Attaining urban air quality objectives- links to transboundary air pollution

Helen ApSimon, Tim Oxley and Marios Valiantis

UK Centre for Integrated Assessment Modelling

Imperial College London

SOURCES EMISSION EXPOSURE EFFECTS/RECEPTORS

Energy

Agriculture

Industry

Traffic

Sulphur dioxide

Ammonia

Nitrogen oxides

VOCs

Sulphur deposition

Nitrogen deposition

SO2,SO4 air concns

NO2,NO3 air concns

Ozone

Acidification

Eutrophication

Human health

Materials

Yield losses

Surface waters

Terrestial ecosystems

Marine ecosystems

Crops

Forests

Domestic

Particles PM10/2.5

NH4 concn

CO2

N2O

CH4

C

L

I

M

A

T

E

AIR QUALITY

NO2

Particulate matter

PM10: Limit values (max. conc at hot-spots)

Annual mean conc. 40g.m-3

24 hr conc 50 g.m -3 < 35 days per year

Targets proposed for PM2.5

Limit values 25 g.m -3

and “exposure reduction”: 20% at urban background sites

BENEFITS e.g. in UK 2005 baseline-> £9 to £21 bn/y for life years lost (DEFRA: Air Quality Strategy for England, Scotland, Wales and N Ireland- consultation document April 2006)

NITROGEN DIOXIDE

Limit values:

Annual mean conc. 40 g.m -3 (21 ppb)

I hr mean 200 g.m -3 (105 ppb) <18 times /yr

Wide-spread exceedence in European cities, especially at road-side sites.

Adds to importance of reducing NOx, but emphasizes urban sources, particularly traffic

Illustrate other links to CLRTAP

ASAM- European scale (50km)

UKIAM- UK scale (5km)

BRUTAL- Background Road & Urban Transport modelling of Air quality Limit Values->

Superimpose road-side on background

Road network + traffic data-> traffic emissions individual roads and gridded

Pop. Data -> urban areas/roads (canyons etc)

Modelled background concentrations:-

First model NOx using same model, PPM, used for primary PM .

Then convert to NO2 using relationship between NO2 and NOx

NB Good agreement with measurements , but requires added rural background

Background NOx inferred from rural diffusion tube network

->10 g.m -3 most of England

Preliminary calculations suggest that imported NOx contributes to this background including shipping- so some transboundary component. Applies to other countries too?

EMEP source apportionment: relative importance of transboundary and own country:

NOx/ NO2 conc. not given by EMEP, but probably more like reduced N deposition and PMcoarse?

SCENARIO ANALYSIS

Superimpose roads:

Traffic emissions: traffic flows and vehicle mix combined with speed-dependent emission factors (individual roads and summed over grid square)

Scenarios:

Tech. measures e.g. EGR, early introduction Euro V,VI ; hybrids/LEVs

Local measures/ reduced traffic volumes: congestion zones; :LEZs etc.

PRELIMINARY RESULTS

Projections of NO2 for 2010 at road-side sites: contributions from roads superimposed in each 1x 1 km grid square on top of background-> mapping of peak concns at hot-spots

BAU

LEZ

Max. tech. reduction case

+ factors ~CLRTAP

-> section across London

BRUTAL (15.5.06): Scenario transects across London for peak NO2 at road-side sites in each grid-cell

Changes in NO2/NOx relationships

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

NOx X 10 ppb

NO2 base

20% prim NO2

5ppb more O3

NO2 secondary- NO2 primary fraction- evidence

depends on O3 of increase - PMtraps

Example: 50 ppb NOx -> 25 ppb NO2 (limit value 21 ppb)

Reduce to 35 ppb NOx-> 20 ppb NO2 (OK). BUT!

5 to 20% prim. frac-> 22 ppb NO2; plus more O3 -> 23ppbNO2 (not OK)

NO2 ppb

Similar analysis PM10

e.g. benefits of PM traps

NB importance of non-exhaust emissions- brakes/tyres

Summary: links UAQ and CLRTAP

1.Local control of urban air quality puts extra emphasis on traffic emissions detailed modelling of scenarios

2. High economic benefits(PM)

3. Some direct transboundary contribution to NOx/NO2 ?

4. NO2-NOx ratios dependent on ozone NB background ozone increasing

5. Interaction other pollutants- PM trap-> increased primary NO2.