The quality of the air we breathe

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The quality of the air we breathe

• Mike Pilling
• School of Chemistry, University of Leeds

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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 9.121.4 billion pa.

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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

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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

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Particulate matter trends in emissions and
measured concentrations (UK)
Black smoke, Lambeth, 1961 - 1997
Primary PM10 emissions sources 1970 2001 (AQEG
PM report)
Annual mean PM10, Urban Background sites
AQEG PM report
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Air quality comparison of trends in pollutants
Relative annual mean concentration (monthly
intervals) selection of monitoring sites in
London.
AQEG PM report
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Analysis of data from 196 sites in UK in 2003
High rural background
Small number of rural sites
Roadside, urban background and rural annual
average PM10 TEOM concentrations in 2003
AQEG PM report
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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

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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 2002
AQEG PM report
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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

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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.

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NO2 EU Limit values

• Hourly mean 200 mg m-3, not to be exceeded more
  than 18 times a year, to be achieved by 31st
  December 2010.
• Annual mean 40 mg m-3, to be achieved by 31st
  December 2010.

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Spatial distribution of NOx emissions in the UK
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Maps of annual mean background NO2 concentrations
UK 2010
UK 2001
Key AQ objective is annual mean of 40 mg m-3 to
be achieved by 2010 (EU Directive)
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Air quality comparison of trends in pollutants
Relative annual mean concentration (monthly
intervals) selection of monitoring sites in
London.
AQEG PM report
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NOx and NO2 emissions in London
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Trends in annual mean NOx and NO2, roadside and
kerbside, 1996 - 2005
NOx, NO2 concentrations Full lines NOx. Dashed
lines NO2

• 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

Ratio NO2 / NOx
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Measured NO2 / NO at a number of sites in
London
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Estimates of f(NO2) based on atmospheric
concentrations of NO and NO2
Marylebone Rd
All London sites
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Similar behaviour across Europe - Paris
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NO2 in Budapest and Hungary in 2005
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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
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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.

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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.

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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.

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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 hn ? H2 CO
• HCHO hn (2O2) ? 2HO2 CO
• Note
• 2 x(NO ? NO2) conversions
• HCHO formation provides a route to radical
  formation.

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General oxidation scheme for VOCs

• O3 h? ? O1D O2
• O1D H2O ? 2OH
• OH RH (O2) ? RO2 H2O
• RO2 NO ? NO2 RO
• RO ?? HO2 (RCHO)
• 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)

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Timescales of ozone chemistry

• Global chemistry. Dominated by NOx CH4
  sunlight. Timescales are long as are transport
  distances.
• 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.
• In cities, there are high concentrations of NO
  from transport sources. Ozone is depressed by the
  reaction
• NO O3 ? NO2 O2

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Sources of ozone in W Ireland
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Ozone mixing ratios at MaceHeadW. Ireland, under
westerly airflows
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Regional production of ozone in Europe
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Local effects Ozone depression due to reaction
with high concentrations of NO in London.
Transect of ozone concentrations
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Heat wave in Europe, August 2003

• Monitoring stations in Europe reporting high band
  concentrations of ozone
• gt15 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?

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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 2004

2003 hottest on record (1860) Probably hottest
since 1500. 15 000 excess deaths in Europe
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Budapest, 1 31 August 2003
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Diurnal variation
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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
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Air Quality and Climate Change

• UK Air Quality Strategy (2007)
• The Governments 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.

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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.

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Acknowledgement

• Air Quality Expert Group