1 Announcements • Extra credit videos due on Tuesday • Course summary and review for final next Thursday • Study guide will be posted this weekend • Final exam: Monday, March 15, 8 – 10 AM Atmospheric Pollution and Global change Are people responsible? What is our responsibility? Topics • Acid rain and smog • The ozone hole • Green-house gasses and global warming Photochemistry I • Ozone creation (ground level) • NO 2 + light → NO + O* • O* + O 2 → O 3 (Ozone generated) • NO + O 3 → NO 2 + O 2 → little O 3 generated • Nitric oxide + VOCs • NO + VOC → peroxyacetyl nitrates • (O 3 is not consumed) → net O 3 generated • Ground-level ozone is a health hazard NO NO NO Photochemistry II • Formation of hydroxyl radical (upper troposphere) •O 3 + UV light → O 2 + O* • O* + H 2 O → 2 OH (hydroxyl radical) • Important reactions with hydroxyl radical • OH + NO 2 + catalyst (SPM)→ 2HNO 3 (nitric acid produced) • 2OH + SO 2 + catalyst (SPM)→ H 2 SO 4 (sulfuric acid produced)
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1
Announcements
• Extra credit videos due on Tuesday• Course summary and review for final next
Thursday• Study guide will be posted this weekend• Final exam: Monday, March 15, 8 – 10 AM
Atmospheric Pollution and Global change
Are people responsible?What is our responsibility?
Topics
• Acid rain and smog• The ozone hole• Green-house gasses and global warming
Photochemistry I
• Ozone creation (ground level)• NO2 + light → NO + O*• O* + O2 → O3 (Ozone generated)• NO + O3 → NO2 + O2 → little O3 generated
• Nitric oxide + VOCs• NO + VOC → peroxyacetyl nitrates • (O3 is not consumed) → net O3 generated
• Ground-level ozone is a health hazard
NO
NO
NO
Photochemistry II
• Formation of hydroxyl radical (upper troposphere)
Fate of nitric and sulfuric acids pH tolerances of some aquatic organisms
Figure from www.epa.gov/airmarkets/acidrain/effects/
Effects of acid rain• Daibutsu – Great
Buddha of Kamakura, cast in 1252 A.D.
• Over 40 feet tall, 121 tons
• Serious corrosion from Korean and Chinese industries
pH and SO2
• New Hampshire stream data
• Inverse relationship
• pH still low!• Years of acid rain
reduced buffering capacity of streams
Hubbard Brook LTER program: lternet.edu
VOCs and NOx produce photochemical smog
Mexico City
Trends in average air pollutant concentrations in United States
Source: www.epa.gov/airtrends
Lead
Sulfur Dioxide
Year
00.0020.0040.0060.0080.01
0.0120.014
1980 1990 2000 2010
Con
cent
ratio
n (p
pm)
00.0050.01
0.0150.02
0.025
0.03
1980 1990 2000 2010
Con
cent
ratio
n (p
pm)
Year
Nitrogen Dioxide
0
2
4
6
8
10
1980 1990 2000 2010
Con
cent
ratio
n (p
pm)
Carbon Monoxide
00.20.40.60.8
11.21.41.6
1980 1990 2000 2010
Con
cent
ratio
n (µ
g m
-3)
3
Ozone hole:September 2006(largest on record)
http://ozonewatch.gsfc.nasa.gov
Global change policy that all support: Ozone depletion and CFCs Atmosphere’s layers
Temperature profile
The ozone problem
• O3 in the stratosphere absorbs UV radiation
• CFCs and other compounds destroys O3 in the stratosphere
• UV radiation has consequently increased at the earth’s surface
• Rates of skin cancer, cataracts, and other medical problems have increased
Why produce CFCs?Chlorofluorocarbon (CFC): chlorine, fluorine, and carbon compound
• CFCs stable, non-toxic in troposphere• Exchange heat – refrigerants and propellants• Broken down in stratosphere by UV light• Example: CFC-11 (CCl3F) Trichlorofluoromethane
Methane CFC-11
H F| |
H – C – H Cl – C – Cl| |H Cl
Photochemistry III: Chlorine cycle
O2 + UVB → 2 O*
O* + O2 → O3
O3 + UVB → O* + O2
O* + O3 → 2 O2
With CFCs:
CFCl3 + UVB → CFCl2 + Cl
Chlorine cycle:
Cl + O3 → ClO + O2
ClO + ClO → 2Cl + O2
Ozone created and destroyed absorbing UV
Photochemical reactions in the stratosphere:
Polar stratospheric clouds and chlorine nitrate provide catalyst for these reactions
Illustration of the chlorine cycle
http://www.umich.edu/~gs265/society/ozone.htm
4
Troposheric vs. Stratospheric O3
Tropospheric ozone Stratospheric ozone• Bad Good• Formation
• NO2 + light + VOCs - UV light• Problem
• Reactive molecule - Loss of O3 incauses health problems stratosphere leads
to increased UV
Ozone and UV radiation
• Relationship between ozone and UV index in New Zealand
• Source:Science (1999) 285: 1709-1711
Ozone, sunburn and skin cancer?
http://www.esrl.noaa.gov Jemal 2001. J. National Cancer Inst.
Melanoma amongUS whites
Decrease in stratospheric ozone since 1956 (spring)
Measurements of ozone on the ground (Dobson spec) and via satellite (TOMS)
Ozone and CFC policy• 1987: Montreal protocol adopted
by 140 nations- Scale back CFC production
50% by 2000.- Amendments – complete
phase out by 1996• Problem: long residence times• Why was it so easy to phase out
CFCs?
Chlorofluorocarbon production
Greenhouse gases and global warming
Causes, consequences, evidence
5
What is certain
• 35% increase in CO2 concentrations in last 150y• This change in atmospheric composition should
lead to global warming (climate models)• Temperature measurements over last century
document planetary warming• The primary cause of changing CO2 is fossil fuel
burning and (secondarily) burning of forests• Global sea levels are rising at ~ 3mm per year• Glaciers around the globe are melting rapidly
What is less certain
• Future changes in temperature, sea-level rise, and ice melt
• Extent of coastal flooding• Role of global warming in generating more intense
hurricanes• Regional changes in climate patterns• Effects on ecosystems• Effects on society (Inuit, Bangladesh, Tuvalu)
Changes in atmospheric CO2 concentration
>20% increase since 1958, >35% since 1850 (ice core data)
Fig. 17.18
Atmosphere is transparent to lightGasses - CO2, CH4, N2O, O3, CFC’s, H2O
absorb infared radiationemitted by the earth’s surface
What makes a “good” greenhouse gas?
• Heat-trapping capacity• E.g., N2O ≈ 300 CO2 and CH4 ≈ 21 CO2
• Concentration in atmosphere• E.g., CO2: 365 parts per million
N2O: 315 parts per billion• Residence time in atmosphere
• E.g., CO2: >100 yCH4: 5-10 y
Global carbon cycle and budget
6
Evidence that increased atmospheric CO2 is primarily due to fossil fuel combustion
• Carbon budget• Parallel decline of the 14C/12C ratio of atmospheric
CO2 due to absence of 14C in fossil fuels• Parallel decline of the 13C/12C ratio of atmospheric
CO2 due to the fact that fossil fuels and plants are depleted in 13C
• Parallel decline in the O2 concentration of the atmosphere, which indicates the increase in CO2 is due to combustion
Consequences of increased greenhouse gas concentrations
Plots from the IPCC Working Group 1 report (2007)
1928 2000
South Cascade Glacier, Glacier Peak Wilderness, WA Columbia Glacier, SE Alaska1980
Columbia Glacier 2005Nine-mile retreat
Formerly snow-capped Mount Kilimanjaro stripped of its snowcap for the first time in
11,000 years
Role of climate models
7
Ancient CO2 levels from bubbles trapped in ice cores, temperature
from ice oxygen isotope ratios
Historical context from temperature and CO2 recorded in ice cores…
IPCC 2007Sea level rise: 20 to 60 cm by 2100Hurricane Katrina
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Recent increase in category 4 and 5 hurricanes
1975–1989 1990–2004
East Pacific Ocean 36 49 West Pacific Ocean 85 116 North Atlantic 16 25 S.W. Pacific 10 22 North Indian 1 7 South Indian 23 50
Number Cat 4 and 5 hurricanesChanges in hurricane intensityWebster et al. (2005) Science
1 meter increase displaces 17 million people
Regional climate change Declining snowpack
Increased seawater temperature in Pacific Northwest
2 °F increase in sea surface temperature near Victoria, B.C. (PSAT 2005)
What can you do to reduce global warming?
• Buy and support green energy – You’re already doing this!!!
• Purchase a fuel-efficient car (rated up to 32 mpg or more) to replace your most frequently used automobile.• CO2 reduction = 5,600 lbs/year• Or, use alternative modes of transportation
• What can the United States do?
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Kyoto protocol
• Agreed to unanimously in 1997• Mandatory greenhouse gas emissions targets
• Reduce GHG emissions to ~5% below 1990 levels between 2008 and 2012
• U.S: reduce GHGs to 7% below 1990 levels• Decrease emissions or increase GHG “sinks”• Emissions trading• Copenhagen Climate Conference