The Atmosphere: Oxidizing Medium In Global Biogeochemical Cycles

EARTHSURFACE

Emission

Reduced gasOxidized gas/aerosol

Oxidation

Uptake

Reduction

Only A Narrow UV Window (300-320 nm) for O(1D) Production

30o equinoxmiddaySolar spectrum

3Oj Id

O(1D) production in the troposphere?

OH Radical: Main Tropospheric Oxidant

O3 + hv O2 + O(1D) (1)

O(1D) + M O + M (2)

O(1D) + H2O 2OH (3)

Primary source:

Sink: oxidation of reduced species

CO + OH CO2 + H

CH4 + OH CH3 + H2O

HCFC + OH H2O + …

Major OH sinks globally

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 of OH in the troposphere?

Wetlands Termites Other Natural Natural Gas Livestock Rice Paddies Other Anthropogenic

Global Sources of Methane

Natural Sources

Anthropogenic Sources

Global Distribution of Methane

NOAA/CMDL surface air measurements

Historical Trends In Methane

Historical methane trend

Recent methane trend

RECENT TREND IN METHANE

Fossil Fuel Combustion Biomass Burning Vegetation Ocean Oxidation of Methane Oxidation of other hydrocarbons

Global Sources of CO

Satellite Measurements of Lower Tropospheric CO

Satellite Measurements of Upper Tropospheric CO

Global Distribution of CO

NOAA/CMDL surface air measurements

O3

O3 + hv OH + OH H2O

Stratosphere

CO CH4

1-2 x1013

moles yr-1 2-4 x1013

moles yr-1

6-10 x1013

moles yr-13 x1013 moles yr-1

OH only from strat O3 would be titrated

X X

Troposphere

How are tropospheric OH levels maintained?

Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS-CHEM model results for 1997 (contours).

GEOS-CHEM tropospheric ozone columns for July 1997.

GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONEGLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE

Li et al. [2001]

NONOxx EMISSIONS (Tg N yr EMISSIONS (Tg N yr-1-1) TO TROPOSPHERE) TO TROPOSPHERE

FOSSIL FUEL 23.1

AIRCRAFT 0.5

BIOFUEL 2.2

BIOMASSBURNING 5.2

SOILS 5.1

LIGHTNING 5.8

STRATOSPHERE 0.2

MAPPING OF TROPOSPHERIC NOMAPPING OF TROPOSPHERIC NO22

FROM THE GOME SATELLITE INSTRUMENT (July 1996)FROM THE GOME SATELLITE INSTRUMENT (July 1996)

Martin et al. [2002]

LIGHTNING FLASHES SEEN FROM SPACE (2000)LIGHTNING FLASHES SEEN FROM SPACE (2000)

DJF

JJA

PEROXYACETYLNITRATE (PAN) AS RESERVOIR PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NOFOR LONG-RANGE TRANSPORT OF NOxx

NONOxx, HNO, HNO33, AND PAN OVER THE TROPICAL PACIFIC, AND PAN OVER THE TROPICAL PACIFIC

Aircraft observations from PEM-Tropics B, March-April 1999Aircraft observations from PEM-Tropics B, March-April 1999

Staudt et al. [2003]

QUESTIONSQUESTIONS

1.    The prospect of hydrogen-fueled cars is leading to study of the effect of increasing atmospheric H2. Would you expect H2 to be oxidized by OH? What would be the effect on the oxidizing power of the atmosphere? 2.    Loss of NOx in the troposphere takes place by NO2+OH, same as in the stratosphere. What is the effect of this reaction on tropospheric ozone?

QUESTIONQUESTION

 

1. How does the lifetime of NOx respond to a change in the NOx concentration? If NOx emissions were to double, would NOx concentrations more than double or less than double?