Quantifying the chemical indirect effect of aerosols on climate

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Quantifying the chemical indirect effect of
aerosols on climate
School of Earth and Environment FACULTY OF
ENVIRONMENT

• Helen Macintyre1, supervisors Mat Evans1, Ken
  Carslaw1 and Colin Johnson2.

1. University of Leeds 2. Met Office
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School of Earth and Environment FACULTY OF
ENVIRONMENT
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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Aerosol direct and indirect effects

N2O5
HNO3
aerosol
HO2
H2O2
Direct effect
Chemical indirect effect
Indirect effect
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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Chemistry.
• Ozone and methane are important ozone is a
  precursor to OH methane is important green-house
  gas, and its main removal path is oxidation by OH
• NOx (oxides of nitrogen) involved with ozone
  cycle
• HOx (OH, HO2) also linked
• Thus it is important to understand the sources
  and sinks of NOx and HOx

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School of Earth and Environment FACULTY OF
ENVIRONMENT
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School of Earth and Environment FACULTY OF
ENVIRONMENT
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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Uptake coefficient, ?.
• Gamma (?) - reaction uptake coefficient the
  probability that a molecule impacting an aerosol
  surface undergoes reaction (useful to find)
• ? depends on temperature, relative humidity,
  aerosol type, etc.
• Lab studies constrain the value of ?, and we can
  use this information to investigate heterogeneous
  chemistry of NOx and HOx on aerosols, and assess
  the subsequent impact on climate

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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Literature.
• Early models included N2O5 uptake with single
  value (Dentener Crutzen, 1993). Improved
  agreement between observed and modelled wet
  deposition patterns heterogeneous chemistry is
  important
• New lab data available (Kane et al. 2001,
  Thornton et al. 2003, Hallquist et al. 2003) for
  ?N2O5 for a range of temperatures, humidities and
  compositions
• Evans and Jacob, 2005, use these in GEOS-Chem
  (Goddard Earth Observing System) to assess the
  impact of new ? values on NOx, OH and O3

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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Found global mean ? of 0.02 much lower than 0.1
  as previously recommended
• Overall changes NOx 7 higher, O3 4 higher, OH
  8 higher
• Lack of data for organic coated aerosols and
  uptake on mineral dust

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School of Earth and Environment FACULTY OF
ENVIRONMENT

• New studies.
• New information on uptake by mineral dust (Mogili
  et al., 2006 Karagulian et al., 2006)
• Information on organic coatings on sulphate
  aerosol (Badger et al., 2006)
• Nitrate effect aerosol containing large amounts
  of nitrate have a lower ? value than those
  without (Wahner et al., 1998 Mentel et al.,
  1999)

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School of Earth and Environment FACULTY OF
ENVIRONMENT
New dust values.
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School of Earth and Environment FACULTY OF
ENVIRONMENT
Sulphate aerosol containing 10 wt organics
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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Next steps.
• Refine organic coatings (so far done only for
  sulphate as there is only literature available
  for this)
• Yearly runs
• Finalise HO2 uptake
• Run in UKCA (UK Chemistry Aerosol model)
• Assess the impact on radiative forcing

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School of Earth and Environment FACULTY OF
ENVIRONMENT

• Thank you.
• h.macintyre_at_see.leeds.ac.uk