Is Urban Air Quality a Problem?

Ian Longley

The air is cleaner than it was,isn’t it?

Effect of controls on coal burning

UK NOx emissions from road transport: 1970-88

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UK PM10 emissions from road transport: 1970-88

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Health effects of NO2 & PM10

• Reduction of 1 g/m3 in PM10 could lead to gain in life expectancy of 0.5 weeks at cost of £1bn+ (IGCB Report to DETR, 2001) .

• Saving to NHS order or £1m p.a.

National Air Quality StrategyObjectives (UK)

Pollutant Concentration Measured as Date to be

achieved by Nitrogen Dioxide 200 g/m3 (105ppb)

not to be exceeded more than 18 times a year

1 hour mean

31 December 2005

40 g/m3 (21ppb) annual mean 31 December 2005 Particles (PM10) 50 g/m3 not to be

exceeded more than 35 times a year

24 hour mean

31 December 2004

40 g/m3 annual mean 31 December 2004

Exceedences allow for unfavourable meteorology

The current state of UK Air QualityDays when air pollution was moderate or higher

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The current state of UK Air Quality

Major determinant of air pollution concentrations is the wind

National / international emission abatement strategies: Engines

standard Year comments

Euro I 1992 3-way catalytic conversion

Euro II 1997

Euro III 2000 On-board diagnostics

Euro IV 2005 Around 40% of new UK cars

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20002005

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UK NOx emissions from road transport: 1990-99

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Currently 30 million vehicles registered in UK

Improvements likely to be offset by rise in traffic by 2020

UK PM10 emissions from road transport: 1990-99

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(Inter)national strategies: Petrol/Diesel

• ULSP/ULSD (<50ppm) available from 2000, all fuel by 2005

• EU consulting on 10ppm S limit• Low Benzene Petrol (also ULSP)• City Diesel (7ppm S, 30% less PM, up to 88%

for buses with particle trap)

(Inter)national strategies: Alternative Fuels: Chemical

• LPG – 25000 on the road in UK (including hybrids), 80% less PM for buses

• CNG – UK has 20 filling stations, 50-90% less PM

• 140 CNG buses operating in France

• Biodiesel• Best options for LDVs in

next 10-20 years

(Inter)national strategies: Alternative Fuels - Others

• Hybrid – petrol/electric:• Toyota Prius & Honda

Insight

• Electric – Peugeot 106, Bristol park & ride buses, Cambridge solar bus

• Fuel cells (from 2010? London trial buses in 2003)

Local Air Quality Management

• Environment Act 1995: Local Authority duty• Create Emission Inventories• Dispersion modelling to predict concentrations

NOW and in 2005• Identify areas where 2005 objectives will NOT

be met.

Air Quality Management Areas, e.g. Greater Manchester

• AQMA declared where 2005 objective for NO2 will NOT be met.

AQMAs: e.g. Croydon

AQMAs

• 3 million live within AQMAs, mostly in Greater London.

• RESULT: most L.A.s report most Objectives WILL be met, EXCEPT NO2 and PM10 in urban areas and near major roads.

• L.A.s must draw up Action Plans for AQMAs.

Action Plan options 1: restrictions

• Low Emission Zone (e.g. central London predicted 16% reduction in NOx, 25% PM10 emissions), also Nottingham, Leicester, York, Bath

• Council vehicle fleets• Congestion charging (London, Durham, Bristol,

Edinburgh, Manchester)• Partial or total road closure• Bus/cycle/HGV/high-occupancy lanes• Parking controls/changes

Action Plan options 2

• Traffic calming• Traffic management (signalling, bollards) • Changing speed limits• Smooth driving styles• Rail and light-rail investment• Bus and park-and-ride investment• Public information and ‘encouragement’

Review & Assessment

• Monitoring: modelling compared to measurements

• Models consistently under-predict for NO2 and PM10 in urban areas, especially densely-built-up areas.

• Models perform badly at predicting PM10.

The problem with PM10

• Fine mode (nm) mostly carbonaceous from exhausts. Main suspect in adverse health effects.

• Coarse mode (m) often crustal. Concentrations related to wind speed and direction. Much harder to control.

• Mass measurements (PM10 ) dominated by coarse mode.

SCAR-4 mean road-side aerosol volume spectrum at 4/5m

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Coarse and ultrafine mass fractions at street level during SCAR-4

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Urban hot-spots

• Personal exposure study showed half of exposure of PM2.5 occurred over 15% of time, mostly when travelling (Rea et al, Jl. Air & Waste Manage. Assoc. vol.51, Sep 2001)

• Epidemiological studies based on monitoring sites – R&A shows under-estimate exposure (Alm et al, Atmos. Env. Vol.35, 2001)

• How far into surroundings does a hot-spot’s effects penetrate?

Urban hot-spots: where are they?

Street Canyon Aerosol Research - SCAR

Particle concentrations and fluxes are dependent upon

• Wind speed,• Wind direction and canyon

assymetry,• Emission strength,• Surface heat emission,• Traffic-modified mean

winds,• Traffic-induced turbulence

(especially in low winds),• Particle size

Conclusions

• Urban air quality improved in 1960s, but traffic growth compromised improvements.

• Technological fixes to engines and fuels delivered big improvements and will do so for next 10 – 20 years, but diminishing returns.

• Suburban and urban background air pollution is marginal – susceptible populations.

• Urban hot-spots probably require further measures which may restrict mobility.

• More research needed (by Atmos Physics post-docs).

But…

• Of 2.9 billion living in cities around the world 2 billion in ‘less developed’ regions (UN,1999); majority of worst polluted cities in Asia

• Vehicle emission control technology is expensive• Cooking and small fires major sources• Many cities are less windy than UK cities• Many cities in arid/semi-arid areas – affected by natural

dusts• 2-5% of all deaths in urban areas caused by air

pollution.• Demand for transport growing much faster than ever

happened in Europe.