Atmospheric chemistry

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Atmospheric chemistry

• Day 5
• Ozone and air quality
• Air quality and climate change

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Impact of air pollutionUK 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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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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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.
• Urban chemistry high concentrations of NO from
  transport sources. Ozone is depressed by the
  reaction
• NO O3 ? NO2 O2

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Ozone mixing ratios at MaceHeadW. Ireland, under
westerly airflows
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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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Radiative Forcing

• Radiative forcing the change in the net
  radiation balance at the tropopause caused by a
  particular external factor in the absence of any
  climate feedbacks.
• These forcing mechanisms can be caused by
• change in the atmospheric constituents such as
  the increase in greenhouse gases (GHGs)
• aerosols due to anthropogenic activity,
• changes in other components of the
  Earth/atmosphere system such as changes in the
  surface albedo (the fraction of incoming
  radiation that is reflected). Albedo changes are
  caused, e.g., by changesin vegetation (e.g. burn
  scars or agriculture).

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Mechanisms of the radiative forcingdue to
greenhouse gases and of the direct radiative
forcings due to aerosols
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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
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Carbon dioxide and methane mixing ratios versus
time (NOAA Climate Monitoring and Diagnostics
Laboratoryhttp//www.cmdl.noaa.gov/ccgg/insitu.ht
ml)
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Other GHGs

• N2O mixing ratios show an increase from a
  pre-industrial value of around 270 ppb (Prather
  et al., 2001) to 318 319 ppb in early 2004
• CFC-11, CFC-12, CFC-13, HCFC-22, and CCl4
  concentrations increased from a pre-industrial
  value of zero to 268 ppt, 533 ppt, 4 ppt, 132
  ppt, and 102 ppt respectively (1998
  concentrations) - leads to radiative forcings of
  0.07 W m-2, 0.17 W m-2, 0.03 W m-2, 0.03 W m-2
  and 0.01 W m-2
• Ozone approximate doubling of concentrations
  between the pre-industrial and present day.

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Climate System
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Schematic description of an ocean atmosphere
general circulation model
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Evolution of models
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Carbon cycle
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Processes in an atmospheric chemistry model
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Sulfur cycle
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Sulfur emissions
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Sulfur emissions 1860 - 1990
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UK 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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Global NOx and CH4 emissions scenarios
NOx
CH4
CLE - current legislation SRES IPCC
analyses MFR maximum feasible reduction
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SRES (IPCC Special Report on Emission Scenarios)
scenarios

• The A1 storyline is for a future world with very
  rapid economic growth, global population that
  peaks in mid-century and declines thereafter, the
  rapid introduction of new and more efficient
  technologies and with a substantial reduction in
  regional differences in per capita income.
  Within this family are three sub-scenarios with
  different technological emphasis
• A1FI A1, fossil fuel intensive
• A1T A1, with non-fossil energy source emphasis
• A1B A1, with a balance across energy sources.
• The A2 storyline is a more pessimistic scenario,
  describing a very heterogeneous world based on
  self-reliance, regional differences in economic
  and technological development and continuous
  increase in global population.
• The B1 storyline describes a convergent world
  like A1, with global population peaking in
  mid-century, but with rapid changes in economic
  structures, introduction of clean and
  resource-efficient technologies, emphasis on
  global solutions to social and environmental
  sustainability.
• The B2 storyline describes a world with emphasis
  on local solutions to social and environmental
  sustainability, less rapid and more diverse than
  in B1 and A1, with continuously increasing global
  population, but at a lower rate than A2.

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Royal Society Report on ozone over next 100
yearsLevel of automobile emission limits in
Asian countries, compared with the EuropeanUnion.
Source Clean Air Initiative for Asian cities
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Impact of improved technologies in Asian
countries on assessment of NOx emissions
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New estimates of CO emissions
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New estimates of CH4 emissions
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Predicted lobal temperature rise for different
scenarios
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Surface O3 (ppbv) 1990s
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Change in surface O3, CLE 2020s-1990s No climate
change
CLE
A large fraction is due to ship NOx
BAU
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?O3 from climate change
2020s CLEcc- 2020s CLE
Warmer temperatures higher humidities increase
O3destruction over the oceans
O3 hn? O1D O2 O1D H2O ? 2OH O1D N2, O2 ?
O3P
But also a role from increases in isoprene
emissions from vegetation changes in lightning
NOx
OHRH(O2) ? RO2 H2O RO2 NO ?RO NO2 NO2
hn(O2)?NOO3
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Atmospheric oxidation of methane
O1D H2O? 2OH O1D N2,O2? O3P ?
O3
Yield of OH and loss of O3 depend on humidity
CH4 removed mainly by reaction with OH
High NOx route Ozone formation Polluted atmos
Low NOx route Ozone destruction (background atmos)
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PAN peroxy acetyl nitrate
PAN is formed from reactions of the acetyl peroxy
radical and NO2 e.g. CH3CHO OH (O2) ? CH3COO2
H2O CH3COO2 NO2 CH3COO2NO2 (PAN)

• PAN is a reservoir compound for nitrogen oxides
  and provides a mechanism for their transport,
  especially in the upper troposphere. It provides
  a means of carrying nitrogen oxides from polluted
  to less polluted regions. It is a major player in
  the intercontinental transport of pollutants

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Impact of climate change on air quality - ozone
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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.
• What about Hungary?
• How frequent will such summers be in the future?

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Budapest, 1 31 August 2003
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NO2 in Budapest and Hungary in 2005
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Diurnal variation
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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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Emission of biomass smoke from Portugal in August
2003 effects on local albedo