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
06
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