Pollutant Constituents of Exhaust Emitted from Light-Duty Diesel 1 Vehicles 2 3 4 5 6 7 8 By 9 10 11
Chiang Hung-Lung*, Lai Yen-Ming, and Chang Sheng-You 12 13 14 15 16 17 18 19 20 21 22
*To whom correspondence should be addressed; 23
E-mail:hlchiang@mail.cmu.edu.tw; Tel: 886-4-22079685; Fax: 24
886-4-22079687 25
Pollutant Constituents of Exhaust Emitted from the Light-Duty Diesel 27
Vehicles 28
Chiang Hung-Lung, Lai Yen-Ming, Chang Sheng-You 29
30
Department of Health Risk Management, China Medical University, Taichung, 31 40402, Taiwan 32 33 ABSTRACT 34
Light-duty diesel exhaust particulate matter and its constituents, including 35
elemental carbon, organic carbon, water-soluble ionic species, elements, and 36
polyaromatic hydrocarbons (PAHs), were measured by a dynamometer study 37
and following the driving pattern of federal test procedure-75 (FTP-75). Fuel 38
consumption of these light-duty diesel vehicles was in the range of 39
0.106-0.132 l km-1, and the average emission factors of NMHC (non-methane 40
hydrocarbon), CO and NOx for light-duty vehicles were 0.158 (92% of total 41
hydrocarbon), 1.395, and 1.735 g km-1, respectively. The particulate emission 42
factor of light-duty diesel vehicles was 0.172 g km-1, and PM2.5 contributed to
43
88% of particulate mass. Al, S, Ca, and Fe emission factors were about 44
0.83-1.24 mg km-1 for PM2.5, and the particulate mass fractions of these
45
elements ranged from 66-90% in PM2.5. Nitrate, sulfate, ammonium and nitrite
46
were the major ionic species in diesel PM, and their emission factor ranged 47
from 0.22-0.82 mg km-1 for PM2.5. The emission factor of total PAHs was 3.62
48
mg km-1 in this study, with about 40% in the gas phase and 60% in the 49
particulate phase. Acenaphylene, naphthalene, fluoranthene, pyrene, and 50
anthracene were the dominant PAHs, and their emission factors were more 51
than 0.19 mg km-1. The content of nitro-PAHs was low, with most less than 52
0.040 mg km-1. 53
Keywords: diesel exhaust, particulate composition, emission factor, 54
1. INTRODUCTION 55
Chemical constituents are an important issue in the study of diesel 56
exhaust emission. Exposure to air pollutants increases the risk of 57
cardiovascular disease. Numerous epidemiological studies have shown that 58
an increase in adverse cardio-pulmonary effects is associated with an increase 59
in particulate matter level (HEI, 2003; Pope et al., 2004). Recent studies have 60
revealed that diesel exhaust particles could induce inflammation in cytokines 61
(Mazzarella et al, 2007), cytokine/chemokine response (Ø vrevik et al, 2010), 62
cellular oxidative stress (Suzuki et al, 2008), mutation yield in human-hamster 63
hybrid cells (Bao et al, 2007) etc. Diesel exhaust particles have been identified 64
as a class 2A human carcinogen (International Agency for Research on Cancer, 65
IARC) and related to an increase in the incidence of respiratory allergy, 66
cardiopulmonary morbidity and mortality, and risk of lung cancer (Kizu et al., 67
2003). 68
Generally, diesel vehicles contribute only a small fraction of particulate 69
matter (0.25-1.4% of PM2.5) in the atmosphere (Hwang and Hopke, 2007;
70
López-Veneroni, 2009), but most people are concerned with the health effects 71
of diesel exhaust particles (Alföldy et al, 2009). Therefore, elucidating the 72
chemical constituents of diesel exhaust is important to understand their toxicity 73
(Lin et al., 2008a; Lin et al., 2008b; Schneider et al., 2008; Cheng et al., 2010). 74
In addition, diesel fuel characteristics (i.e., sulfur content, fuel density, 75
distillation point, cetane index) and engine operation conditions (power loading, 76
exhaust temperature, engine speed, air/fuel ratio exhaust gas circulation) 77
could affect the exhaust compositions and particulate size distribution (Lim et 78
al., 2007; Lapuerta et al., 2007; Chung et al., 2008, Zhu et al., 2010). Most 79
studies in the literature have investigated the constituents of diesel exhaust 80
particles including carbon content (organic carbon and elemental carbon), 81
metal, inorganic ions, polyaromatic hydrocarbons, etc. (Kawanaka et al., 2007; 82
Maricq, 2007; Fushimi et al., 2008; Lin et al., 2008a; Cheng et al., 2010). Few 83
studies have investigated the comprehensive chemical constituents of diesel 84
exhaust particulate matter in detail. Typical mass fraction of diesel particle was 85
mainly in accumulation mode, 0.050 m < Dp < 1.0 m, with a maximum 86
concentration between 0.1 and 0.2 m and small mass peak in nuclei mode 87
and coarse mode (Kittelson, 1998; Kittelson, 2002). Significant and 88
fundamental changes have been made to the diesel engine combustion 89
process and associated after-treatment technologies (i.e., catalyst, diesel 90
particle filter, SCR catalyst) to meet stringent regulations and reduce emissions 91
of NOx and particulate matter (Biswas et al., 2008). However, diesel vehicles 92
are still a concern with regard to their pollution emission and health effects. 93
In general, two methods are used to measure vehicle emissions: the 94
dynamometer test and real-world study (i.e., roadside and tunnel studies). The 95
emission factors of specific engines can be determined by a dynamometer; 96
measurements from individual cars are still the standard in dynamometer 97
studies for many countries (Heeb et al., 2000, 2002, 2003; Nelson et al., 2008; 98
Oanh et al., 2010). 99
Actual traffic emission data have been obtained from roadsides or road 100
tunnels (De Vlieger, 1996; Lenaers, 1996; Pierson et al., 1996; Laschober et 101
al., 2004; Stemmler et al., 2005; He et al., 2008); the emission factor has been 102
determined by a mathematical method that does not reflect actual vehicle 103
emissions. Because dynamometer testing is a standard method and 104
determines tailpipe exhaust emission, it was selected in this work. 105
Detailed chemical constituents provide baseline information to 106
determine the effects of diesel vehicle exhaust. Many studies have focused on 107
diesel exhaust emission and composition using a dynamometer. However, 108
detailed information about PM concentration and composition is still necessary 109
to compare different areas. In this study, PM2.5 and its compositions including
110
elemental carbon, organic carbon, water-soluble ionic species, elements, and 111
polyaromatic hydrocarbons were measured to determine their emission 112 factors. 113 114 2. EXPERIMENT 115
2.1 Light-duty diesel vehicles and testing driving pattern 116
Six in-use light-duty vehicles were selected on the basis of accumulated 117
mileage and produced year. All vehicles were without pollution control 118
equipment, mileage ranged from 56,000 to 160,000 km, and the displacement 119
volume ranged from 2184 to 2835 cc. Table 1 presents more detailed 120
information such as produced year, mileage, weight and engine capacity of all 121
selected vehicles. 122
All selected vehicles were tested on a chassis dynamometer following 123
test procedure FTP-75, which is used in Taiwan to certify new vehicles. The 124
dynamometer is located in a certified laboratory located in ARTC (Automotive 125
Research & Testing Center, Taiwan). All vehicles were visually examined for 126
safety prior to testing on the following day. The distance and average speed 127
of FTP-75 are 17.48 km and 34.1 km hr-1, respectively. 128
129
2.2 Criteria pollutant sampling and analysis 130
All exhaust samples were taken from a constant volume dilution 131
sampling system. The dilution system, designed to meet the specifications 132
covered in the U.S. Federal Register (1986), was connected to a constant 133
volume sampling system (Horiba, Japan) to dilute the exhaust flow rate to 9 m3 134
min-1. Exhaust samples, taken at the end of the entire cycle of the FTP, were 135
analyzed for CO, HC, NOx and CO2 by auto-monitors (HORIBA MEXA-9200).
136
The background concentrations of those pollutants were also analyzed 137
routinely and deducted from the test results. Background concentrations 138
were about 2 ppm for CO, 6 ppm C for HC, 0.1 ppm for NOx and 0.1% for CO2.
139
The analytical errors for CO, HC, NOx and CO2 were approximately
140 0.01-0.08%, 0.01-0.17%, 0.02-0.06% and 0.25-0.38%, respectively. 141 142 2.3 Particle sampling 143
A dilution tunnel and a monitoring system were installed downstream of 144
the diesel exhaust to supply air for dilution and to measure particles and gas 145
pollutants. A cascade impactor (Graseby Anderson Mark III) with quartz filters 146
(with diameters of 64 mm, Pallflex, Pall Corporation, USA) is installed 147
downstream of the dilution tunnel to collect size-resolved samples. These 148
impactors can effectively separate the particulate matter into eight size ranges 149
with the following equivalent cut-off diameters: 6.6-10.5 (stage 8), 4.4-6.6 150
(stage 7), 3.1-4.4 (stage 6), 1.9-3.1 (stage 5), 1.0-1.9 (stage 4), 0.6-1.0 (stage 151
3), 0.4-0.6 (stage 2), and <0.4 m (stage 1). A linear interpolation method was 152
employed to determine the mass concentration of PM2.5 and PM10. All quartz
153
filters were baked at 900oC for 3h before use to ensure low concentrations of 154
organic compounds on the blank filter materials. In addition, polyurethane 155
foam (PUF) and an XAD-16 resin backup cartridge were utilized to collect 156
PAHs in the vapor phase, which is connected after the particle sampling 157 system. 158 159 2.4 Chemical analysis 160 2.4.1 Water-soluble ions 161
One-eighth of the particle filter sample of each stage was ultrasonically 162
extracted for 2 h into 20 ml of deionized distilled water and passed through a 163
Teflon filter of 0.45 m nominal pore size. Ion chromatography (IC, Dionex, 120) 164
was used to analyze the concentration of anions (Br-, F-, Cl-, NO2-, NO3-, SO42-)
165
and cations (Na+, NH4+, K+, Mg2+, Ca2+). Anions were separated using an
166
IonPac AS 12A (4×200 mm) analytical column, an AG 14 guard column with a 167
10 l sample loop, and an anion self-regenerating suppressor-ultra. A solution 168
of 2.7 mM Na2CO3/0.3 mM NaHCO3 was used as an effluent at a flow rate of
169
1.5 ml min-1. Cations were separated using an IonPac CS 12A (4×250 mm) 170
analytical column and a CG 14 guard column, with a 50 l sample loop, and a 171
cation self-regenerating suppressor-ultra. A solution of 20 mM 172
methanesulfonic acid was used as the eluent at a flow rate of 1 ml min-1. The 173
recovery ranged from 87% (Na+) to 109%( F-). 174
2.4.2 Elemental constituents in particulate matter 175
The one-eighth particle filter samples were mixed with a 20 ml acid 176
mixture (HNO3:HClO4:HF = 5:3:2, v/v) in a Teflon-lined closed vessel and
177
placed in a high-pressure digestion oven at 170oC for 5h. The digested acid 178
mixture was analyzed to determine the trace elements. A Perkin Elmer 179
OPTIMA 3000 ICP-AES was used to determine the Al, Ca, Fe, K, Mg, Na, S, 180
Co and Zn concentrations. Additionally, a SCIEX Elan Model 5000 ICP-MS 181
manufactured by Perkin-Elmer was employed to determine As, Ba, Cd, Cr, Cu, 182
Mn, Ni, Pb, Sb, Se, Sr and V concentration. Blank and duplicate samples 183
were also analyzed in this study. 184
185
2.4.3 Organic and elemental carbon in particulate matters 186
Particulate samples intended for carbon analysis were collected on 187
quartz-fiber filters that had previously been heated in air at 900oC for 4h to 188
lower their carbon blank level. The particle filter sample was stored below 4oC 189
until analysis. Total carbon (TC) and elemental carbon (EC) were measured 190
with a C/H/N elemental analyzer (Carlo Erba EA 1110). The procedure 191
performed in this study to determine particle carbon content is similar to the 192
method described by Cachier et al. (1989). Samples one-eighth the amount 193
of each filter were heated in advance in a 340oC oven for 100 min to expel the 194
organic carbon (OC) content, then fed into the elemental analyzer to obtain the 195
EC content. Another one-eighth sample was fed directly into the elemental 196
analyzer without pre-treatment to obtain the TC concentration. EC could be 197
determined by the difference of TC and OC. However, the EC fraction as 198
measured by this method can be overestimated, so the use of thermo-optical 199
techniques is highly recommended by other studies (Turpin et al., 2000; 200
Schmid et al., 2001; Sillanpää et al., 2005). 201
202
2.4.4 Reference sample validation 203
To validate the analysis method, NIST Standard Reference Material SRM 204
1648 was used. About 10 mg of SRM 1648 and 1650a, which approximates 205
the composition of urban particulate matter and diesel particulate matter, 206
respectively, was used to examine the accuracy and reliability of the analysis 207
method. Al, As, Ba, Co, Cr, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, Se, Sr, 208
V, and Zn were recovered in the acceptable range (recovery: 82-108%). In 209
addition, the recovery of three water-soluble ionic species, F-, Cl-, and SO42-,
210
was 87-109%, which is in the acceptable range by the analysis method of ion 211
chromatography. 212
213
2.4.5 Polyaromatic hydrocarbons (PAHs) 214
The 16 PAH (polyaromatic hydrocarbons) and 10 nitro-PAH standards 215
(purity of >99%) including Naphthalene (NaP), Acenaphthylene (AcPy), 216
Acenaphthene (AcP), Fluorene (Flu), Phenanthrene (PA), Anthracene (Ant), 217
Fluoranthene (FL), Pyrene (Pyr), Benzo(a)anthracene (BaA), Chrysene (CHR), 218
Benzo(b)fluoranthene (BbF), Benzo (k)fluoranthene (BkF), Benzo(a)pyrene 219
(BaP), Indeno(1,2,3-cd)pyrene (IND), Dibenzo(a,h)anthracene (DBA) and 220
Benzo(g,h,i)perylene (BghiP); and 2-Nitrofluorene (2-nFlu), 9-Nitroanthracene 221
(9-nAnt), 3-Nitrofluoranthene (3-nFL), 1-Nitropyrene (1-nPyr), 222
7-Nitrobenzo(a)anthracene (7-nBaA), 6-Nitrochrysene (6-nCHR), 223
1,3-Dinitropyrene (1,3-DnPyr), 1,6-Dinitropyrene (1,6-DnPyr), 224
1,8-Dinitropyrene (1,8-DnPyr) and 6-Nitrobenzo(a)pyrene (6-nBaP), were 225
purchased from Supelco Inc. (USA). Dichloromethane, n-hexane, acetone, 226
acetonitrile, silica gel (0.063–0.200 mm, activated at 150°C for 18 h prior to 227
use), anhydrous sodium sulfate (baked at 400°C for 4 h prior to use) and other 228
reagents were pesticide analysis grade and/or residue analysis grade and 229
purchased from E. Merck, Germany. 230
231
2.4.5.1 Sample extraction and cleanup 232
Combination samples of polyurethane foam (PUF) and XAD-16 resin 233
were extracted using the Soxhlet extraction procedure in an all-glass Soxhlet 234
system combined with an electro-thermal heating plate. The samples were 235
extracted for 16 h with 300 ml of mixed solvent (dichloromethane-acetonitrile 236
3:1, by volume) in a 500-ml flat-bottom flask. The filters (cut size was larger 237
than 1.9 m) were mixed as one sample for consideration of low PAH content 238
in large particles to ensure that the concentration was higher than the method 239
detection limitation. Samples of quartz filter were extracted using sonication 240
with the above solvent three times (3×40=120 ml) for periods of 15 min. The 241
temperature of the sonication bath was maintained between 25 and 30°C. 242
The extracts from the various procedures were concentrated on a rotary 243
evaporator (EYELA, Japan) equipped with a water bath held at 40°C, and the 244
solution volume was reduced to 1-2 ml. In the cleanup process, the residual 245
solution was introduced into a silica column (1 cm internal diameter and 25 cm 246
length), and the column was first eluted with 10 ml of n-hexane. About 2 cm 247
height of anhydrous sodium sulfate was packed at the fore-end of the cleanup 248
column to exclude water. The n-hexane fraction was discarded, and the 249
available fractions were then obtained by elution with 20 ml of 250
dicloromethane-hexane 1:2 and then 30 ml of acetone-hexane 1:2. The 251
last two fraction s were comb ined and concentrated just to dryness, then 252
quantified to 2 ml (PUF+XAD-16) or 1 ml (quartz filter) with solvent 253
acetone-hexane 1:2. The final solutions were analyzed with the gas 254
chromatography (GC) method. 255
256
2.4.5.2. Gas chromatography method 257
PAHs were analyzed by GC-MS. The GC apparatus consisted of a 258
Hewlett-Packard GC 6890 equipped with a mass (5973 N) and split/splitless 259
injector. An HP-5MS capillary column (5% phenyl methyl siloxane, 30 m, 260
internal diameter 0.32 mm, and film thickness 0.25 µm) was used. The 261
injector program was set to 280°C at the pulsed splitless mode (12 psi for 1 262
min). The oven temperature program was 60°C for 1 min, 35°C min−1 to 170°C, 263
8°C min−1 to 210°C, 4°C min−1 to 300°C, and 15°C min−1 to 320, which was 264
held for 3 min. The carrier gas (99.9995% nitrogen) flow rate was held at 1.5ml 265
min−1. MSD (mass selective detector) was operated in SIM (selected ion 266
monitoring) mode, with the electron energy at 70 eV, the EI (electron ionization) 267
source held at 175 °C and the interface temperature at 300 °C. 268
To analyze the nitro-PAHs, a 63Ni electron-capture detector (ECD) was 269
used for GC-ECD analysis under the same conditions as the PAH analyses. 270
The ECD temperature was 300°C, and the total gas flow rate was 30 ml min−1 271
(makeup plus column). In a preliminary investigation for the above conditions, 272
these PAHs and nitro-PAHs have a completely isolated chromatogram with 273
retention time ranging from 4.66 to 27.39 min. The mixed stock solution was 274
used to make five concentrations of mixed standard solution, which were 275
required to establish calibration curves for PAH and nitro-PAH measurement. 276
The injection volume was 1µ l for all samples. The spike was added to the 277
blank sampling PUF+XAD-16 and quartz filter prior to extraction for recovery 278
analysis. The average recovery of PAHs based on QA/QC ranged from 68% 279
(naphthalene) to 93% (pyrene) and 71% (naphthalene) to 94% 280
(Benzo(g,h,i)perylene) for the PUF+XAD-16 and quartz filter samples, 281
respectively. The nitro-PAHs had lower average recoveries for the 282
PUF+XAD-16 and quartz filter samples, which ranged from 59% 283
(1,3-Dinitropyrene) to 87% (2-Nitrofluorene) and 61% (1,8-Dinitropyrene) to 284
89% (3-Nitrofluoranthene), respectively. 285
To validate the analysis method of PAHs in diesel particulate matter, 286
NIST Standard Reference Material SRM 1650a was used. About 50 mg of 287
SRM 1650a, which approximates the composition of diesel particulate matter, 288
was used to examine the accuracy and reliability of the analysis method. 289
290
3. RESULTS AND DISCUSSION 291
292
3.1 Exhaust gas characteristics 293
The diesel fuel characteristics included carbon: 86.0%, hydrogen: 294
12.4%, heat value: 10821 cal g-1, aromatic content: 32.4%, sulfur content: 295
0.0341% etc. The fuel characteristics could affect the emission factors of 296
particulate matter. CO, CO2, NOx and HC for the entire cycle are summarized
297
in Table 2; some literature data are also included for comparison. The fuel 298
consumption of these light-duty diesel vehicles was in the range of 299
0.106-0.132 l km-1. The average emission factors of light-duty diesel vehicles 300
were 0.171, 0.158, 1.395, and 1.735 g km-1 for THC, NMHC, CO and NOx, 301
respectively. About 8% CH4 contributed to THC.
302
In general, the PM emission factors are low for low-mileage vehicles, 303
and the values increase with mileage accumulation and age. The average PM 304
emission factor was 0.1720.071 g km-1. High fuel consumption reflects high 305
CO2 and high NOx emission. In addition, little methane was emitted from the
306
diesel exhaust. LDV-4 was the lowest reference weight, but high fuel 307
consumption (about 20-50% high) and high pollution emission, i.e., CO (about 308
1.5-3.9 times), NOx (about 2.4-4.0 times). Results indicated that weight was 309
not the main factor in high fuel consumption; engine characteristics are also 310
important (Ceviz and Akin, 2010). High fuel consumption could cause 311
incomplete combustion for high CO and high engine temperature for high 312
thermal NOx. 313
PM, THC, CO, and NOx concentrations were in the range of California 314
test guidelines for 1998, which are based on the FTP driving cycle (Norbeck 315
etal., 1998). The average concentrations of PM and THC were low in this study, 316
which could be attributed to the age of the California vehicles (1977-1993). 317
These vehicles were older than those used in our tests. 318
319
3.2 PM mass distribution 320
Figure 1 shows the particle size distribution of the exhaust of light-duty 321
diesel vehicles. Particulate matter concentration was 172 mg km-1; 66% of 322
particulate mass fraction was less than 0.4 m (near the range of ultrafine 323
particles). In addition, particulate size was 0.4-0.6, 0.6-1.0, and 1.0-1.9 m 324
corresponding to mass fractions of 6, 8 and 6%, respectively. Other particle 325
size fractions were less than 4%. About 80% of the mass fraction of diesel 326
particulate was less than 1.0 m. Lin et al. (2008) indicated high mass fraction 327
at a particle size < 1.0 m, especially in the 0.166-0.52 m range, and low 328
mass fractions at particle sizes of > 0.52 m and < 0.166 m. Generally, the 329
high mass fraction was less than 0.4 m for diesel vehicles; the smallest cut 330
size of the particulate sampler is about 0.4 m, which could not clearly 331
describe the particle size distribution; it could be a limitation of this study. 332
Park et al. (2010) indicated that the mass concentration of diesel 333
nano-particles was in the range of 0.131-0.230 m. In addition, the average 334
sizes of particles emitted in diesel exhaust is higher than particles emitted in 335
gasoline exhaust under similar operating conditions. The peak of particle 336
concentrations for mineral diesel was never less 0.040 m; however, for 337
gasoline engines, it could be as low as 0.020 m under most operating 338
conditions (Gupta et al., 2010). 339 340 3.3 Particulate compositions 341 3.3.1 Carbon content 342
The emission factor of diesel particulate matter was about 172 mg km-1. 343
Based on the interception of particle size distribution, the emission factor of 344
PM10 was 167 mg km-1 and PM2.5 was 151 mg km-1. About 88% of particulate
345
mass was less than 2.5 m in diesel exhaust. Generally, the percent of 346
particulate mass less than 10 and 2.5 m was 99.4 and 95.1%, respectively 347
(Norbeck et al., 1998), which was higher than the results of this study. 348
The carbon content was high, and its fraction was about 72% of 349
particulate mass (Table 3). EC was about 66% of carbon content in particulate 350
mass; the remainder was OC in PM2.5. The fraction of EC was high compared
351
to the results (EC and OC were almost the same level) of Norbeck et al., 1998. 352
Generally, the EC content was higher than OC content in diesel particulate 353
matter (Kleeman et al., 1999; Grieshop et al., 2006), which was similar to this 354 study. 355 356 3.3.2 Elemental compositions 357
The emission factors of Al, S, Ca, and Fe were about 0.83-1.24 mg km-1 358
in PM2.5 and 1.07-1.77 mg km-1 in PM10, and the fractions of these elements
359
were about 66-90% in PM2.5 and others were in PM2.5-10. Sulfur content in fuel
360
could affect the formation of new particles during engine combustion in 361
exhaust gas. Sulfur could form sulfate after the cylinder gas, leaving as 362
exhaust. In addition, sulfur can be a catalyst poison in the exhaust control 363
system of diesel motor vehicles. (Kozak and Merkisz, 2005). Therefore, the 364
fuel sulfur could affect the formation of nucleation particulate matter during the 365
combustion of diesel fuel (Schneider et al., 2005). Some studies have 366
indicated that high sulfur and the oxidation catalyst are mandatory conditions 367
for sulfate formation, which results in nucleation formation of particulate matter 368
for light-duty diesel vehicles (Maricq et al., 2002; Vogt et al., 2003). 369
K, Zn, Na, and Mg were in the range of 0.18-0.48 mg km-1 in PM2.5 and
370
0.29-0.82 mg km-1 in PM10. Some toxic elements, i.e., Ni, Cr, Pb, Cu, Cd, and
371
As, ranged from 0.01-0.09 mg km-1 in PM2.5 and 0.02-0.22 mg km-1 in PM10.
372
Others were trace, i.e., Sb, Sr, V, and Se (the emission factors were less than 373
0.04 mg km-1 in PM2.5). The element content in PM could be attributed to the
374
engine wear and tear, pipe erosion of the vehicle, and fuel compositions (Wang 375 et al., 2003). 376 377 3.3.3 Ionic species 378
Nitrate (0.82 mg km-1 in PM2.5 and 1.33 mg/km in PM10), sulfate (0.69 mg
379
km-1 in PM2.5 and 0.85 mg km-1 in PM10), ammonium (0.41 mg km-1 in PM2.5
380
and 0.54 mg km-1 in PM10), nitrite (0.22 mg km-1 in PM2.5 and 0.49 mg km-1 in
381
PM10) were the major ionic species in diesel PM. Other ionic species were less
382
than 0.16 mg km-1. Nitrate, nitrite and ammonium could be the result of the fuel 383
composition and high-temperature combustion causing thermal NOx formation. 384
Sulfur content in diesel fuel could be an important reason for the presence of 385
sulfate in particulate matter (Maricq et al., 2002; Vogt et al., 2003). Shi and 386
Harrison (1999) indicated that sulfuric acid/water (emitted from the fuel sulfur 387
combustion) with subsequent condensation of organic substances in the diesel 388
exhaust and the other species (i.e., ammonia) could be involved in the 389
nucleation. In addition, Yu (2001) implied that chemiion could play a role in 390
diesel exhaust nucleation. 391
The ionic species contents were high in diesel PM compared to those 392
reported by Norbeck (1998). In addition, some alkali metals and alkali earth 393
metals (Na, K, Mg, and Ca) were less than 0.17 mg/km in diesel PM. 394
The determined composition fractions of PM2.5 were taken from diesel
395
exhaust shown as Figure 2. Carbon content was high in PM, with low 396
elements (3.8%) and ionic species (1.6). In addition, the composition of about 397
22% of PM mass could not be determined; it is a limitation of this study. 398
399
3.3.4 PAHs 400
The emission factors of PAHs are shown in Figure 3. Twenty-six PAHs 401
including 16 PAHs and 10 nitro-PAHs were determined for diesel vehicle 402
exhaust. The toxicity and cancer effects of PAHs are of greatest concern after 403
exposure. The IARC identifies some PAHs to be probable human carcinogens 404
(Group 2A, i.e. Benz(a)anthracene, benzo(a)pyrene, Dibenzo(a,h)anthracene 405
etc.) and others to be possible human carcinogens (Group 2B, i.e. 406
Benzo(b)fluoranthene (BbF), Benzo (k)fluoranthene (BkF), 407
Indeno(1,2,3-cd)pyrene (IND), 2-Nitrofluorene (2-nFlu), 1-Nitropyrene (1-nPyr), 408
6-Nitrochrysene (6-nCHR), 1,6-Dinitropyrene (1,6-DnPyr), 1,8-Dinitropyrene 409
(1,8-DnPyr) etc.) (IARC, 1983 and 2010). In addition, some PAHs have been 410
classified in Group 3, a class of chemicals for which no human data is available 411
on carcinogenesis and there is only limited or inadequate data in animals (i.e. 412
Benzo(g,h,i)perylene (BghiP); 9-Nitroanthracene (9-nAnt), 3-Nitrofluoranthene 413
(3-nFL), 7-Nitrobenzo(a)anthracene (7-nBaA), 1,3-Dinitropyrene (1,3-DnPyr), 414
6-Nitrobenzo(a)pyrene (6-nBaP) etc) (IARC, 1983 and 2010). Therefore, these 415
PAHs are of concern due to their volatilization in diesel exhaust, persistent 416
organic pollutants in the environment and toxicity in human health effect. 417
The emission factor of total PAHs was 3.62 mg km-1 in this study; about 418
40% was in the gas phase and 60% in the particulate phase (20% was 419
determined in the particulate size > 1.9 m, and 10% was in the particulate 420
size less than 0.4m). Naphthalene, acenaphylene, fluoranthene, fluorine, 421
anthracene, pyrene, acenaphthene and phenanthrene are dominant PAHs, 422
and their emission factors were over 0.12 mg km-1. Naphthalene and indeno 423
(1,2,3-cd) pyrene were dominant in the gas phase. We used the concept of 424
toxic equivalent factor (TEF) to determine the carcinogenicity of chemicals. 425
TEF data was investigated by LaGoy and Nisbet’s study. In many risk 426
assessments of complex pollutant mixtures, all carcinogenic PAHs have been 427
considered to be as carcinogenic as BaP (Marty et al., 1994). Sixteen PAHs 428
were transferred to TEF as BaP. Results indicated that the TEF of 16 PAHs 429
was 0.24 mg-BaP km-1 and the Dibenzo(a,h)anthracene and BaP was about 430
90% TEF in diesel exhaust. 431
The content of nitro-PAHs (shown as Figure 4) was low, with most less 432
than 0.04 mg/km. The emission factors of 1,6-dinitropyrene, 2-nitrofluorene 433
and 1,8—dinitropyrene were in the range of 0.019-0.040 mg km-1
. The mass 434
fraction of nitro-PAHs in total PAHs was less than 4%. But some nitrated 435
aromatic hydrocarbons--i.e., 1,6-Dinitropyrene, 1,8-Dinitropyrene, 436
6-Nitrochrysene, etc.--revealed high toxic potency, with the potential for 437
mutagenic and carcinogenic effects related to cell apoptosis of diesel exhaust 438
(Landvik et al., 2007). 439
Only PAHs and nitro-PAHs were determined in PM contributing to low 440
mass fraction of organic carbon in this work. Generally, PM organic classes 441
included the n-alkanes and acids from C13-30, PAHs, oxygenated/sulfur
442
containing PAHs, hopanes, steranes, methoxylated phenols and others 443 (Mcdonald et al., 2004). 444 445 4. CONCLUSIONS 446
Six light-duty diesel vehicles were selected to determine the pollutant emission 447
factor of exhaust and following the FTP-75 driving cycle in a dynamometer. 448
Fuel consumption was 0.1260.022 l km-1, and the high fuel consumption 449
reflects high CO2 and NOx emissions. The average emission factor of PM was
0.1720.071 g km-1, THC was 0.1710.137 g km-1, CO was 1.3950.698 g 451
km-1, and NOx was 1.7351.127 g km-1. Carbon content was about 72% of 452
particulate mass, and the EC portion was about 66% of carbon content, with 453
the remainder being OC. Al, S, Ca, and Fe were about 1.0 mg/km,and K, Zn, 454
Na, and Mg were less than 0.50 mg km-1 in PM2.5. Some toxic elements, i.e., Ni,
455
Cr, Pb, Cu, Cd, and As, were less than 0.1 mg km-1 and others were trace; i.e., 456
Sb, Sr, V, and Se were less than 0.04 mg km-1 in PM2.5. Nitrate, sulfate,
457
ammonium, and nitrite were the major ionic species, and their emission factor 458
was 0.22 (nitrite)-0.82 (nitrate) mg km-1 in diesel PM2.5. The emission factor of
459
total PAHs was 3.62 mg km-1, and their mass was about 60% in the particulate 460
phase. Emission factors of naphthalene, acenaphylene, fluoranthene, 461
fluorine, anthracene, pyrene, acenaphthene and phenanthrene were in the 462
range of 0.13-1.04 mg km-1. The mass fraction of nitro-PAHs in total PAH was 463
less than 4%, and1,6-dinitropyrene, 2-nitrofluorene and 1,8—dinitropyrene 464
were in the range of 0.019-0.040 mg km-1. 465
466
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687
Tables 688
Table 1 Information of testing light-duty diesel vehicles 689
Table 2 Exhaust emission factor (g km-1) of light-duty diesel vehicle 690
Table 3 Chemical constituents (mg km-1) of particulate matter of light-duty 691
diesel vehicles 692
Figures 693
Figure 1 Particle size distribution of light-duty diesel vehicles 694
Figure 2 Composition fraction of PM2.5 of light-duty diesel vehicle exhaust
695
Figure 3 PAH emission factor of light-duty diesel vehicle exhaust 696
Figure 4 Nitro-PAH emission factor of light-duty diesel vehicle exhaust 697
