.10

127 72 87 98 101 112 111 90 156 160 70 76 150 62 78 83 141 77 161

possible cold start

217.7

0.08

0.06

0.10

98

237.4 1.2 0.9

0.07 0.00 0.00

0.18 0.03 0.03

0.12 0.07 0.06

78 130 -62

visible smoke Reno blank Las Vegas blank

151.47 404.50 50.26

0.04 0.06 0.03

0.81 0.23 1.04

0.10 0.11 0.10

104 77 115

av of all vehicles av of smokers (n ) 6) av of non-smokers (n ) 17)

visible black smoke

visible smoke visible smoke visible smoke visible smoke overheated

a Last two entries are field blanks. Particle data are corrected for media blanks, but are not field blank corrected. carbon, nitrate, sulfate, and chloride divided by mass.

and elemental carbon, respectively. The lower quantitation limits for the anions nitrate, sulfate, and chloride under the same conditions were 0.006, 0.006, and 0.07 mg/mi, respectively.

b

Calculated as the sum of total

The vapor-phase PAH traps had deuterated internal standards added and then were extracted by Soxhlet extraction in dichloromethane for 8 h. Extracts were reduced by rotary evaporation to 1.0 mL and analyzed by GC/MS in selected


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FIGURE 2. Percent of the total organic carbon evolved at each temperature in the analysis. Each individual vehicle is shown along with the average of the smoking and of the non-smoking vehicles. There is considerable variation among the individual vehicles. For the averages, only the 250 °C and 450 °C fractions were significantly different between the smoking and non-smoking vehicles.

FIGURE 3. Percent of the total elemental carbon evolved at each temperature in the analysis. Each individual vehicle is shown along with the average of the smoking and non-smoking vehicles. There was no significant difference between the smoking and non-smoking vehicles and generally more variability than for the organic carbon in Figure 2. ion monitoring mode for 28 PAHs ranging from naphthalene to coronene. After TOR analysis, the quartz filters were similarly extracted and analyzed for the same PAH.

Results and Discussion Table 1 lists the vehicles tested in this study, in order of model year, along with the odometer readings, field notes, and the IM240 emission rates of the regulated gas-phase pollutants. The average vehicle age was 10.5 years. Odometer readings were obtained from all vehicles. It was judged that six of the vehicles probably had either faulty readings or that the mileage had exceeded the 100 000 limit of the odometer, i.e., the odometer had rolled over. The average odometer reading for the remaining 17 vehicles was 99 800 miles. Six of the vehicles emitted visible smoke. The average age of these vehicles was 13.8 years.

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The average HC, CO, and NOx IM240 emission rates for the entire fleet were 3.52, 45, and 1.72 g/mi, respectively. Only vehicle number one had a low emission rate, and it is suspected that this car was stopped after passing the remote sensors in a cold-start condition. The site in Reno where this vehicle was stopped is close enough to a large parking lot that this is likely. The HC and CO emission rates for the smoking vehicles were 6.2 and 63.5 g/mi, while those for the non-smoking vehicles were 2.6 and 38.5 g/mi, respectively. This difference was statistically significant at the 99% confidence level for HC, but not for CO (p ) 0.062). Only one vehicle in this study could be classified as a low emitter. Therefore, consideration should be given in future studies to include additional low emitters to define better their particle emission rates.

TABLE 3. Organic Carbon (OC) and Elemental Carbon (EC) Emissionsa emissions (mg/mi) vehicle no.

OC

EC

% OC

4 11 14 15 18 23 av

Smokers 33.6 436.5 470.2 985.7 61.1 224.4 368.6

23.9 48.5 22.6 57.2 50.2 13.0 35.9

58 90 95 95 55 95 91

1 2 3 5 6 7 8 9 10 12 13 16 17 19 21 av

Non-Smokers 4.4 8.5 66.8 11.0 8.5 21.9 53.9 13.0 10.4 72.6 7.7 92.2 14.6 13.6 170.9 38.0

2.5 1.2 21.6 2.4 15.9 6.2 40.9 2.8 1.8 15.2 2.3 16.6 5.5 2.4 46.8 12.3

63 88 76 82 35 78 57 82 85 83 77 85 73 85 79 76

Blanks 1.2 0.9

0.0 0.0

100 100

Reno blank Las Vegas blank

a Data are presented as emission rate and as the percent of the total carbon that is OC.

Based on the remote sensing results, approximately 10% of the vehicles passing either site met the selection criteria. Since no further systematic screening was performed, the vehicles in this study are likely representative of the highest emitting 10% of the vehicles in these areas; however, the small number of vehicles tested in this program precludes any clear conclusion on this issue. The mean percent CO reading for the subset of vehicles tested on the IM240 was not significantly different from that of the entire fleet at the Reno location, and although it was different in Las Vegas, this may have been because the driving mode by the remote sensors was very slow (ca. 10 mph) due to traffic control.

Particle Emission Rates. Table 2 presents the total particle emission rates as well as the emission rates for total carbon, nitrate, sulfate, and chloride. The data have been blank corrected using the media blanks; however, we chose not to subtract the field blanks from the field data since there were only two blanks collected. The field blank data are also presented in Table 2. Note that the mass correction based on these blanks would be only 1 mg/mi. No nitrate was detected in the blanks. However, the sulfate and chloride blanks were significant. Particle emission rates varied widely from a low of 5.6 mg/mi to a high of 1342 mg/mi. The average IM240 particle emission rate for the entire fleet was 183 mg/mi. Separating the fleet into non-smoking and smoking vehicles gave average particulate emission rates of 50.8 and 558 mg/mi, respectively. The difference between these emission rates was significant at the 99.9% level using a pooled t-test (p ) 0.00025). Additionally, some vehicles visually identified as not emitting visible smoke actually emitted more PM-10 than some that did emit visible smoke. These emission rates can be compared to emission rate standards and literature values. However, it should be noted that the standards and the cited literature values are for a Federal Test Procedure (FTP) certification test, not an IM240 test. For properly functioning vehicles, particulate emissions may be higher in the cold- and hot-start portions of the FTP test than in the hot stabilized portion represented by the IM240. Thus, the IM240 may underestimate these emission rates. A correlation between FTP and IM240 testing is needed for particle emissions. The average emissions of the nonsmoking vehicles are below the current standard of 80 mg/ mi (although this standard was set for diesel vehicles, it remains in effect for late model light-duty vehicles for 50 000 mi). The smoking vehicles, on the other hand, significantly exceed this standard. Furthermore, the four lowest emitting vehicles (numbers 1, 10, 13, and 22) have an average emission rate of 6.8 mg/mi, which is comparable to the recent literature values for a normal emitter at 5.8 mg/mi (4). Percent Recovery of Mass Emissions. Table 2 also contains the percent of the mass that was identified as total carbon plus the anions measured. The average for all vehicles was 104 ( 33%, with 115 ( 32% identified for the non-smoking vehicles and 77 ( 12% identified for the smoking vehicles, where the uncertainty represents 1 SD. The percent identified was highly variable, ranging from 70 to 161% with lower mass samples showing excess recovery and high mass samples tending to be lower than 100%. A correlation between percent recovery and mass was calculated to examine this trend. The

FIGURE 4. Comparison of PM-10 mass vs total carbon PM-10 emission rates for all vehicles in the study with the smoking and non-smoking vehicles identified by different symbols on the plot. Note that some non-smoking vehicles actually emitted more than some smoking vehicles; however, both types emit a similar fraction of mass as carbon.


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FIGURE 5. Comparison of PM-10 mass vs organic carbon PM-10 emission rates for all vehicles in the study with the smoking and non-smoking vehicles identified by different symbols on the plot. Similarly with Figure 4, some non-smoking vehicles actually emitted more than some smoking vehicles; however, both types emit a similar fraction of mass as organic carbon.

FIGURE 6. Comparison of PM-10 mass vs elemental carbon PM-10 emission rates for all vehicles in the study with the smoking and non-smoking vehicles identified by different symbols on the plot. The regression line is for non-smoking vehicles only and shows a reasonable trend that is not followed by all the smoking vehicles. correlation was weak (linear correlation coefficient, r ) -0.52), but in the direction indicated. A variety of explanations were considered for the poor agreement between mass and total carbon on some of the lightly loaded filters. Analytical errors and errors in flow measurement cannot account for the differences. Flow in the sampling apparatus was controlled by calibrated mass flow controllers to minimize uncertainty. Quality assurance procedures and replicate analyses in the laboratory minimize the possibility of error there. The most likely explanation is that the deposits on the filters were not completely uniform. Since the entire Teflon filter is weighed, but only 7.5% (0.512 cm2 punch from a filter with a deposit area of 6.8 cm2) of the matching quartz filter is analyzed for carbon, the possibility exists that the punch is not representative of the “average” filter loading. Two filters (vehicles 7 and 8) were noted as having “reverse impaction” or a lighter colored center as compared to the outer rim. This strongly suggests that these had non-uniform deposits. Curiously, these two samples showed reasonably good (111 and 90%, respectively) recoveries. The configuration of the cyclones and filters leaves the possibility that the spinning current of air necessary for the proper operation of the cyclone was carried up to the filter without sufficient time to re-attain a uniform sample stream. The other possibility that cannot be entirely dismissed is

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random leaks in the sampling apparatus. Given the large variability in the mass identified, most of which is carbon, it is best to focus on the average recovery values and the details of the organic to elemental carbon splits, which should not be affected by inhomogeneous filter deposits. Carbon Emissions. Table 3 shows the emissions (in mg/ mi) for both organic carbon (OC) and elemental carbon (EC). The vehicles were split into smoking and non-smoking, and averages for the two groups are presented. For both OC and EC, the emissions from the smoking vehicles (369 and 35.9 mg/mi, respectively) exceeded those from the non-smoking vehicles (38 and 12.3 mg/mi, respectively). The differences were statistically significant at the 99% level (p ) 0.0015 for OC and p ) 0.005 for EC). However, the fraction of the emitted total carbon that was OC, 81% for the smoking vehicles and 75% for the non-smoking vehicles, was not significantly different between the two groups. It can be noted that the majority of the carbon is emitted as organic carbon (overall average was 77%); however, there are the exceptions, notably vehicle 6, which emitted only 35% of the carbon as organic carbon. For comparison, the carbon emission factors used by the PART5 model for calculating particle emissions from light-duty motor vehicles using unleaded gasoline range from a maximum of 30 mg/mi for noncatalyst vehicles to 4.3 mg/

FIGURE 7. Comparison of PM-10 mass and gas-phase hydrocarbons (HC) for all vehicles in the study with the smoking and non-smoking vehicles identified by different symbols on the plot. The regression line is for non-smoking vehicles only and shows a reasonable trend that is not followed by all the smoking vehicles.

FIGURE 8. Comparison of PM-10 mass and carbon monoxide (CO) for all vehicles in the study with the smoking and non-smoking vehicles identified by different symbols on the plot. The regression line is for non-smoking vehicles only and shows a reasonable trend which is not followed by all the smoking vehicles. mi for 1981 and newer model year catalyst-equipped vehicles (8). Figures 2 and 3 give detail on the carbon emissions by presenting the OC and EC fractions as the percentage evolved at the various temperatures in the analysis process. The two groups of vehicles were significantly different in only the 250 and 450 °C OC fractions, which were significantly different at the 99% level (p ) 0.0033 for 250 °C OC and p ) 0.0008 for 450 °C OC). The variability among these proportions suggest that identifying a source, such as motor vehicles, based on these separations would be subject to considerable error. For this reason, we feel that the addition of the gas- and particlephase PAH species in a source profile for motor vehicles will help reduce the uncertainty in any source apportionment conducted with those profiles. The emissions of total carbon are strongly correlated with mass (r ) 0.993), as shown in Figure 4. In this and the following figures, the smoking vehicles are identified by different symbols. The strong correlation was expected since total carbon accounted for an average of 104% of the mass. As stated earlier, the smoking vehicles as a group emit more of both total carbon and mass than those that did not emit visible smoke. The situation is very similar for mass and

organic carbon (r ) 0.993), as shown in Figure 5. Again, this is expected since 77% of the total carbon was emitted as OC, on average. Figure 6 shows the plot of mass vs elemental carbon, which has a poorer correlation (r ) 0.655). Note that the maximum EC emission rate is 57 mg/mi as opposed to 986 mg/mi for organic carbon. The correlation improves to r ) 0.87 if only the non-smoking vehicles are included. The regression line in Figure 6 is for the non-smoking vehicles only. Ion Emissions. The majority of the vehicles had very low emission rates of the measured anions (Table 2). The one exception is a single vehicle (no. 2) that had emissions of over 13 mg/mi sulfate in the exhaust, which is 42% of the total mass emissions from this vehicle. The sulfur content of the fuels, which averaged 0.011 wt % in Reno and 0.019 wt % in Las Vegas, were not sufficient to produce this level of direct sulfate emisstion. Thus, we suspect this material may have built up over time and was dislodged during the test. Laboratory confirmation showed the value was valid, and it is an important part of the mass balance for this vehicle, thus we feel the value is correct. The next highest sulfate emitter was vehicle 3 at 0.61 mg/mi. Excluding these two vehicles, the average sulfate emission was 0.12 mg/mi. Nitrate


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TABLE 4. Summary of Polynuclear Aromatics (PAH) Emissionsa sum of PAH emissionsb (mg/mi)

selected total PAH emissions (mg/mi)

vehicle no.

PM10 (mg/mi)

filter

PUF

total

naphthalene

pyrene

B(a)P

coronene

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

5.6 32.4 103.0 59.0 13.4 22.0 25.6 106.4 10.1 7.8 693.4 115.9 6.8 801.0 1341.8 131.8 14.3 145.8 10.0 30.1 221.4 7.2 306.1

0.13 0.22 0.49 0.99 0.10 0.10 0.48 0.88 0.14 0.16 6.55 1.84 0.08 1.65 19.59 0.94 0.08 3.11 0.08 0.00 4.75 0.00 1.06

9.33 19.55 36.55 107.86 55.89 38.63 49.15 18.25 58.07 18.26 135.55 91.39 77.12 117.27 180.85 101.70 41.71 174.26 45.39 49.49 171.47 53.71 94.88

9.46 19.77 37.04 108.85 55.99 38.73 49.64 19.13 58.21 18.42 142.10 93.22 77.19 118.92 200.44 102.64 41.79 177.37 45.47 49.49 176.22 53.71 95.95

7.88 18.17 16.38 54.68 24.17 24.99 26.83 3.39 34.78 15.06 59.86 43.69 50.71 54.96 79.96 49.67 15.17 86.25 17.42 28.85 77.37 30.49 33.03

0.04 0.02 0.26 0.32 0.03 0.13 0.21 0.24 0.05 0.12 1.75 0.89 0.05 0.28 3.01 0.52 0.14 1.13 0.04 0.06 1.47 0.17 0.26

0.00 0.00 0.01 0.03 0.00 0.00 0.03 0.05 0.00 0.01 0.36 0.05 0.00 0.03 0.90 0.03 0.00 0.23 0.00 0.00 0.13 0.01 0.06

0.00 0.01 0.02 0.04 0.00 0.00 0.04 0.02 0.00 0.01 0.76 0.14 0.00 0.02 1.93 0.06 0.00 0.28 0.00 0.00 0.22 0.00 0.05

visible smoke

1.89 5.49 0.62

75.93 135.11 55.04

77.82 140.61 55.65

37.12 61.46 28.53

0.49 1.12 0.26

0.08 0.27 0.02

0.16 0.51 0.03

av of all vehicles av of smokers (n ) 6) av of non-smokers (n ) 17)

183.08 557.85 50.81

field notes possible cold start visible black smoke

visible smoke visible smoke visible smoke visible smoke overheated

a PAH data are corrected for media blanks and field blanks. b Sum of 28 PAH species quantitated from filters and backup cartridges. Values are blank subtracted, thus no blank values are given.

TABLE 5. Average PAH Emission Ratesa compound

non-smoker (mg/mi)

smoker (mg/mi)

ratio smoker/non

low PM-10 (mg/mi)

high PM-10 (mg/mi)

ratio high/low

naphthalene 2-methylnaphthalene 1-methylnaphthalene sum of dimethylnaphthalenes biphenyl acenaphthylene acenaphthene fluorene phenanthrene anthracene fluoranthene pyrene retene benzonaphthothiophene benz[a]anthracene chrysene benzo[b+j+k]fluoranthene benzo[e]pyrene benzo[a]pyrene indeno[1,2,3-cd]pyrene dibenzo[ah+ac]anthracene benzo[b]chrysene benzo[ghi]perylene coronene

28.51 13.97 5.86 4.33 0.43 1.21 0.08 0.30 0.47 0.12 0.22 0.27 0.00 0.0004 0.037 0.022 0.040 0.022 0.020 0.013 0.002 0.002 0.065 0.034

61.46 38.19 16.33 13.67 0.76 3.11 0.23 0.86 1.11 0.37 0.88 1.12 0.04 0.0037 0.30 0.17 0.28 0.18 0.27 0.15 0.02 0.02 0.57 0.51

2.2 2.7 2.8 3.2 1.8 2.6 3.0 2.9 2.3 3.0 4.1 4.1

24.54 9.92 4.13 3.04 0.31 0.44 0.02 0.15 0.26 0.068 0.090 0.089 0.000 0.0005 0.015 0.009 0.028 0.010 0.005 0.005 0.001 0.000 0.018 0.006

61.04 39.83 17.61 14.93 0.76 3.97 0.35 1.14 1.34 0.48 1.04 1.35 0.05 0.00 0.35 0.19 0.31 0.20 0.30 0.17 0.02 0.02 0.67 0.60

2.5 4.0 4.3 4.9 2.5 8.9 16 7.8 5.2 7.0 12 15

10 8.1 7.4 7.1 8.4 13 11 9.3 6.5 8.8 15

9.2 24 21 11 20 56 36 17 37 100

a Averages are presented for smoking and non-smoking vehicles as well as the ratio of smoker/non-smoker. Low PM-10 is the average for vehicles with less and 50 mg/mi, and high PM-10 is vehicles over 150 mg/mi. All data are for total PAH.

emissions were generally quite low; however, the average smoking vehicle emitted at twice the rate (0.06 mg/mi) of the average non-smoking vehicle, a difference that was statistically significant at the 95% level (p ) 0.045). Previous work (4) reported emissions of 16-29 µg/mi for nitrate and 90-170 µg/mi for sulfate. With the exception of the high sulfate emitters, these data are comparable, with average nitrate emissions of 30 µg/mi and average sulfate emissions (omitting the two high values) of 120 µg/mi. Note that the field blanks

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showed no nitrate but did have an average of 30 µg/mi sulfate. Chloride emissions showed the least variability among the emissions (RSD ) 18%), but had a fairly high field blank value and are thus suspect. Future work should continue to focus on the measurement of organic and elemental carbon, while there appears to be little need to measure the anions. Comparison of Gas-Phase and Particle Emissions. The EPA Motor Vehicle-Related Air Toxics Study (9) noted that particle emissions tend to increase as total gas-phase

hydrocarbons increase. Since there were insufficient data on particle emission rates to characterize in-use vehicles, the results from one study were used to derive the estimate that particulate matter is 1.1% of the mass of total hydrocarbon emitted on an FTP. The results of the present study were examined for a similar trend. The particulate emission rate was correlated to both HC and CO. CO was included since it is a strong indicator of rich operation. The correlation coefficients were 0.446 for HC and 0.200 for CO. Figure 7 shows mass vs HC, and Figure 8 shows mass vs CO for all vehicles tested. The correlations were improved if only the non-smoking vehicles were considered (r ) 0.849 for HC and r ) 0.859 for CO). On average, the non-smoking vehicle particle emission rate was 2.0% of the HC emission rate, while that of the smoking vehicles was 9.0% of the HC emission rate. The slope of the linear regression between particle and HC emission rates indicates that the particle mass is 3.1% of the HC mass for the non-smoking vehicles. While this rate is higher than that derived by the EPA for FTP emissions, the lack of data comparing the IM240 to the FTP prevents any conclusions from being drawn regarding actual differences. Overall, the data suggest that the mechanisms of particle formation are different between the non-smoking and the highest emitting smoking vehicles. Since no diagnostics were performed on these vehicles, the cause of the differences is unknown. However, it is probable that one difference is combustion of oil. The significance of this is that for certain smoking vehicles the CO and HC emission rates are independent of the total PM-10 mass emission rate. This is important in that the worst (smoking) PM-10 emitters cannot be fully accounted for on the basis of their CO or HC emissions. PAH Emissions. Table 4 summarizes the PAH emissions from the tested vehicles. Also on this table for comparison is the total PM-10 emission rate (in mg/mi). These emission are similar to those reported by Siegl et al. (4) for both a normal and high-emitting vehicle. The filter-associated PAH are presented separately from the total so that they can be compared directly with the PM-10 emission rate. The PAH found on the PUF backup cartridge existed primarily in the gas phase; however, these data may not be indicative of the atmospheric distribution of these compounds due to the possibility of artifact formation (10). For this reason, the total (gas plus particle phase) PAH is a more useful value for looking at these source samples and should also be used in ambient sample collection. The average smoking vehicle produced more PAH emissions than the average non-smoking vehicle, and this difference was statistically significant with greater than 95% confidence. The correlation between total PAH emissions and PM-10 emissions was 0.683, and 0.704 between total PAH and total carbon emissions. However, the correlation between filter-associated PAH and PM-10 total carbon was 0.918 and between filter PAH and PM-10 mass was 0.874. It is reasonable that the correlation between the filter PAH and mass is better than between total PAH and mass since the total contains a large fraction of gas-phase compounds. Table 5 directly compares the emissions of each PAH from the smoking and non-smoking vehicles. The ratio of the smoking to non-smoking vehicle emission is also presented, and this ratio tends to increase with the higher molecular weight PAH. The low PM-10 column is the average for vehicles that emitted less than 50 mg/mi PM-10, and the high PM-10 column is the average for vehicles emitting over 150 mg/mi. The high/low ratio increases even more dramatically than that for the smoking/non-smoking grouping, suggesting an alternate way of separating the vehicles.

While this study has demonstrated that field IM240 PM10 measurements can provide useful information about the particulate emissions of the in-use light-duty gasoline vehicle fleet, future work should also include emission test replicates and a larger number of field blanks to define better the accuracy and precision of the data. Efforts will be made to improve the uniformity of deposits on filters in hopes of eliminating the problems in determining the amount of carbon in the samples. Determination of the significance of the smoking vehicles will require an estimate of their frequency in the current in-use vehicle population. Particle emission rates from a larger population of in-use normal and high emitter vehicles will be required before a reasonable assessment can be made regarding their contribution to the particle inventory. Inventory estimates will also require the correlation of the IM240 particle emission rates to those from the FTP and other driving cycles and a determination of the impact of factors such as ambient temperature.

Acknowledgments Funding for this work was provided by General Motors Research and Development Center. Financial support for the overall project (CAWRSS) came from the State of Nevada, I/M Review program. The U.S. EPA Mobile Source Emissions Branch provided the dynamometer for this study. The information in this document has been funded wholly or in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Literature Cited (1) U.S. Environmental Protection Agency. National Air Quality and Emissions Trends Report, 1993 EPA-454/R-94-026; U.S. EPA: Washington, DC, 1994. (2) Dockery, D. W.; Pope, C. A., III. Annu. Rev. Pub. Health 1994, 15, 107-132. (3) Cadle, S. H.; Nebel, G. J.; Williams, R. L. SAE Transactions 1979, 87, 2381. (4) Siegl, W. O.; Zinbo, M.; Korniski, T. J.; Richert, J. F. O.; Chladek, E.; Paputa Peck, M. C.; Weir, J. E.; Schuetzle, D.; Jensen, T. E. SAE Pap. 1994, No. 940581. (5) Hildemann, L. M.; Markowski, G. R.; Cass, G. R. Environ. Sci. Technol. 1991, 25, 744-759. (6) Chow, J. C.; Watson, J. G.; Pritchett, L. C.; Pierson, W. R.; Frazier, C. A.; Purcell, R. G. Atmos. Environ. 1993, 27A, 1185-1201. (7) Chow, J. C.; Watson, J. G. Guidelines for PM-10 Sampling and Analysis Applicable to Receptor Modeling; U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards: Washington, DC, 1994; EPA-452/R-94-009. (8) U.S. Environmental Protection Agency, Office of Mobile Sources National Motor Vehicle and Fuels Emission Laboratory. Draft User’s Guide to PART5: A program for calculating particle emission from motor vehicles; Report No. EPA-AA-AQAB-94-2; U.S. EPA: Washington, DC, 1995. (9) U.S. Environmental Protection Agency, Office of Mobile Sources Emissions Planning and Strategies Division. Motor VehicleRelated Air Toxics Study; EPA 420-R-93-005; U.S. EPA: Washington, DC, 1993. (10) Coutant, R. W.; Brown, L.; Chuang, J. C.; Riggin, R. M.; Lewis, R. G. Atmos. Environ. 1988, 22, 403-409.

Received for review February 14, 1996. Revised manuscript received September 9, 1996. Accepted September 9, 1996.X ES960137I X

Abstract published in Advance ACS Abstracts, November 15, 1996.


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PM-10 Exhaust Samples Collected during IM-240 ... - ACS Publications

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