Exposure to Ultrafine Particles

on and Near Roadways

Yifang Zhu , Ph.D.

Associate Professor

Environmental Health Sciences Department

Fielding School of Public Health

University of California Los Angeles

2

PM10(10 µµµµm)

PM2.5

(2.5 µµµµm)

Ultrafine PM

(0.1 µµµµm)

Human Hair(60 µm diameter)

PM2.5

(2.5 µµµµm)

PM10

(10 µµµµm)

Relative size of particles

Comparison of PM10, PM2.5, and Ultrafine PM

Ultrafine PM PM2.5 PM10

Hinds, 1999, “Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles”, 2nd edition.

Number

Distribution

Mass

Distribution

Atmospheric Aerosols: Particulate Matter (PM) Size Distribution

4

Respiratory Deposition, fraction

0.0

.2

.4

.6

.8

1.0

Particle Diameter (nm)

1 10 100 1000 10000

Number Weighted

Mass Weighted

Head Airways

Tracheobronchial

Alveolar

Particle Regional Deposition for Light Exercise

5

Translocation of UFP from

NP and TB region along sensory

neurons to CNS (neurodegeneration)

•Translocation of UFP to

interstitium, capillaries, heart

•Uptake by endothelium; platelets

•Activation/interaction of endothelial

cells, platelets and leukocytes

Alveolar inflammation

Pathways of Particle Translocation Within and Outside Respiratory Tract

6

Vehicular emissions usually constitute the most

significant source of UFPs in an urban environment.

7

Recent Traffic-Related Health Studies

� Cardiac and Pulmonary Health Risks from Near-

Highway ExposuresEnvironmental Health – Tufts Univ. School of Medicine (Brugge 2007)

� Adverse Effects of Traffic Exposure on Children’s

Lung DevelopmentThe Lancet – USC School of Medicine (Gauderman 2007)

� Traffic Exposure and Decreased Lung Function in

Adults with AsthmaA,. Academy of Allergy, Asthma & Immunology – UCSF (Balmes 2009)

� Residential Proximity to Freeways and Autism in the

CHARGE Study Environmental Health Perspectives – USC School of Medicine (Volk, 2011)

8

I-405

Freeway

I-405

Freeway

I-710

Freeway

I-710

Freeway

Upwind DownwindUpwind Downwind

Near Roadways

Key

pointUFP concentrations decay

exponentially downwind of freeways.

Zhu et al., 2002 “Concentration and size

distribution of ultrafine particles near a major

highway”, J. of Air and Waste Management

Association, 52:1032-1042.

Zhu et al., 2002 “Study of Ultrafine Particles near a

Major Highway with Heavy-duty Diesel Traffic”,

2002, Atmospheric Environment, 36: 4323-4335.

9

10

11

Diurnal Pattern of Pollutant Concentration in LA

Kim S, Shen S, Sioutas C. 2002, Size distribution and diurnal and seasonal trends of ultrafine particles in source and receptor sites of

the Los Angeles basin, J Air Waste Manag Assoc. Mar; 52(3):297-307.

12

Distance from the freeway (m)

500 400 300 200 100 0 100 200 300 400 500

Total Particle Number Concentration (cm

-3)

0.0

2.0e+4

4.0e+4

6.0e+4

8.0e+4

1.0e+5

1.2e+5

1.4e+5

1.6e+5

1.8e+5

2.0e+5

Freeway 405 Eastern SideLA National Cemetery

Western SideVA Facility

Daytime Dominant Wind

Nighttime Dominant Wind

Key

point

Daily exposure to UFPs: Three folds of

difference between the two cases.

Zhu et al., 2006, “Comparison of Daytime and Nighttime Concentration Profiles and Size Distributions

of Ultrafine Particles near a Major Highway” Environmental Science and Technology 40: 2531-2536.

Near Roadways

13Zhu et al., 2005 “Penetration of freeway ultrafine particles into indoor environments”, 2005, Journal of Aerosol

Science, 36: 303-322.

� Apartment 1

� Apartment 2

Particle Diameter (nm)

Key

point

Significant amount of freeway UFPs

penetrate into indoor environments.

Indoor near Roadways

14

405 FWY710 FWY

110 FWY

Jetta (2002) Audi A4 (2004) PT Cruiser (2005)

In-Cabin on Roadway

Zhu et al., 2007 , “In-cabin commuter exposure to ultrafine particles on Los Angeles freeways”.

Environmental Science and Technology. 41: 2138-2145.

15

(a) I-405

(b) I-710

Typical contour

plots of particle

number based

size distributions

inside a test

vehicle driving

on freeways.

Zhu et al., 2008 “Measurements of Ultrafine Particles and Other Vehicular Pollutants inside a Mobile Exposure System

on Los Angeles Freeways” J. of Air and Waste Management Association, 58: 424-434.

Key

point

Greater particle number

concentrations were

observed on I-710, a diesel

vehicle dominated freeway.

In-Cabin on Roadway

16Zhu et al., 2007 , “In-cabin commuter exposure to ultrafine particles on Los Angeles freeways”.

Environmental Science and Technology. 41: 2138-2145.

In-Cabin on Roadways

17Zhu et al., 2007 , “In-cabin commuter exposure to ultrafine particles on Los Angeles freeways”.

Environmental Science and Technology. 41: 2138-2145.

Key

point

Fan on & Recirculation on

provides the best protection

for UFP exposures.

In-Cabin on Roadways

18

Source

Sink

FiltrationPenetration

Recirculation Inhalation Coagulation Deposition

Supply, Qs

Recirculation, Qr

Penetration, QL

Filtration, ηηηηs

Breath rate, QF

Deposition, ββββ

Qs+QL

0

(1 )

( )

i mi S S L

mo F F S L

C C Q QP

C C Q V Q Q

η

η β

− += =

+ + +

In-Cabin Model

particle diameter,µm

0.01 0.1

I/O ratio

0.0

0.2

0.4

0.6

0.8

1.0

Model range

Model averageMeasured data

particle diameter,µm

0.01 0.1

I/O ratio

0.0

0.2

0.4

0.6

0.8

1.0

Model range

Model average

Measured data

particle diameter,µm

0.01 0.1

I/O ratio

0.0

0.2

0.4

0.6

0.8

1.0

Model range

Model average

Measured data

Fan off, RC off

Fan on, RC off

Fan on, RC on

In-Cabin Model

Bin Xu and Yifang Zhu “Quantitative analysis of the parameters affecting in-cabin to on-roadway (I/O)

ultrafine particle concentration ratios”, 2009, Aerosol Science and Technology, 43: 400-410.

Model performance under steady-state conditions

Time, min

0 20 40 60 80 100

UFP concentration, #/cm3

0

10000

20000

30000

40000

50000

Outdoor

Incabin-measured

Incabin-model

Model performance under dynamic conditions

In-Cabin Model

Bin Xu and Yifang Zhu “Quantitative analysis of the parameters affecting in-cabin to on-roadway (I/O)

ultrafine particle concentration ratios”, 2009, Aerosol Science and Technology, 43: 400-410.

Mechanical Airflow

Penetration Factor

Deposition Efficient

Filter Efficiency

Respiratory

Fan off, RC off

Fan on, RC off

Fan on, RC on

Xu and Zhu 2009 “Quantitative analysis of the parameters affecting in-cabin to on-roadway (I/O) ultrafine particle

concentration ratios”, Aerosol Science and Technology, 43: 400-410.

In-Cabin Model

Key

point

Penetration, Deposition, and

Filtration are important factors.

22

� Apparatus Configuration

Material Size Configuration

Rubber-Steel

0.8 mm height, 9.5 mm length straight-through

0.8 mm height, 28.5 mm length straight-through

1.6 mm height, 9.5 mm length straight-through

1.6 mm height, 28.5 mm length straight-through

Rubber-Rubber

0.8 mm height, 9.5 mm length straight-through

0.8 mm height, 28.5 mm length straight-through

Rubber-glass 0.8 mm height, 28.5 mm length double-bend

Penetration

23

Penetration factors as a function of

particle size under various

differential pressures

Particle diameter, nm

10 100

Penetration factor

0.5

0.6

0.7

0.8

0.9

1.0

30 Pa

80 Pa

120 Pa

160 Pa

200 Pa(b)Particle diameter, nm

10 100

Penetration factor

0.5

0.6

0.7

0.8

0.9

1.0

30 Pa

80 Pa

120 Pa

160 Pa

200 Pa(a)

Particle diameter, nm

10 100

Penetration factor

0.5

0.6

0.7

0.8

0.9

1.0

30 Pa

80 Pa

120 Pa

160 Pa

200 Pa(c)

Penetration

Key

point

Penetration factors increase as

particle size and differential

pressure increase.

Bin Xu, Shusen Liu, and Yifang Zhu “Ultrafine particle penetration through idealized vehicle cracks”,

2010, Journal of Aerosols Science, 41(9) 859-868.

24

�Particle penetration factor for

different crack lengths

Particle diameter, nm

10 100

Penetration factor

0.70

0.75

0.80

0.85

0.90

0.95

1.00

Crack length-28.5 mm

Crack length-9.5 mm

Particle diameter, nm

10 100

Penetration factor

0.70

0.75

0.80

0.85

0.90

0.95

1.00

Crack height-1.6 mm

Crack height-0.8 mm

Penetration

�Particle penetration factor for

different crack heights

Bin Xu, Shusen Liu, and Yifang Zhu “Ultrafine particle penetration through idealized vehicle cracks”,

2010, Journal of Aerosols Science, 41(9) 859-868.

Key

point

Penetration factors increase as

crack length decreases and

crack height increases.

25

� Experimental Setup: Particle generation and measurements

Deposition

26

�In-cabin air velocity under

various vehicle speeds and

ventilation settings.

Vehicle speed (mph)

10 20 30 40 50 60 70

In-cabin air velocity (m s

-1)

0.0

.1

.2

.3

.4

.5

.6

.7

Fan off RC off

Fan on RC off

Fan on RC on

Deposition

Key

point

In-cabin air velocity

increases as vehicle

speed increases. Fan

off/RC off has the lowest

in-cabin air velocity.

27

The relationship between ln(C/C0) and time

for some specific particle sizes inside the test

vehicle (a) 30 nm (b) 66.1 nm (c) 101.8 nm

The value of the slope is equal to particle

deposition rate and increased with

increasing in-cabin air velocity.

time (min)

0 10 20 30 40 50

ln(C/C

0)

-10

-8

-6

-4

-2

0

natural convencton, Slope=7.64 h-1

V1=0.25 m s

-1, Slope=8.36 h

-1

V2=0.45 m s

-1, Slope=9.76 h

-1

V3=0.65 m s

-1, Slope=11.21 h

-1

(a) 30 nm

time (min)

0 20 40 60 80 100 120 140 160

ln(C/C

0)

-10

-8

-6

-4

-2

0

natural convection, Slope=3.28 h-1

V1=0.25 m s

-1, Slope=3.52 h

-1

V2=0.45 m s

-1, Slope=3.90 h

-1

V3=0.65 m s

-1, Slope=4.05 h

-1

(b) 66.1 nm

time (min)

0 50 100 150 200 250

ln(C/C

0)

-8

-6

-4

-2

0

natural convection, Slope=2.65 h-1

V1=0.25 m s

-1, Slope=2.73 h

-1

V2=0.45 m s

-1, Slope=2.84 h

-1

V3=0.65 m s

-1, Slope=2.97 h

-1

(c) 101.8 nm

Vehicle speed (mph)

10 20 30 40 50 60 70

In-cabin air velocity (m s

-1)

0.0

.1

.2

.3

.4

.5

.6

.7

Fan off RC off

Fan on RC off

Fan on RC on

Deposition

28

Surface area to volume ratio (m-1)

3 4 5 6 7 8 9 10

Particle deposition rate (h-1)

2

4

6

8

10

12

14

16

18

30 nm

66.1 nm

101.8 nm

Isuzu Rodeo SUV

Satrun SL2 car

The particle deposition rates as a function of surface area to volume

ratios for 30, 66.1, and 101.8 nm particles inside two test vehicles.

Deposition

Longwen Gong, Bin Xu and Yifang Zhu “Ultrafine Particles Deposition inside Passenger Vehicles", 2009, Aerosol Science

and Technology, 43: 544-553.

Key

point

There is a positive correlation between surface area to

volume ratios and ultrafine particle deposition rates.

Greater surface area to volume ratio results in higher

deposition rate for ultrafine particles.

29

DMA CPC

SMPSAir flow meter

Diesel

Generator

Fan

Filter

�Ultrafine Particle Filtration Efficiency Measurements

ionconcentratupstream

ionconcentratdownstreamEfficiencyFiltration −= 1

Filtration

30

�Coarse Particle Filtration Efficiency Measurements

Filtration

Particle diameter, nm

10 100 1000 10000

Filtration efficiency

0.0

0.2

0.4

0.6

0.8

1.0

Filter A

Filter B

Filter C

Xu, Liu, Liu, and Zhu, 2010 ‘Effects of cabin filter on in-cabin to on-roadway ultrafine particle ratios’

Aerosol Science and Technology, Aerosol Science and Technology, 45:215–224.

Cabin Filter Performance: The Good, the Bad, and the Ugly

Filtration

32

Particle diameter, nm(a)

10 100 1000 10000

Filtration efficiency

0.0

0.2

0.4

0.6

0.8

1.0

0.1 m s-1

0.3 m s-1

0.5 m s-1

Particle diameter, nm(b)

10 100 1000 10000

Filtration efficiency

0.0

0.2

0.4

0.6

0.8

1.0

0.1 m s-1

0.3 m s-1

0.5 m s-1

Particle filtration efficiencies as a function of particle size under

various filter face velocities

Filtration

Filter A Filter B

Xu, Liu, Liu, and Zhu, 2010 ‘Effects of cabin filter on in-cabin to on-roadway ultrafine particle ratios’

Aerosol Science and Technology, Aerosol Science and Technology, 45:215–224.

Percent particle reduction (%)

0 20 40 60 80 100

No Filter: 01 HondaNo Filter: 05 ToyotaNo Filter: 04 ToyotaNo Filter: 08 ToyotaNo Filter: 10 Honda

In-use w/o sealing: 01 HondaIn-use w/o sealing: 05 ToyotaIn-use w/o sealing: 04 ToyotaIn-use w/o sealing: 08 ToyotaIn-use w/o sealing: 10 HondaIn-use w/ sealing: 01 HondaIn-use w/ sealing: 05 ToyotaIn-use w/ sealing: 04 ToyotaIn-use w/ sealing: 08 ToyotaIn-use w/ sealing: 10 HondaNew Commercial: 01 HondaNew Commercial: 05 ToyotaNew Commercial: 04 ToyotaNew Commercial: 08 ToyotaNew Commercial: 10 Honda

HEPA: 01 HondaHEPA: 05 ToyotaHEPA: 04 ToyotaHEPA: 08 ToyotaHEPA: 10 Honda

33

HEPA filter

New

commercial

In-use sealing

In-use no

sealing

No filter

Filtration

Key

point

In-cabin filtration has great potential to significantly

reduce commuters’ exposure to ultrafine particles while at

the same time solve the CO2 build up problem.

34

Time

06:35 07:05 07:35 08:05

Total particle number concentration (#/cm3)

0.0

5.0e+3

1.0e+4

1.5e+4

2.0e+4

2.5e+4

3.0e+4

3.5e+4

4.0e+4

(1) (5)(2) (3) (4)

(5) Town route

(2) Bus transfer station

(3) Line-up with other

school buses leaving

the transfer station

(4) School parking lot

Effect of route

(1) Rural route

School Bus Test

Time

15:45 15:46 15:47 15:48 15:49 15:50 15:51 15:52

Particle number concentration (#/cm

3)

0.0

1.0e+4

2.0e+4

3.0e+4

4.0e+4

Starting-up IdlingDriving

35

Effect of operation

School Bus Test

36

Time

06:50 07:10 07:30 07:50 08:10 08:30

Total particles (#/cm

3)

0

5000

10000

15000

20000

25000

I/O ratio

0.0

.2

.4

.6

.8

1.0

In-cabin particles

Ambient particles

I/O ratio

Air Purifiers OffOne Air

Purifier OnTwo Air

Purifiers On Air Purifiers Off

I/O=0.82

I/O=0.40

I/O=0.55

I/O=0.83

School Bus Filtration

37

I/O ratio inside school buses without/with air purifiers

Zhang and Zhu 2011 “Performance of School Bus Retrofit Systems: Ultrafine Particles and Other Vehicular Pollutants”, 2011,

Environmental Science and Technology, 45: 6475–6482.

School Bus Filtration

Key

point

Stand-along air purifiers can significantly reduce

particulate matter (PM2.5 and ultrafine particle) levels

inside vehicles.

Reducing UFP Exposure Near Roadways:

- Meteorology: stay on the upwind side of major roadways;

- Spatial Profile: stay away from major roadways;

- Temporal Profile: avoid heavy traffic hours

Summary

Reducing UFP Exposure inside Vehicles:

- Route: avoid heavy-duty vehicle route

- Driving: avoid idling

- In-Cabin Ventilation : close window and turn on recirculation

- In-Cabin Filtration: use HEPA filter/air purifier

Co-Authors: William C. Hinds, Constantinos Sioutas, Seongheon Kim, Si Shen, Margaret Krudysz, Thomas Kuhn, John F. Froines, Paul Mayo, Arantza Eiguren-Fernandez, Antonio H. Miguel, Longwen Gong, Bin Xu, Shusen Liu, and Qunfang Zhang.

SupportSupportSupportSupport

Health Effects Institute (HEI)

National Science Foundation (NSF)

California Air Resource Board (CARB)

US Environmental Protection Agency (EPA)

Acknowledgements