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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)

• O3 + UV light → O2 + O* • O* + H2O → 2 OH (hydroxyl radical)

• Important reactions with hydroxyl radical• OH + NO2 + catalyst (SPM)→ 2HNO3

(nitric acid produced)• 2OH + SO2 + catalyst (SPM)→ H2SO4

(sulfuric acid produced)

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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)

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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

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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

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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

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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

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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…

…and Tree growth rings

“Hockey-stick” curve

Areas of less certainty

• Future projections• Extreme weather events• Regional climate change• Extent of future coastal flooding

Future projections

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