atmospheric chemistry 2013 - department of atmospheric...
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Atmospheric Chemistry
• October 29 – Introduction • October 30 – Joel Thornton Pollution • October 31 – Becky Alexander Biogechemical
Cycles • November 1 Quiz
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Atmospheric chemistry - what are the issues?
Climate Change (…1990s…)
Regional Air Pollution (…1950s…)
Acid rain (1960s…)
Stratospheric Ozone depletion
(1970s…)
Atmospheric CHEMISTRY
à Factors controlling the natural composition of the atmosphere à Effects of human activities in changing atmospheric composition
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1948 – noontime (Donora, PA)
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Urban smog around the world today
New Delhi
Mexico City
Los Angeles
Seoul
Beijing
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Urban/Regional air pollution
Tropospheric ozone column: Jun-Aug
160 million people
http://www.epa.gov/oar/oaqps/greenbk Counties exceeding U.S. EPA’s National Air Quality Standards (NAAQS)
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Acid rain
Acidified Forest, Oberwiesenthal, Germany (1991)
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Acid rain
Tropospheric ozone column: Jun-Aug
1989-1991 2005-2007
Wet sulfate (SO42-) deposition Getting better in the U.S. …
… but worsening in Asia
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Stratospheric ozone depletion
Tropospheric ozone column: Jun-Aug à Downward trends in stratospheric
ozone column on a global scale [WMO, 2010]
October monthly averages
1970s: normal polar ozone
Ozone hole
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Stratospheric ozone depletion
Tropospheric ozone column: Jun-Aug à Downward trends in ozone column on a global scale
Chlorine chemistry!
Recovery!
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Large increases in greenhouse gases and aerosols since pre-industrial times
up by 30%
up by 150%
up by 10%
Climate change
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Residence Time
Residence time = Mass/Removal rate
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The global carbon cycle for the 1990s IPCC (2007), Fig 7.3
What is the residence time of an atmospheric CO2 molecule with respect to removal by plants and the ocean?
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Inflow Fin! Outflow Fout!X!E!
Emission! Deposition!
D!
Chemical!production!
P! L!
Chemical!loss!
Atmospheric “box”;!spatial distribution of X within box is not resolved!
sources inF E P= + +∑ sinks outF L D= + +∑
sources - sinksdmdt
=∑ ∑mass balance equation:
Lifetime (aka residence time): x xx
m mtotallossrateSinks
τ = =∑
One Box Model
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TRANSPORT of gases Source: Introduction to Atmospheric Chemistry, Jacob, D. J., 1999
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Residence times and spatial variability
Figure 5.1
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Sources of gases
• Biological: Land/Ocean • Solid earth • Mechanical generation (sea salt and dust) • Anthropogenic: Fossil fuel, biomass
burning, industrial • Photochemical
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Biological sources - Land • Photosynthesis: CO2 + H2O + h à CH2O + O2 • Biological source of CH4: swamps, rice paddies, termites, ruminants • Biological sources of N2O and NO: nitrifying and denitrifying bacteria in soils • Plants: Reactive hydrocarbons (isoprene, terpenes, etc…)
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Biological sources - Oceans • Oceans: DMS, H2S, COS, CH3Cl, CH3I, hydrocarbons
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Solid earth • Volcanoes: SO2, H2S, COS, particles, H2O, CO2, HCl… • Rocks (radiogenic): He (decay of uranium and thorium), Argon (decay potassium-40), radon (decay of uranium-238 )
• Weathering of CaCO3 rocks
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Dust and sea salt = generation by the action of wind
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Fossil fuel emissions (concentrated in the northern hemisphere)
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Biomass burning
Biomass burning emissions (concentrated in the tropics) Agricultural and natural (lightning)
Duncan et al., 2003
http://earthobservatory.nasa.gov/IOTD/view.php?id=9060
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Fire animation March 2000 to August 2011
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD14A1_M_FIRE
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Photochemical sources/sinks • Gases produced photochemically in the atmosphere: O3, OH, HO2, HCHO, H2O2, CH3OOH, NO2, NO3, HNO3, CO, SO2, etc… • Sinks: atmospheric oxidation followed by dry or wet deposition
EARTH!SURFACE/!
OCEAN!
Emission!
Reduced gas! Oxidized gas/!aerosol!
Oxidation!
Dry deposition/!Wet deposition!
Reduction!
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Some important Trace gases
• Hydroxyl radical (OH) • Reactive nitrogen species and the
nitrogen cycle • Hydrocarbons, Carbon monoxide • Ozone
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View prior to 1970s: Inert troposphere (only source of oxidants in the stratosphere)
troposphere
stratosphere
CO
H2O, O3 OH
CO
CO2
With an inert troposphere: è 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 à there MUST be a tropospheric sink!
slow
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Primary source of tropospheric OH [Levy, 1971] O3 + h à O2 + O* 290 nm <<330 nm O* + M à O + M M (“third body”) = O2 or N2 O+ O2 + M à O3 + M O* + H2O à OH + OH
2 OH Solar radiation (290<<330 nm)
(~1%)
(~99%)
~1%
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Sinks of OH Dominant sinks of OH in the global troposphere: CO + OHà CO2 + H CH4 + OH à CH3 + H2O à…CO Over continents, reactions with non-methane hydrocarbons (NMHCs) dominates: NMHC + OH à products Lifetime of OH ~ 1 second!
CO
hydrocarbons