South Coast Air Quality Management District
Ultrafine Particle Conference
April 30 – May 2, 2006
Understanding the Potential Ultrafine
Particle Pollution Problem and its Impact
on California’s Air Quality
Robert Sawyer, PhD
Chair
California Air Resources Board
Ultrafine particle toxicology is a
research priority
Combustion-generated ultrafine particle
emissions is a research priority for CARB as
some research evidence suggests that ultrafine
particles may be important in the inducement of
adverse health effects, but the toxicology of
ultrafine particles is remains poorly understood.
Until the science of ultrafine particle toxicology
gives better guidance, we will continue to use
particle mass as the best indicator of PM related
adverse health effects.
Intriguing health-related findings
Ultrafines
• Create greater inflammatory response than
fine PM
• Affect heart rate variability
• Are more potent in inducing cellular damage
than fine PM
• May be associated with premature death
Why are ultrafine particles harmful?
Little mass, but:
● Possess large surface area and numbers
● Contain toxic components (e.g. metals,
organics)
● Initiate harmful oxidant injury in lung
● Have high deposition rate in the lung
● Can access circulatory system and move
from lungs to other organs
Particle size and composition:
relation to toxicity
Coarse
Size
Organic carbon content
Elemental carbon content
Metals as % of total elements
PAH content
Redox activity (DTT assay)
HO-1 induction
GSH depletion
Mitochondrial damage
2.5-10 µm
+
+
+++
+
+
+
+
None
Fine
0.15-2.5 µm
++
++
++
+
++
++
+++
Some
Ultrafine
<0.15 µm
+++
+++
+
+++
+++
+++
+++
Extensive
Li et al., CI (2003)
Sources of ambient ultrafine particles
(<100 nm)
Source contributions to primary ultrafine particle emissions in the South Coast Air Basin (1996)
Stationary fuel
use
32.2%
Surface
coating
0.2%
On-Road
vehicles
43.1%
Petroleum
industry
0.5%
Miscellaneous
processes
5.2%
Other
industrual
processes
7.2%
Other mobile
sources
10.4%
Waste burning
1.3%
Primary ultrafine
particle originate
almost exclusively
from combustion
sources.
Cass et al., PTRSL (2000)
Exposure and diurnal variations
Particle
Counts
Particle
Size Distribution
Community and Freeways, Los Angeles
2.5E+05
Exposure to ultrafine particles is
very different on a freeway
dominated by diesel trucks (710),
or by light-duty vehicles (110), and
in the community.
dN/dlogDp
2.0E+05
710
1.5E+05
110
Pasadena
1.0E+05
5.0E+04
0.0E+00
1
Westerdahl and Fruin, AE (2005)
10
100
1000
Particle Diam eter [nm ]
Herner and Kleeman, unpublished
Diurnal Variations in Particle Size Distribution
Bakersfield Jan 04, 2001
40,000
30,000
dN/dlogDp
Diurnal variations of ultrafine
particle concentrations in the
community can be significant. In
the San Joaquin Valley, emissions
from evening wood burning can
greatly increase concentrations.
Night
Day
20,000
10,000
0
1
10
100
Particle Size [nm ]
1000
Freeway traffic impacts
Source: Sioutas with permission
Nanoparticles are removed quickly
“This behavior is best explained by dilution and condensation/evaporation”
Zhang et al., AE (2004)
Application to land-use planning
Air Quality and Land Use Handbook: A Community
Health Perspective (www.arb.ca.gov/ch/landuse.htm)
Zhu et al., AE (2002)
In-vehicle fraction of total exposure
6% of day spent driving can represent up to 50% of our exposures
In-Vehicle,
arterial
In-Vehicle,
freeway
Home, night
Outdoors
Home,
evening
Work
(office bldg)
In-Vehicle,
freeway
Home, night
Home,
evening
Average Time Spent
Work (office
bldg)
In-Vehicle,
arterial
Outdoors
Contribution to Exposure
Fruin, ARB (2004)
Emissions from internal
combustion engines
• Ultrafine particle emissions are not a “dieselonly” problem
• More stringent emission standards will lower
mass
• Control technology for solid particles
• Agreed-upon measurement protocols for
ultrafine particle emissions from vehicles
still emerging
• Nucleation events observed driving on road
New diesel engine standards will
control PM mass emissions
12
NOx
PMx10
10
On-Road Engines
g/bhp-hr
8
6
4
2
20
07
-1
0
20
02
19
98
19
94
19
91
19
88
N
o
C
on
tr
o
l
0
PM mass control does not automatically
imply ultrafine particle number control
Diesel particle filter (DPF) is the
key enabling technology for Diesel PM
emission reduction
Diesel Particulate Filters
Laboratory measurements suggest reduction of
diesel ultrafine particle emissions by traps
Average Size Distribution (minidiluter) - 55mph
No trap
1.E+07
dN/dLogDp, part./cc
Particle number concentration, #/cc
1E+10
With
trap
No trap
1.E+06
1.E+05
With
trap
1.E+04
1E+4
Particle Size, nm
1.E+03
1
10
Uncorrected for dilution
Chatterjee et al., SAE (2002)
100
1000
Particle Diameter, Dp [nm]
Holmen and Ayala, ES&T (2002)
Potential for formation of nuclei mode
particles during “real world” driving
There is concern that the use of DPF
increases the number of nanoparticles.
The contention is that post tail-pipe
sulfuric acid and organic vapors are
now nucleating rather than condensing
onto the removed soot particles.
Burtscher, JAS (2005)
On road measurements behind a CRTequipped diesel truck had a distinctive
nucleation mode. Authors suggests
nucleation will happen after
degreening of catalyzed traps.
Kittelson et al., JAS (in press)
ARB investing heavily in UFP measurement
technology to advance our understanding
Extramural research portfolio on
UF particle studies
6
Millions [$]
5
4
Total Reseach Budget
UF Research
3
2
1
2002
2003
2004
2005
On-going CARB-sponsored research
Health and Exposure
•
•
•
•
•
•
Extension of NIH Cardiovascular Health Study – UCI/USC/UCLA
Cardiovascular effects of fine and ultrafine particles during
freeway travel – UCLA
Ultrafine particles and black carbon at LAX – UCLA
Ultrafine particles in schools and homes – UCB
Spatial distribution of ultrafine particles in community air – USC
Spatial gradients of pollutants in Wilmington using a mobile
monitoring platform – UCLA/CARB staff
Emissions and Control
•
•
Toxicity of emissions from heavy-duty and light-duty vehicles –
USC/UCLA/CARB staff
Evaluation of the European Particle Measurement Program
(PMP) protocol for measuring solid particles – UCR/CARB staff
Final remarks
• Ultrafine particles may be responsible for
adverse health effects distinct from PM2.5
mass, but mechanisms are poorly understood.
• Exposures to ultrafine particles are highest
near combustion sources.
• It is important to ensure that particle counts
are reduced in conjunction with particle mass.
• Understanding of these issues is an important
research priority for CARB.
• The results are important to future air quality
standards and regulatory programs.