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Regulatory and Air Quality Implications of Setting Particle
Number Standards
Roy M. HarrisonUniversity of Birmingham and
National Centre for Atmospheric Science
CONTENT
• Particle size distributions and the meaning of particle number concentration
• Sources and environmental behaviour of nanoparticles
• Epidemiology of nanoparticle exposures
• Conclusions
Particles of < 100 nm diameter are very numerous in the
atmosphere but have very little mass
NANOPARTICLES
NANOPARTICLESInfluence of Particle Size on Particle Number and Surface Area
for a Given Particle Mass
RELATIVE PARTICLE NUMBER OF RELATIVE DIAMETER PARTICLES SURFACE AREA
10 µm 1 1
1 µm 103 102
0.1 µm 106 104
0.01 µm 109 106
PARTICLE SIZEDISTRIBUTIONMEASURED IN BIRMINGHAM
Particle Size Distributions at Marylebone Road
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
10 100 1000
Night
Morning rush hour
Midday
Afternoon rush hour
28 nm
30 nm
32 nm
26 nm
dN/d
logD
P cm
-3
Particle Diameter (nm)
Particle Number, Surface Area and Mass
Measuring:Particle number reflects particles < 100
nanometres primarily
Particle surface area reflects mainly particles of 50-1000 nm
Particle mass reflects particles of > 100 nanometres (usually to 2.5 µm or 10 µm)
UK PM0.1 Emissions 1970-2008
MERGING SIZE DISTRIBUTIONS AND ELUCIDATION OF
PARTICLE SOURCES
MEAN MERGED SMPS-APS SPECTRA
CRAN – R GUI
• REPARTEE II data from the Marylebone Road.
• October 2007.
• SMPS TSI 3080 Classifier and TSI 3776 CPC• APS TSI 3321
An Enhanced Procedure for the Merging of Atmospheric Particle Size Distribution Data Measured Using Electrical Mobility and Time-of-Flight Analysers, D.C. Beddows, M. Dall’Osto and R.M. Harrison, Aerosol Sci. Technol., 44, 930-938 (2010).
NUMBER FACTORS AND SCORESMean Concentration (%)
Volume Number
Marylebone Road Emissions
Exhaust - solid mode (factor 3)
Exhaust - nucleation mode (factor 4)
18.8
3.6
38.0
27.4
Solid carbonaceous mode
Diurnal Traffic pattern
Strong LDV association
Morning rush hour
Nucleation mode from dilution of diesel exhaust
Mean Concentration (%)
Volume Number
Marylebone Road Emissions
Exhaust - solid mode (factor 3)
Exhaust - nucleation mode (factor 4)
Brake dust (factor 2)
Resuspension (factor 7)
Sub-total
18.8
3.6
13.7
4.4
40.5
38.0
27.4
1.7
4.8
71.9
Urban Background
Accumulation mode (factor 1)
Suburban traffic (factor 5)
Nitrate (factor 6)
Regional (factor 8)
Cooking (factor 9)
Regional (factor 10)
Sub-total
12.8
2.3
8.4
2.5
6.7
26.8
59.5
6.3
7.6
2.0
2.7
6.6
3.0
28.2
Attribution of mean particle volume and number to tentatively assigned sources
TAKE-HOME MESSAGE
Vehicle exhaust nanoparticles comprise two types:• nucleation mode – mainly condensed
lubricating oil, centred on 20 nm diameter• solid mode – graphitic carbon – centred on
50-60 nm diameter
PMF Analysis of Wide-Range Particle Size Spectra Collected on a Major Highway, R.M. Harrison, D.C.S. Beddows and M. Dall’Osto, Environ. Sci. Technol., 45, 5522-5528 (2011).
THE REPARTEE EXPERIMENT
Atmospheric Chemistry and Physics in the Atmosphere of a Developed Megacity (London): An Overview of the REPARTEE Experiment and its Conclusions, R.M. Harrison, M. Dall’Osto, D.C.S. Beddows, A.J. Thorpe, W.J. Bloss, J.D. Allan, H. Coe, J.R. Dorsey, M. Gallagher, C. Martin, J. Whitehead, P.I. Williams, R.L. Jones, J.M. Langridge, A.K. Benton, S.M. Ball, B. Langford, C.N. Hewitt, B. Davison , D. Martin, K. Petersson, S.J. Henshaw, I.R. White, D.E. Shallcross, J.F. Barlow, T. Dunbar, F. Davies, E. Nemitz, G.J. Phillips, C. Helfter, C.F. Di Marco and S. Smith, Atmos. Phys. Chem., 12, 3065-3114 (2012).
Map of Central London
60x103
50
40
30
20
10
0
d N
/ d
Lo
g D
p
4 5 6 7 8 910
2 3 4 5 6 7 8 9100
2 3 4 5 6 7 8 91000
Da [ m ]
MR_12
DMPS_12
c
Park Road Tower
Remarkable dynamics of nanoparticle in the urban atmosphere
• The typical size distribution measured at the Road site peaking between 20 and 30 nm diameter.
• In contrast, data from the Park site showed a mode which had shifted downwards to below 10 nm diameter.
• There is almost complete loss of the sub-30 nanometre mode at the BT Tower site.
D [nm]
40x103
30
20
10
0d N
/ d
lo
g D
p
2 3 4 5 6 710
2 3 4 5 6 7100
2 3 4 5 6 71000
mobility diameter (m)
20x103
15
10
5
0
60x103
40
20
0
Road
Park
Tower
On distance scales of the order of 1 km and travel times of around 5 minutes upon moving away from major emissions sources very significant loss of the nanoparticle fraction is observed which manifests itself in a shift to smaller sizes within Regents Park and an almost complete loss of the sub-30 nanometre mode at the BT Tower site.
mobility diameter [nm]
TAKE-HOME MESSAGE
• The nucleation mode particles in traffic exhaust are semi-volatile and evaporate as they are carried downwind of source, or mixed upward in the atmosphere
Remarkable Dynamics of Nanoparticles in the Urban Atmosphere, M. Dall’Osto, A. Thorpe, D.C.S. Beddows, R.M. Harrison, J.F. Barlow, T. Dunbar, P.I. Williams and H. Coe, Atmos. Chem. Phys., 11, 6623-6637 (2011).
Particle Nucleation
• New particle formation in the atmosphere can lead to huge bursts of nanoparticle concentration
• Highly prevalent in southern Europe, but less so in the UK
• Health impacts of particles formed by regional nucleation are not known
New Considerations for PM, Black Carbon and Particle Number Concentration for Air Quality Monitoring Across Different European Cities, C. Reche, X. Querol, A. Alastuey, M. Viana, J. Pey, T. Moreno, S. Rodriguez, Y. Gonzalez, R. Fernandez-Camacho, A.M. Sanchez de la Campa, J. de la Rosa, M. Dall’Osto, A.S.H. Prevot, C. Hueglin, R.M. Harrison and P. Quincey, Atmos. Chem. Phys., 11, 6207-6227 (2011).
BIRMINGHAM, JUNE 1999
Contrasting Behaviour of PM Mass and PM Number
If there were a temporary cessation of PM emissions and secondary formation:• Particle mass would be conserved and diminish only
slowly due to deposition processes• Particle number would not be conserved. It would
diminish due to:- evaporation- coagulation- surface deposition
Or, might increase due to nucleation!
TEMPORAL TRENDS IN PARTICLE NUMBER CONCENTRATIONS
0 50 100 150 200 250 300 350 400 450 5000
20000
40000
60000
80000
100000
120000
140000
Marylebone Road: Number v NOx at 100 wind sectors
Oct 05 - Sep 07
Feb 08 - Jan 09
NOx (as NO2) [µg m-3]
Parti
cle
num
ber [
cm-3
]
TAKE-HOME MESSAGE
• Nanoparticle concentrations have fallen sharply since late 2007, especially at roadside sites
• The cause is most probably the transition to “sulphur-free” diesel fuel
A Large Reduction in Airborne Particle Number Concentrations at the time of the Introduction of “Sulphur Free” Diesel and the London Low Emission Zone, A.M. Jones, R.M. Harrison, G. Fuller and B. Barratt, Atmos. Environ., 50, 129-138 (2012).
Richard Atkinson and Ross Anderson (St. George’s Hospital Medical School) used case-crossover time series methodology to estimate the percentage increase in a given health outcome corresponding to the inter-quartile range (75%ile minus 25%ile) of concentration for several particle metrics
London Epidemiological Study
Urban Ambient Particle Metrics and Health: A Time Series Analysis, R.W. Atkinson, G.W. Fuller, H.R. Anderson, R.M. Harrison and B. Armstrong, Epidemiology, 21, 501-511 (2010).
Cardiovascular Mortality (lag 1)(Graph shows % change between 25%ile
and 75%ile concentration and 95% CI)
-20
24
6%
(95
% C
I)
PNCNO3 CL
SO4 BS
GR PM
10
NK PM
10
PM10
GR PM
25
PM25
GR PM
102.
5
PRI10
NONP10
NONP2.5
NONP102.
5
-20
24
6%
(95
% C
I)
PNCNO3 CL
SO4 BS
GR PM
10
NK PM
10
PM10
GR PM
25
PM25
GR PM
102.
5
PRI10
NONP10
NONP2.5
NONP102.
5
Respiratory Mortality (lag 2)(Graph shows % change between 25%ile
and 75%ile concentration and 95% CI)
-20
24
68
% (
95%
CI)
PNCNO3 CL
SO4 BS
GR PM
10
NK PM
10
PM10
GR PM
25
PM25
GR PM
102.
5
PRI10
NONP10
NONP2.5
NONP102.
5
-20
24
68
% (
95%
CI)
PNCNO3 CL
SO4 BS
GR PM
10
NK PM
10
PM10
GR PM
25
PM25
GR PM
102.
5
PRI10
NONP10
NONP2.5
NONP102.
5
Desktop Study of Nanoparticles from Traffic in DelhiPrashant Kumar and co-workers examined particle number emissions in Delhi and three scenarios: Present day (2010) Business as usual (2030) Best estimate scenario (2030)
Impacts on mortality were estimated using two sources of exposure-response functions: Atkinson et al. (2010) Stolzel et al. (2007)
Preliminary Estimates of Nanoparticle Number Emissions from Road Vehicles in Megacity Delhi and Associated Health Impacts, P. Kumar, B.R. Gurjar, A.K Nagpure and R.M. Harrison, Environ. Sci. & Technol., 45, 5514-5521 (2011).
Estimated excess deaths annually in Delhi for different air quality scenarios and exposure response functions – central estimate and 95% confidence intervals
Excess deaths are derived from the ambient ToN concentrations (after losses) and figures in parentheses are 95% CI values
Note: Based solely on acute effects as chronic effects of UFP exposure are not known
CONCLUSIONS
• It would be possible to use the results of studies such as Atkinson et al. (2010) and Stolzel et al. (2007) to set air quality standards for (traffic generated) particles by number.
• The differential toxicity of ultrafine particles from different sources is not known.
• Nanoparticles behave less conservatively in the atmosphere relative to the larger particles which comprise most of the particle mass, making the relationship between abatement measures and airborne concentrations more difficult to define.
• It is difficult to know whether an AAQS for particle number would offer additional protection of public health relative to the present PM mass standards.
ACKNOWLEDGEMENTS
Dr Alan Jones )Dr Manuel Dall’Osto ) University of BirminghamDr David Beddows )Dr Krystal Godri )
Dr Richard Atkinson ) St. George’sProfessor Ross Anderson )
Dr Gary Fuller ) Kings College, LondonDr Ben Barratt )
Dr Prashant Kumar ) University of Surrey
THANK YOU