A Simple Model for Regional Near-Surface HOx

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A Simple Model for Regional Near-Surface HOx

• Zhijun Zhao
• 2005.4

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Outline

• Introduction
• Model Description
• Model Results
• Model Discussion
• Conclusion

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Introduction

• HOxOHHO2(H)
• most important radicals in atmosphere
• -- OH main oxidant in atmosphere
• -- HO2 OH reservoir and O3 precursor in
  troposphere

D. Tan, et al, 2001
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Introduction

• Measurement of HOx
• only available in recent years
• still very difficult

Average diurnal profile of HOx and j(O1D) in
Ireland, April-May 1997, EASE97 compaign, D.J.
Creasey, et al, 2002
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Model Description

• 24-hour dimensionless box model with time step of
  1 hour.
• Assumption
• -horizontally homogeneous, no transport
• -meteorological parameters constant
• -actinic flux is constant vertically but vary
  with time

Actinic Factor A
Photolysis rate constant jj0A
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Model Description

• Shell structure of species
• --Fixed and varied
• --Steady state and non-steady state

Varied species are indicated in bold font. a
Species with short lifetime to be treated as
steady state b Species treated as steady state in
the day but non-steady state at night c NOx is
fixed but NO/NO2 is varied
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Model Description

• Chemical reaction types
• Photolysis reaction j
• Bimolecular reaction bk
• Termolecular reaction tk
• Equilibrium reaction ek
• Heterogeneous reaction hk

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Model Description

• Numerical solution of chemical equation

Steady state Non-steady state
The sensitivity of the 1-hour time step is also
checked.
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Model Results

• Typical temporal profile of HOx and HO2/OH
• NOx21011,CH421013,O311011
• Temporal profile of HOx and HO2/OH in different
  CH4 concentration
• NOx21011,O311011

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Model Results

• Temporal profile of HOx and HO2/OH in different
  NOx concentration
• CH421013,O311011

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Model Results

• Temporal profile of HOx and HO2/OH in different
  O3 concentration
• NOx21011,CH421013

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Model Discussion

• The results show a positive dependence of HOx and
  HO2/OH on the CH4 and O3 concentration and a
  negative dependence on NOx concentration during
  the daytime but not sensitive at night.

Stevens, et al, 1997
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Model Discussion

• NO/NO2 ratio in daytime and at night

In daytime the concentration of NO and NO2 have
the almost same order of magnitude. At night NO2
dominant NOx while NO is much less.
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Model Discussion

• Observation value of HO2/OH 101000
• -- NOx dependence
• -- Neglecting other hydrocarbons, such as
  isoprene

D.J. Creasey, et al, 2002
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Conclusion

• A regional box model is set up, which could be
  applied to a polluted area, e.g. downtown
  Atlanta.
• In the daytime, the near surface HOx and HO2/OH
  both have a positive dependence on CH4 and O3,
  and a strong negative dependence on NOx.
• At night, the HOx and HO2/OH are both much less
  sensitive to CH4, NOx and O3 without the sunlight
  radiation.
• There are still some disagreements with the
  observation values.

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Thank You! Any Question?