Transcript Week 7 Slides

This Week—Tropospheric Chemistry
READING: Chapter 11 of text
Tropospheric Chemistry Data Set Analysis
The Atmosphere: Oxidizing Medium
Reduced gas
EARTH
SURFACE
Oxidation
Oxidized gas/
aerosol
Uptake
Emission
Reduction
O(1D) Production in Troposphere?
Actinic Flux vs wavelength
(O1D production requires < 320nm)
30o equinox
midday
Solar spectrum
O(1D) production in the Troposphere?
jO 3           I    d 

OH Radical: Main Tropospheric Oxidant
Primary source:
O3 + hv  O2 + O(1D)
(1)
O(1D) + M  O + M
(2)
O(1D) + H2O  2OH
(3)
Sink: oxidation of reduced species
CO + OH  CO2 + H
CH4 + OH  CH3 + H2O
Major OH
sinks globally
HCFC + OH  H2O + …
GLOBAL MEAN [OH] = 1.0x106 molecules cm-3
Questions
1. How would a thinning of the stratospheric ozone
layer affect the source of OH in the troposphere?
2. How might global warming affect the source rate of
OH in the troposphere?
Global Sources of Methane
Anthropogenic Sources
Natural Sources
Wetlands
Termites
Other Natural
Natural Gas
Livestock
Rice Paddies
Other Anthropogenic
Global Distribution of Methane
NOAA/CMDL surface air measurements
Historical Trends In Methane
Recent methane trend
Historical methane trend
Global Sources of CO
Fossil Fuel Combustion
Biomass Burning
Vegetation
Ocean
Oxidation of Methane
Oxidation of other hydrocarbons
Satellite Measurements
Lower Tropospheric CO
Satellite Measurements
Upper Tropospheric CO
Global Distribution of CO
NOAA/CMDL surface air measurements
OH Titration Problem
Stratosphere
O3
1-2 x1013
moles yr-1
H O
2-4 x1013
moles yr-1
Troposphere
2
O3 + hv 
2OH
CO
3 x1013
moles yr-1
X X
6-10 x1013
moles yr-1
CH4
OH only from strat
O3 would be titrated
HOx and NOx Catalyzed O3 Production
O3 + h
H2O
CH4
CH3O
OH
CO
O
NO
HO2
H2CO + h
O2
2
NO
2
CH3O
H2CO O2
O
NO
CH3O2
O
h
HO2
NO
2
2
O3
Questions
1. NO also reacts with O3 (as in the stratosphere)
to produce NO2. In fact, the rate of conversion
of NO to NO2 is dominated by this reaction in
the troposphere. What is the effect of this
reaction on O3 production and HOx cycling?
2. Loss of NOx in the troposphere takes place by
NO2+OHHNO3, same as in the stratosphere.
What is the effect of this reaction on
tropospheric ozone?
3. What’s the maximum number of O3 that can be
produced from the oxidation of 1 CH4?
Tropospheric NOx Sources (Tg N yr-1)
Probably bigger
according to
recent UW
ATMSCI research
LIGHTNING
5.8
STRATOSPHERE
0.2
SOILS
5.1
BIOMASS
BURNING
BIOFUEL
5.2
AIRCRAFT
2.2
0.5
FOSSIL FUEL
23.1
Tropospheric NO2 from Space
NOx Lifetime < 1 day! Fraction transported away from source
regions very low
Martin et al. [2002]
Lightning Flashes From Space
DJF
JJA
Long-Range Transport of NOx
By NOx Reservoir: Peroxyacetyl Nitrate (PAN)
NOx Sources in Remote Regions
O3
NO
HO2
RO2
CO2
h
NO2
HO
RO
CO
RH
HO2NO2
RO2NO2
Questions
1. How would you calculate the chemical lifetime of NOx?
2. Sketch a typical vertical profile for NOx.
3. Anthropogenic activity has lead to the increase of NOx,
CO, and CH4 emissions, with roughly factors of 2-4
increases of each over pre-industrial times. How have
these changes affected OH concentrations?
Predicted Change Since Pre-Industrial Times
CO and CH4 tend
to decrease OH
NOx and O3 tend
to increase OH
[OH]global ~
constant
Global Distribution of Ozone
January
What are the main
controls on
tropospheric O3?
August
Global Tropospheric O3 Budget
O3
Stratosphere
400-1100 Tg yr-1
Troposphere
Flux from
Stratosphere
O3
3400-5700 Tg yr-1
Chemical Production
During NOx/HOx catalyzed photo-oxidation of CO, CH4
Chemical Loss
500-1500 Tg yr-1
Deposition
HOx catalyzed destruction
O(1D) + H2O
o o