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Assessment of Exposures to Mobile Source Air Toxics
Eric M. FujitaBarbara Zielinska
Division of Atmospheric SciencesDesert Research Institute
Reno, NV
Air Toxics Workshop IIHouston, Texas
June 12-13, 2007
Desert Research Institute June 12, 2007
Estimating Exposures to MSAT Ambient concentrations at fixed sites versus vehicle dominated
microenvironments.
Time spent in various microenvironments by population groups.
Ambient versus personal breathing zone concentrations.
Variations in pollutant concentrations and composition in mobile source dominated locations. Spatial variations due to proximity.
Temporal variations (diurnal, daily, day-of-week, and seasonal).
Traffic mix (diesel vs. gasoline, gross polluters vs. normal emitters, vehicle operating mode).
Atmospheric transformation (chemical and physical).
Assessing Exposures to MSATs
Desert Research Institute June 12, 2007
Acknowledgments• Comparative Toxicity Study
– Sponsor: DOE’s Office of FreedomCAR and Vehicle Technologies
• Weekend Ozone Study– Sponsor: DOE’s Office of FreedomCAR and Vehicle Technologies; Coordinating Research Council
– Additional Support: South Coast Air Quality Management District
• Gasoline/Diesel PM Split Study– Sponsor: DOE’s Office of FreedomCAR and Vehicle Technologies
– Additional Support: U.S. Environmental Protection Agency. California Bureau of Automotive Repair, South Coast Air Quality Management District, Ralph’s Supermarket Distribution Center
• Kansas City Vehicle Characterization Study– Sponsor: U.S. Environmental Protection Agency Office of Transportation and Air Quality
– Additional Support: DOE’s Office of FreedomCAR and Vehicle Technologies, Coordinating Research Council, U.S. Federal Highway Administration.
• Section 211(B) Tier 2 High End Exposures – Sponsor: American Petroleum Institute
– Additional Input: U.S. Environmental Protection Agency
• Assessing Exposure to Air Toxics in Microenvironments Dominated by Mobile Sources – Sponsor: Health Effects Institute
– Additional Support: South Coast Air Quality Management District.
• Atmospheric Transformations of Diesel Exhaust – Sponsor: Health Effects Institute
References
Desert Research Institute June 12, 2007
Fujita, E.M., D.E. Campbell, B. Zielinska, J.C. Sagebiel, J.L. Bowen, W. Goliff, W.R. Stockwell, and D.R. Lawson (2003). Diurnal and Weekday Variations in Source Contributions of Ozone Precursors in California’s South Coast Air Basin. J. Air & Waste Manage. Assoc. 53: 844-863.
Zielinska, B., W.S. Goliff, M. McDaniel, T. Cahill, D. Kittleson and W. Watts (2003). Chemical Analyses of Collected Diesel Particulate Matter Samples in the CRC E-43 Project. Prepared for the National Renewable Energy Laboratory, Golden, CO.
Zielinska, B. J. Sagebiel, J.D. McDonald, K. Whitney and D.R. Lawson (2004). Emission Rates and Comparative Chemical Composition from Selected In-Use Diesel and Gasoline-Fueled Vehicles. J. Air & Waste Manage. Assoc. 54:1138-1150.
Fujita, E.M. and D.E. Campbell (2006). Spatial and Temporal Variations in Exposure to Air Toxics in the South Coast Air Basin. Final report submitted by Desert Research Institute to the National Renewable Energy Laboratory, Golden, CO, August 31, 2006.
Fujita, E.M., D.E. Campbell, B. Zielinska, W.P. Arnott and J.C. Chow (2007). Exposure to Air Toxics in Mobile Source Dominated Microenvironments. Draft report submitted by Desert Research Institute to the Health Effects Institute, Boston, MA, February 6, 2007.
Fujita, E.M., B. Zielinska, D.E. Campbell, W.P. Arnott, J. Sagebiel, L. Reinhart, J.C. Chow, N. P.A. Gabele, W. Crews, R. Snow, N. Clark, S. Wayne and D.R. Lawson (2007). Variations in speciated emissions from spark-ignition and compression ignition motor vehicles in the California's South Coast Air Basin. J. Air & Waste Manage. Assoc. 57:705-720.
Fujita, E. M., D. E. Campbell, W. P. Arnott, B. Zielinska (2007). Evaluations Of Source Apportionment Methods for Determining Contributions Of Gasoline and Diesel Exhaust to Ambient Carbonaceous Aerosols. J. Air & Waste Manage. Assoc. 57:721-740.
Zielinska, B., J. Sagebiel, S. Samy, JC. Seagrave, J. McDonald, P. Wiesen and K. Wirtz (2007) Atmospheric Transformation of Diesel Emissions, Poster presented at 2006 HEI Annual Conference, Chicago, Il, April 15-17, 2006.
Average Hourly Light-Duty and Heavy-Duty Traffic Volumes Weigh-in-Motion Sites in Interior of South Coast Air Basin
Desert Research Institute June 12, 2007
DOE NREL Weekend Ozone StudyCourtesy of Sonoma Technology, Inc., 2002
Heavy-Duty
Light-Duty
Photoacoustic Black Carbon (1-minute averages)
Desert Research Institute June 12, 2007
Gasoline/Diesel PM Split Study
Sunday
Weekday
Weekday Variations in CO and Black Carbon at Azusa9/30/00 to 10/8/00 - Weekend Ozone Study
Desert Research Institute June 12, 2007
0
1
2
3
4
50:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
00:
006:
0012
:00
18:0
0
Sat, 9/30 Sun, 10/1 Mon, 10/2 Tue, 10/3 Wed, 10/4 Thu, 10/5 Fri, 10/6 Sat, 10/7 Sun, 10/8
bla
ck c
arb
on
(u
g/m
3)
0
0.5
1
1.5
2
2.5
3
CO
(p
pm
)
Black Carbon (ug/m3)
CO (ppm)
Weekend Ozone Study
Desert Research Institute June 12, 2007
0
100
200
300
400
500
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
0:0
06
:00
12
:00
18
:00
Sat, 9/30 Sun, 10/1 Mon, 10/2 Tue, 10/3 Wed, 10/4 Thu, 10/5 Fri, 10/6 Sat, 10/7 Sun, 10/8
NM
HC
(p
pb
C)
0.0
0.4
0.8
1.2
1.6
2.0
CO
(p
pm
)
NMHC
CO (ppm)0
1
2
3
4
5
0:0
0
6:0
01
2:0
01
8:0
00
:00
6:0
01
2:0
0
18
:00
0:0
06
:00
12
:00
18
:00
0:0
0
6:0
01
2:0
01
8:0
00
:00
6:0
01
2:0
0
18
:00
0:0
06
:00
12
:00
18
:00
0:0
0
6:0
01
2:0
01
8:0
00
:00
6:0
01
2:0
0
18
:00
0:0
06
:00
12
:00
18
:00
Sat, 9/30 Sun, 10/1 Mon, 10/2 Tue, 10/3 Wed, 10/4 Thu, 10/5 Fri, 10/6 Sat, 10/7 Sun, 10/8
bla
ck
ca
rbo
n (
ug
/m3
)
0
20
40
60
80
100
NO
x (
pp
b)
BC (ug/m3)
NOx (ppb)
Weekday Variations in BC & NOx versus CO & NMHC at Azusa9/30/00 to 10/8/00 - Weekend Ozone Study
BC and NOx
CO and NMHC
Weekend Ozone Study
CMB Source Contribution Estimates for Total Carbonat Azusa, Los Angeles and Other Sites
Desert Research Institute June 12, 2007
Total Carbon (IMPROVE)
0.0
0.2
0.4
0.6
0.8
1.0
Fra
ctio
nal
SC
E
Diesel Gasoline Residual
Total Carbon (STN)
0.0
0.2
0.4
0.6
0.8
1.0
Azu
sa
Su
n
Azu
sa
Mo
n
Azu
sa
Tu
e
Azu
sa
We
d
Azu
sa
Th
u
Azu
sa
Fri
Azu
sa
Sa
t
LA
NM
S
un
LA
NM
M
on
LA
NM
T
ue
LA
NM
W
ed
LA
NM
T
hu
LA
NM
F
ri
LA
NM
S
at
Sa
n D
ima
s M
on
Ve
nic
e S
at
Ro
se B
ow
l Sa
t
I-4
05
Su
n
Fra
ctio
nal
SC
E
Gasoline/Diesel PM Split Study
Mainly diesel at Azusa and LA, but mixed at other sites
Large residual fraction.
Desert Research Institute June 12, 2007
CMB Source Contribution Estimates for Benzene & Toluene
Benzene
0.0
1.0
2.0
3.0
4.0
5.0
1999 2000 1999 2000 1999 2000 1999 2000
Azusa Los Angeles N.Main
Pico Rivera Upland
pp
b
Gasoline Exhaust Gasoline Vapor Gasoline Liquid
Diesel Exhaust Coatings Consumer Products
Toluene
0.0
4.0
8.0
12.0
16.0
1999 2000 1999 2000 1999 2000 1999 2000
Azusa Los Angeles N.Main
Pico Rivera Upland
pp
b
Weekend Ozone Study
DustTrak PM mass (ug/m3) for Phase 2 of the LA92 CycleSummer Study
Stratum 5 (pre-81)Stratum 6 (1981-90)
Stratum 7 (1991-95)Stratum 8 (1996+)
Kansas City Vehicle Emissions Characterization Study
Desert Research Institute June 12, 2007
Ascending PM2.5 Emission Rates within Model Year GroupsKansas City Vehicle Emissions Characterization Study
0
50
100
150
200
250
300
350
400
Emissions in Ascending Order wihin Model Year Groups
PM
Em
issi
on
Rat
es,
mg
/mil
e
Ascending Age
High emitters contributed a disproportionate share of the PM emissions (17% in Round 1 and 24% in Round 2 contribute 75% of the total).
Source: EPA OTAQ
Desert Research Institute June 12, 2007
Kansas City Vehicle Characterization Study- Summer Volatile, Semi-Volatile and Particulate PAHs
Emissions of Total PAHs (mg/mile)
0
40
80
120
160
S1
-1S
1-2
S2
-1S
2-2
S2
-3S
2-4
S3
-1S
3-2
S4
-1S
4-2
S5
-1S
5-2
S5
-3S
5-4
S5
-5S
6-1
S6
-2S
6-3
S6
-4S
7-1
S7
-2S
7-3
S7
-4S
8-1
S8
-2S
8-3
Trucks Cars
Em
iss
ion
s (
mg
/mile
)
26 other PAHs indeno[123-cd]pyrenebenzo(ghi)perylene coronene63 Volatile and SV PAHs 1-methylnaphthalene2-methylnaphthalene napthalene
Total PAHs (% of Total)
0%
25%
50%
75%
100%
S1-
1S
1-2
S2-
1S
2-2
S2-
3S
2-4
S3-
1S
3-2
S4-
1S
4-2
S5-
1S
5-2
S5-
3S
5-4
S5-
5S
6-1
S6-
2S
6-3
S6-
4S
7-1
S7-
2S
7-3
S7-
4S
8-1
S8-
2S
8-3
Trucks Cars
Pe
rce
nt
26 other PAHs indeno[123-cd]pyrenebenzo(ghi)perylene coronene63 Volatile and SV PAHs 1-methylnaphthalene2-methylnaphthalene napthalene
Desert Research Institute June 12, 2007
Kansas City Vehicle Characterization Study
Comparative Emissions and Toxicity of Gasoline and Diesel Vehicles
Desert Research Institute June 12, 2007
0
5000
10000
15000
20000
25000
30000
35000
40000
F P F P F P F P F P F P F P F P
ug
/mile
naphth menaph dmenaph mebiph tmenaph acnapy acnape fluore phenan meflu fl9one
xanone mephen anrquone dmephen anthra fluora pyrene mepy/fl bzcphen baanth chrysn
bbjkfl bepyrn bapyrn incdpy bghipe dbanth corone
-----G------
-----BG----
------WG-----
-----D----------HD----
---G30 --- ---D-30 ---
----NG---
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
G BG WG D HD G30 D30 NG
Filter Only
0
200
400
600
800
1000
1200
1400
1600
G BG D HD G30 D30 NG
Gasoline VehiclesG: Average Gasoline at 72° FBG: Black Smoker at 72° FWG: White Smoker at 72° FG30: G at 30° FNG: New Technology
Diesel Vehicles D: Average Diesel at 72° FHD: High PM Emitter at 72° FD30: D at 30° F
F = FilterP = PUF/XAD
In Vivo Toxicity Per Unit Mass
• Gs ~ Ds in nature and potency• High G & D > Normal G & D
Seagrave et al., Toxicol. Sci.,70, 212-226, 2002
Chamber Reaction of Toluene with Diesel ExhaustOpen Path FTIR Data
Desert Research Institute June 12, 2007
HEI Study – Atmospheric Transformations of Diesel Exhaust
Diesel Exhaust + Toluene, Light
0
10
20
30
40
50
60
70
7:48
8:08
8:28
8:48
9:08
9:28
9:48
10:0
8
10:2
8
10:4
8
11:0
8
11:2
8
11:4
8
12:0
8
12:2
8
12:4
9
13:0
9
13:2
9
13:4
9
14:1
0
14:3
0
14:5
1
15:1
1
15:3
2
15:5
2
16:1
3
16:3
4
16:5
4
Time (GMT)
pp
b (
HC
HO
, H
CO
OH
, G
lyo
xal,
P
AN
, H
NO
3)
0
100
200
300
400
500
600
700
pp
b (
NO
x, O
3, T
olu
ene)
HCHO HCOOH Glyoxal PAN HNO3 Nox O3 Toluene
Toluene
NOx
Ozone
PAN-like
Glyoxal
HNO3
HCOH
HCOOH
May 19, 2005
Time Evolution of Diesel Exhaust Particle Size Distributions with Photochemical Reactions of Toluene
Desert Research Institute June 12, 2007
Particle Size distribution Chamber B
0
10000
20000
30000
40000
50000
60000
70000
80000
0 50 100 150 200 250 300
Dp (nm)
dN
/dL
og
Dp
(#
/cm
3 )
8:10:23
10:40:20
13:40:16
5/19/2005
• Addition of ~500 ppb of toluene (NOx ~100 ppb) resulted in a substantial secondary aerosol formation.
• Initial DPM concentration: 9 µg/m3
• peak PM concentration: 57 µg/m3
HEI Study – Atmospheric Transformations of Diesel Exhaust
Particle Number Concentration Distribution at the Tuscarora Tunnel, 5/21/99
Desert Research Institute June 12, 2007
TunnelInlet
Tunneloutlet
RegionalBackground
* Source: HEI Project 98-3 courtesy of Dr. Fred Rogers, Desert Research Institute.
Concentration Distributions on nano-MOUDI Stagesof Organic Compounds in Diesel Exhaust (Light Cruise)
Desert Research Institute June 12, 2007
Source: Zielinska et al. 2003, Project Report for CRC-E43.
Semi-volatile PAH
0
10
20
30
40
50
60
0.0
10
0.0
18
0.0
32
0.0
56
0.1
00
0.1
80
0.3
20
0.5
60
1.0
00
1.8
00
3.2
00
5.6
20
10
.00
0
ng
/m3
dmph fluora
pyrene mfl/mpy
bzcphen baanth
chrysn
Particle PAH
0.0
0.5
1.0
1.5
2.0
0.0
10
0.0
18
0.0
32
0.0
56
0.1
00
0.1
80
0.3
20
0.5
60
1.0
00
1.8
00
3.2
00
5.6
20
10
.00
0
nano-MOUDI stages (um)
ng
/m3
bbjkfl bepyrn
bapyrn incdpy
bghipe dbanth
corone
Hopanes & Steranes
0
100
200
300
400
500
0.0
10
0.0
18
0.0
32
0.0
56
0.1
00
0.1
80
0.3
20
0.5
60
1.0
00
1.8
00
3.2
00
5.6
20
10
.00
0
nano-MOUDI stages (um)
ng
/m3
Steranes
Hopanes
Total Alkanes
0
10000
20000
30000
40000
500000
.01
0
0.0
18
0.0
32
0.0
56
0.1
00
0.1
80
0.3
20
ng
/m3
Desert Research Institute June 12, 2007
Health Effects Institute Project RFA03-1
Black Carbon (1-minute) by Photoacoustic
Sampling Location
ug
/m3
BC - 1 minute averages, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood-15
0
15
30
45
60
75
90
105
120
135
150
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
ug
/m3
PM2.5 - 1 minute averages, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood-40
0
40
80
120
160
200
240
280
320
360
400
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
pp
bV
BTEX - 1 minute surrogate & 24hr canisters, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood0
4
8
12
16
20
24
28
32
36
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
pp
bV
1,3 butdiene - 1 minute surrogate & 24hr canisters, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
3.6
4
MaximumMinimum75%25%MedianOutliersExtremes
Figure 3. Box and whisker plots of one-minute black carbon and PM 2.5 (DustTrak) concentrations. DustTrak exceeds gravimetric mass measurements by a factor of 2 to 2.5. Correlations of time-averaged PID and canisters measurements were used to reconstruct one-minute BTEX and 1,3-butadiene mixing ratios.
Ranges in On- and Near-Road Exposure
Sampling Location
ug
/m3
BC - 1 minute averages, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood-15
0
15
30
45
60
75
90
105
120
135
150
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
ug
/m3
PM2.5 - 1 minute averages, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood-40
0
40
80
120
160
200
240
280
320
360
400
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
pp
bV
BTEX - 1 minute surrogate & 24hr canisters, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood0
4
8
12
16
20
24
28
32
36
MaximumMinimum75%25%MedianOutliersExtremes
Sampling Location
pp
bV
1,3 butdiene - 1 minute surrogate & 24hr canisters, September
110 Fwy 405 Fwy 60 Fwy Truck Rt. Dmnd Bar LongBeach Lynwood0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
3.6
4
MaximumMinimum75%25%MedianOutliersExtremes
Figure 3. Box and whisker plots of one-minute black carbon and PM 2.5 (DustTrak) concentrations. DustTrak exceeds gravimetric mass measurements by a factor of 2 to 2.5. Correlations of time-averaged PID and canisters measurements were used to reconstruct one-minute BTEX and 1,3-butadiene mixing ratios.
Ranges in On- and Near-Road Exposure405
110
60
710605
91
Long Beach
Diamond Bar
Lynwood
Comparisons of On-Road Versus Fixed StationSummer Morning CO
Desert Research Institute June 12, 2007
Health Effects Institute Project RFA03-1
Comparisons of On-Road Versus Fixed StationSummer Morning NOx
Desert Research Institute June 12, 2007
Health Effects Institute Project RFA03-1
Distributions of BTEX Exposures in Atlanta MEs
Desert Research Institute June 12, 2007
Sum BTEX
2.4
132
9.2
14.2
1.4
65
10.1
9.8
1.3
583
18.0
40.0
3.1
304
17.5
25.8
0.6
25
3.7
7.3
2.2
2454
13.3
97.6
0.8
58
5.1
5.8
2.6
80
7.0
9.4
2.1
98
14.1
24.3
60.1
465
152.4
172.1
5.8
40
11.7
13.3
2.9
533
11.9
29.7
ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 ME12 ME13
0
20
40
60
80
100
120
Sum BTEX
2.4
132
9.2
14.2
1.4
65
10.1
9.8
1.3
583
18.0
40.0
3.1
304
17.5
25.8
0.6
25
3.7
7.3
2.2
2454
13.3
97.6
0.8
58
5.1
5.8
2.6
80
7.0
9.4
2.1
98
14.1
24.3
60.1
465
152.4
172.1
5.8
40
11.7
13.3
2.9
533
11.9
29.7
ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 ME12 ME13
0
20
40
60
80
100
120
Sum BTEX
2.4
132
9.2
14.2
1.4
65
10.1
9.8
1.3
583
18.0
40.0
3.1
304
17.5
25.8
0.6
25
3.7
7.3
2.2
2454
13.3
97.6
0.8
58
5.1
5.8
2.6
80
7.0
9.4
2.1
98
14.1
24.3
60.1
465
152.4
172.1
5.8
40
11.7
13.3
2.9
533
11.9
29.7
ME1 ME2 ME3 ME4 ME5 ME7 ME8 ME8_9 ME10 ME11 ME12 ME13
0
20
40
60
80
100
120
1. In-Cabin Congested Freeway 5. In-Cabin Toll Plaza 10. Outdoor Surface Parking2. In-Cabin Urban Canyon 7. Outdoor Refueling 11. Outdoor Underground Garage3. In-Cabin Refueling 8. Sidewalk 12. Outdoor Toll Plaza4. In-Cabin Underground Garage 9. Sidewalk/Bus Stop 13. Following High Emitters
1st Qtr
Max
Min
3rd Qtr
Med
Ave
API Section 211(B) Tier 2 Exposure Study
132 65 583 304 25 2454 58 80 46598 40 533
Mean ME to Air Monitoring Station Ratiosof MSAT for Corresponding Hours - Houston
Desert Research Institute June 12, 2007
Houston- Summer
1
10
100
1000
10000
1 2 3 4 5 6 7 8 9 10 11 12
Microenvironment
ME
/Sta
tio
n R
ati
o
Benzene
Toluene
m&p-Xylenes
Houston - Winter
1
10
100
1000
10000
1 2 3 4 5 6 7 8 9 10 11 12
Microenvironment
ME
/Sta
tio
n R
ati
o
Log Scale
1. In-vehicle congested freeway 5. In-vehicle toll plaza 9. Outdoor bus stop
2. In-vehicle urban canyon 6. In-vehicle road tunnel 10. Outdoor surface parking
3. In-vehicle refueling 7. Outdoor refueling 11. Outdoor underground garage
4. In-vehicle underground garage 8. Outdoor sidewalk 12. Outdoor toll plaza
API Section 211(B) Tier 2 Exposure Study
• Ambient levels of volatile organic MSATs in the SoCAB were mainly associated with gasoline vehicles.
– On-road CO, NMHC, and volatile MSATs were 2-5 times higher than fixed monitoring sites (1-hour averages).
• Diesel vehicles were the dominant mobile source of EC and TC at two fixed monitoring sites (Azusa and Los Angeles).
– However source contributions of gasoline and diesel vehicles varied with location and time.
– On-road NO and BC were about an order of magnitude higher than at fixed monitoring sites (1-hour averages).
• Short-term on-road exposures (few minute or less) can be substantially higher (10 to 100 times higher) and depend on proximity of high gasoline emitters and diesel trucks.
• Over half of the organic carbon during summer in the SoCAB could not be apportioned to directly-emitted PM emissions from motor vehicles.
– Gasoline vehicles are predominant source of anthropogenic SOA precursors (volatile and semi-volatile aromatic hydrocarbons.
• Concentrations of ultrafine particles (<0.1 m) are greatest in fresh emissions and rapidly grow to accumulation size particles (0.1 to 1.0 m).
• High emitters contributed a disproportionate share of the PM emissions (about 20% of the vehicles contributed 75% of the total).
Summary and Conclusions
Desert Research Institute June 12, 2007
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