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
Transcript of Atmospheric Chemistry 2013 - Department of Atmospheric...
Atmospheric Chemistry
• October 29 – Introduction • October 30 – Joel Thornton Pollution • October 31 – Becky Alexander Biogechemical
Cycles • November 1 Quiz
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
1948 – noontime (Donora, PA)
Urban smog around the world today
New Delhi
Mexico City
Los Angeles
Seoul
Beijing
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)
Acid rain
Acidified Forest, Oberwiesenthal, Germany (1991)
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
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
Stratospheric ozone depletion
Tropospheric ozone column: Jun-Aug à Downward trends in ozone column on a global scale
Chlorine chemistry!
Recovery!
Large increases in greenhouse gases and aerosols since pre-industrial times
up by 30%
up by 150%
up by 10%
Climate change
Residence Time
Residence time = Mass/Removal rate
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?
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
TRANSPORT of gases Source: Introduction to Atmospheric Chemistry, Jacob, D. J., 1999
Residence times and spatial variability
Figure 5.1
Sources of gases
• Biological: Land/Ocean • Solid earth • Mechanical generation (sea salt and dust) • Anthropogenic: Fossil fuel, biomass
burning, industrial • Photochemical
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…)
Biological sources - Oceans • Oceans: DMS, H2S, COS, CH3Cl, CH3I, hydrocarbons
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
Dust and sea salt = generation by the action of wind
Fossil fuel emissions (concentrated in the northern hemisphere)
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
Fire animation March 2000 to August 2011
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD14A1_M_FIRE
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!
Some important Trace gases
• Hydroxyl radical (OH) • Reactive nitrogen species and the
nitrogen cycle • Hydrocarbons, Carbon monoxide • Ozone
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
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%
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
