The quality of the air we breathe

Mike Pilling

School of Chemistry, University of Leeds

UK Air Quality Strategy, 2007

“Air pollution is currently estimated to reduce the life expectancy of every person in the UK by an average of 7-8 months. The measures outlined in the strategy could help to reduce the impact on average life expectancy to five months by 2020, and provide a significant step forward in

protecting our environment.”

Defra estimate the health impact of air pollution in 2005 cost £9.1–21.4 billion pa.

Synopsis

1. Particulate matter: trends and origins.

2. NO2: increases in emissions of primary NO2 and its impact on roadside and kerbside concentrations

3. Ozone

4. Air quality and climate change

Particulate matter PM

• categorised on the basis of the size of the particles (e.g. PM2.5 is particles with a diameter of less than 2.5μm).

•comprises wide range of materials (soot, nitrate, sulphate, organic compounds)

•primary particles emitted directly into the atmosphere from combustion sources

•secondary particles formed by chemical reactions in the air.

•derives from both human-made and natural sources (such as sea spray and Saharan dust)

•health effects: inhaled into the thoracic region of the respiratory tract. associated with respiratory and cardiovascular illness

Particulate matter: trends in emissions and measured concentrations (UK)

0

100

200

300

400

500

600

1970 1975 1980 1985 1990 1995 2000

PM

10 e

mis

sio

ns

(k

t)

Public Power Comm.Res.&Instit. Comb. Industrial CombustionProduction Processes Road Transport OtherResuspension

0

5

10

15

20

25

30

35

40

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

PM

10 T

EO

M ,

ug

/m3

Belfast Centre

Birmingham Centre

Bristol Centre

Cardiff Centre

London Bloomsbury

Edinburgh Centre

Leeds Centre

Leicester Centre

Liverpool Centre

Newcastle Centre

Southampton Centre

Swansea

Average

0

20

40

60

80

100

120

140

160

180

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

Bla

ck s

mo

ke ,

ug

/m3

Black smoke, Lambeth,1961 - 1997

Annual mean PM10, Urban Background sites

Primary PM10 emissions sources1970 – 2001 (AQEG: PM report)

AQEG PM report

Air quality – comparison of trends in pollutants

Year

1997 1998 1999 2000 2001 2002 2003 2004

rela

tive

annu

al m

ean

conc

entr

atio

n

0

20

40

60

80

100

120

SO2PM10CONOxNO2

Relative annual mean concentration (monthly intervals): selection of monitoring sites in London.

AQEG PM report

Analysis of data from 196 sites in UK in 2003

0

5

10

15

20

25

30

35

40P

M10

ug

m-3

TE

OM

Annual PM10 TEOM

Average Annual PM10 TEOM

Roadside, urban background and rural annual average PM10 TEOM concentrations in 2003

High ruralbackground

Small number of rural sites

AQEG PM report

Secondary PM

• PM is also formed as a secondary pollutant by chemical reactions in the atmosphere.

• This includes oxidation reactions leading to the formation of secondary PM containing:

• Sulphate

• Nitrate

• Organic compounds

• The chemistry involved is close to that involved in ozone formation and explains why ozone episodes are accompanied by enhanced PM

PM episodes – other sources

Saharan dust: e.g. 2-3 March 2002. Hourly mean of 292 g m-3 at Plymouth. 1-2 events per year in UK. 23 in Spain!

Sea salt aerosol during gales, especially coastal sites but also inland. 1-5 episodes / year.

Biomass burning: Forest fires in Russia, September 2002. Peak hourly concentrations in were reported on the 12th of September in the range from 70 – 125 g m-3. Biomass plumes, W Russia,

4 September 2002AQEG PM report

Air Quality Strategy 2007 - PM

Dual approach:

air quality objective/limit value (backstop objective):

PM2.5: annual mean 25μg m-3 by 2020

Exposure reduction: an objective based on reducing average exposures across the most heavily populated areas of the country:

15 per cent reduction in average concentrations in urban background areas across the UK between 2010 and 2020

NO2; NOx = NO + NO2

All combustion processes in air produce oxides of nitrogen

(NOX).

Road transport is the main source, followed by the electricity supply industry and other industrial and commercial sectors.

NO2 is associated with adverse effects on human health: causes inflammation of the airways. Long term exposure may affect lung function and respiratory symptoms. Also enhances the response to allergens in sensitive individuals.

NO2: EU Limit values

Hourly mean: 200 g m-3, not to be exceeded more than 18 times a year, to be achieved by 31st December 2010.

Annual mean: 40 g m-3, to be achieved by 31st December 2010.

Spatial distribution of NOx emissions in the UK

Maps of annual mean background NO2 concentrations

UK 2001 UK 2010Key AQ objective is annual mean of 40 g m-3 to be achieved by 2010 (EU Directive)

Air quality – comparison of trends in pollutants

Year

1997 1998 1999 2000 2001 2002 2003 2004

rela

tive

annu

al m

ean

conc

entr

atio

n

0

20

40

60

80

100

120

SO2PM10CONOxNO2

Relative annual mean concentration (monthly intervals): selection of monitoring sites in London.

AQEG PM report

NOx and NO2 emissions in London

Trends in annual mean NOx and NO2, roadside and kerbside, 1996 - 2005

• NOx shows downward trend, compatible with improved emissions reduction technologies

• This trend is not reflected in NO2.

• Measured NO2 / NOx ratio generally increases with time.

• Not always the case – e.g. Glasgow

0

50

100

150

200

250

300

350

400

450

1998 1999 2000 2001 2002 2003 2004 2005Year

Con

cent

ratio

n (µ

g m

-3, a

s N

O2)

London Marylebone Road Bury Roadside Glasgow Kerbside

Oxford Centre Roadside London Marylebone Road Bury Roadside

Glasgow Kerbside Oxford Centre Roadside

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1998 1999 2000 2001 2002 2003 2004 2005Year

Am

bien

t NO

2/N

Ox r

atio

London Marylebone Road Bury Roadside

Glasgow Kerbside Oxford Centre Roadside

NOx, NO2 concentrationsFull lines NOx. Dashed lines NO2

Ratio NO2 / NOx

Measured [NO2] / [NO] at a number of sites in London

Roadside and kerbside LAQN data

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

NO

2/N

Ox

rati

o r

ela

tiv

e t

o y

ea

r 2

00

6 =

1

A30

BN1

BY7

CD1

CR2

CR4

CY1

EA2

EN2

GR5

HF1

HI1

HS1

HS4

HV1

HV3

KC2

MY1

RB3

RB4

SK2

TH2

WA4

HG1

All sites

Estimates of f(NO2) based on atmospheric concentrations of NO and NO2

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 20070

10

20

30

f-N

O2

year

1997 1998 1999 2000 2001 2002 2003 2004 20050

5

10

15

20

25

30

est

ima

ted

f-N

O2

year

Marylebone Rd

All London sites

Similar behaviour across Europe - Paris

0

20

40

60

80

100

120

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

An

nu

al m

ean

co

nce

ntr

atio

n N

O2

(ug

m-3

)

0

100

200

300

400

500

600

700

An

nu

al m

ean

co

nce

ntr

atio

n N

Ox

(ug

m-3

, as

NO

2)

NO2 FR0895A Roadside

NO2 FR0335A Roadside

NOx FR0895A Roadside

NOx FR0335A Roadside

NO2 in Budapest and Hungary in 2005

the percentage of urban major road length predicted to be above 40 g m-3 annual mean NO2 in 2010 for different f-NO2 percentages (shown in brackets).

2004 base year (10 - 15%)

2010 (10 - 15%)

2010 (15 - 23%)

2010 (20 - 30%)

2010 (25 - 38%)

2010 (30 - 45%)

London 84% 46% 52% 57% 62% 67%

Rest of England 31% 11% 14% 16% 18% 20%

Scotland 22% 6% 8% 9% 10% 12%

Wales 13% 6% 7% 8% 8% 9%

Northern Ireland 8% 0% 1% 1% 2% 3%

Total 35% 15% 17% 19% 21% 24%

AQEG conclusions on primary NO2

Measured NOx concentrations have declined in line with emission changes but NO2 concentrations have not declined as expected, particularly at the roadside and some sites have shown increases in recent years.

Increases in NO2 / NOx ratios could be due to: • increased penetration of Euro-III diesel vehicles fitted with

oxidation catalysts• Fitting of catalytically regenerative particle traps to buses

Exact interpretation difficult given the observation of increases in the NO2/NOx concentration ratio at only some roadside and kerbside sites outside London. Is London particularly sensitive to direct NO2 emissions, because of its size and emission density? But what about Glasgow?

NB more analysis carried out for the sites in London because of the greater availability of data in London.

Similar increases in NO2 / NOx observed in other European countries.

Ozone

not emitted directly from any human-made source. Arises from chemical reactions between various air pollutants, NOX and Volatile Organic Compounds (VOCs), initiated by strong sunlight.

formation can take place over several hours or days and may have arisen from emissions many hundreds, or even thousands of kilometres away.

can damage airways leading to inflammatory reactions; reduces lung function and increases incidence of respiratory symptoms

causes damage to many plant species leading to loss of yield and quality of crops, damage to forests and impacts on biodiversity.

Air Quality Standards: Ozone

European Union Limit Value: Target of 120μg.m-3 (60 ppb) for an 8 hour mean, not to be exceeded more than 25 times a year averaged over3 years. To be achieved by 31 December 2010.

UK Air Quality Objective: Target of 100μg.m-3 (50 ppb) for an 8 hour mean, not to be exceeded more than 10 times a year. To be achieved by 31 December 2005.

Methane oxidation

CH4 + OH (+O2) CH3O2 + H2O

CH3O2 + NO CH3O + NO2

CH3O + O2 HO2 + HCHO

HO2 + NO OH + NO2

HCHO + OH (+O2) HO2 + CO + H2O

HCHO + h H2 + CO

HCHO + h (+2O2) 2HO2 + CO

Note:

2 x(NO NO2) conversions

HCHO formation provides a route to radical formation.

General oxidation scheme for VOCs

O3 + h O1D + O2

O1D + H2O 2OH

OH + RH (+O2) RO2 + H2O

RO2 + NO NO2 + RO

RO HO2 (+R’CHO)

HO2 + NO OH + NO2

NO2 + h NO + O; O + O2 O3

OVERALL

NOx + VOC + sunlight ozone

The same reactions can also lead to formation of secondary organic aerosol (SOA)

Timescales of ozone chemistry

1. Global chemistry. Dominated by NOx + CH4 + sunlight. Timescales are long as are transport distances.

2. Regional chemistry.

• Many VOCs are emitted, e.g. over Europe. Each has its own lifetime governed by its rate constant for reaction with OH. The timescales of ozone production takes from hours to days. The transport distance for a wind speed of 5 m s-1 and a lifetime of 1 day is ~500 km.

3. In cities, there are high concentrations of NO from transport sources. Ozone is depressed by the reaction:

NO + O3 NO2 + O2

Sources of ozone in W Ireland

0

20

40

60

80

100

12001

/01/

2006

01/0

2/20

06

01/0

3/20

06

01/0

4/20

06

01/0

5/20

06

01/0

6/20

06

01/0

7/20

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01/0

8/20

06

01/0

9/20

06

01/1

0/20

06

01/1

1/20

06

01/1

2/20

06

O3,

ug

/m3

Europe-regional

North America

Asia

Europe-intercontinental

Extra-continental

Stratosphere

Ozone mixing ratios at MaceHeadW. Ireland, under westerly airflows

40

50

60

70

80

90

100

110

01/0

4/19

87

01/0

4/19

88

01/0

4/19

89

01/0

4/19

90

01/0

4/19

91

01/0

4/19

92

01/0

4/19

93

01/0

4/19

94

01/0

4/19

95

01/0

4/19

96

01/0

4/19

97

01/0

4/19

98

01/0

4/19

99

01/0

4/20

00

01/0

4/20

01

01/0

4/20

02

01/0

4/20

03

01/0

4/20

04

01/0

4/20

05

01/0

4/20

06

Mo

nth

ly m

ean

bas

elin

e o

zon

e, u

g/m

3

Regional production of ozone in Europe

Local effects – Ozone depression due to reaction with high concentrations of NO in London. Transect of

ozone concentrations

0

10

20

30

40

50

60

70

465000 475000 485000 495000 505000 515000 525000 535000 545000 555000 565000 575000 585000

Easting

An

nu

al

Me

an

Co

nc

en

tra

tio

n (

in g

m-3

)

PCM 2003 2003 AURN measurements Ascot Rural ADMS-Urban 2003

Heat wave in Europe, August 2003

Monitoring stations in Europe reporting high band concentrations of ozone

>15 000 ‘excess deaths’ in France; 2000 in UK, ~30% from air pollution.

Temperatures exceeded 350C in SE England.

How frequent will such summers be in the future?

Future summer temperatures

Using a climate model simulation with greenhouse gas emissions that follow an IPCC SRES A2 emissions scenario, Hadley Centre predict that more than half of all European summers are likely to be warmer than that of 2003 by the 2040s, and by the 2060s a 2003-type summer would be unusually cool

Stott et al. Nature, December 20042003: hottest on record (1860)Probably hottest since 1500.15 000 excess deaths in Europe

Budapest, 1 – 31 August 2003

0

2040

60

80100

120

140

160180

200

0 100 200 300 400 500 600 700 800

time

ozo

ne

/ m

icro

g/m

3

Széna tér

Baross tér

Pesthidegkút

Kőrakás park

Laborc u.

Diurnal variation

13th August 2003Pesthidegkut

0

50

100

150

200

-1 4 9 14 19 24

time of day

ozo

ne

/ mic

rog

/cm

3

Series1

Global-average radiative forcing (RF) estimates and ranges in 2005(relative to 1750) for anthropogenic GHGs and other important agents and mechanisms

Climate change and air quality

Air Quality and Climate Change

UK Air Quality Strategy (2007)

The Government’s environmental policies will be developed with a consideration of their impact on climate change and greenhouse gas emissions, and this is particularly true of air quality.

Where practicable and sensible, synergistic policies beneficial to both air quality and climate change will be pursued.

Where there are antagonisms, the trade-offs will be quantified and optimal approaches will be adopted.

Examples of difficult issues in assessing impact of emissions on climate change and air quality

• Diesel vehicles:

• Need a more complete assessment of savings of CO2 emissions for diesel vs petrol

• Difficulties of defining metrics for black carbon emissions (absorptive aerosol) for climate change and in assessing the air quality (health) impacts relative to climate change impacts of CO2 reduction.

• Ozone precursors:

• NOx emissions impact on global CH4 and O3, both of which are greenhouse gases. Effects are of opposite sign

• VOC emissions from biofuel crops could enhance episodic ozone, especially as temperatures rise.

Acknowledgement

Air Quality Expert Group