Some important Trace gases

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Some important Trace gases

• Hydroxyl radical (OH)
• Reactive nitrogen species and the nitrogen cycle
• Hydrocarbons, Carbon monoxide
• Ozone
• Sulfur compounds and the sulfur cycle

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View prior to 1970s Inert troposphere(only
source of oxidants in the stratosphere)

• With an inert troposphere
• With increasing emissions from fossil fuel
  combustion will CO accumulate in the troposphere?
• View of an inert troposphere challenged
  Weinstock, 1969
• 14CO measurements in troposphere imply a 2-month
  lifetime for CO ? there MUST be a tropospheric
  sink!

OH
H2O,O3
CO2
CO
stratosphere
CO
troposphere
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• Primary source of tropospheric OH Levy, 1971
• O3 h? ? O2 O 290 nm lt?lt330 nm
  
• O M ? O M M (third body)
  O2 or N2
• O O2 M ? O3 M
• O H2O ? OH OH

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(99)
2 OH
(1)
Solar radiation (290lt?lt330 nm)
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Tropospheric OH production takes place in a
narrow UV window (300-320 nm)
30o equinox midday Solar spectrum
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Sinks of OH

• Dominant sinks of OH in the global troposphere
• CO OH? CO2 H
• CH4 OH ? CH3 H2O ?CO
• Over continents, reactions with non-methane
  hydrocarbons (NMHCs) dominates
• NMHC OH ? products
• Lifetime of OH 1 second!

NMHCs
CO
CH4
CO
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The OH titration problem
O2
Source of COCH4gtgt source of OH If no other
sources, OH would be titrated. ? CO and CH4
would accumulate to very high levels!!
h?
O3
stratosphere
H2O2
O3
OH
HO2
h?, H2O
CO
troposphere
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Global OH concentrations model calculations
January
July
Make you own plots http//www.atmos.washington.e
du/jaegle/geoso3_start.html
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Have human activities changed the oxidizing
capacity of the atmosphere?
O3
NO

• Since pre-industrial times CO has increased by
  factors of 3-4
• NO has increased by factors of 2-8
• . What has happened to OH?
• NO ? ? increase in OH
• CO ? ? decrease in OH

OH
HO2
h?, H2O
CO, hydrocarbons
troposphere
? Little change in OH globally (buffering)
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Reactive nitrogen species and the nitrogen cycle

• Molecular nitrogen N2 , 78 (99.99 of all
  nitrogen)
• Nitrous oxide N2O, 310 ppmv
• Reactive nitrogen species NOy (pptv-ppbv)
• NOy NONO2(NOx) NO3N2O5HNO3 PAN
  (CH3C(O)OONO2)
• Ammonia NH3 pptv-ppbv

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Sources of N2 and N2O
HNO3
CONTINENTS 9 109 Tg(N)
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Role of biological processes in the nitrogen cycle
atmosphere
soil
N2
Bacterial fixation
NH4
NO3-
N2
Nitrification
Denitrification
Plants and soil microorganisms
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Sources of nitrogen oxidesand ammonia
Fluxes in TgN/year
Aircraft
0.5
NOx 32 TgN anthropogenic 11 TgN
natural
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Chemistry of nitrogen oxides
O3
oxidation
NO2
NO
HNO3
h?
Wet/dry deposition
Loss (hours)
Tropospheric NO2 columns from the GOME satellite
August 2000
1015 cm-2
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Some important Trace gases

• Hydroxyl radical (OH)
• Reactive nitrogen species and the nitrogen cycle
• Hydrocarbons, Carbon monoxide
• Ozone
• Sulfur compounds and the sulfur cycle

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Methane, CH4
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The budget of CH4
Anthropogenic sources 70
CO?CO2
Fluxes in TgC/year
Historical methane trend
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Historical trend of methane
IPCC, 2001