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Global WarmingOzone DepletionAcid RainIndoor Air Pollution
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Is the climate becoming warmer?
The Earth's surface temperature has risen by about 1 oF in the past century, with accelerated warming during the past two decades. New and stronger evidence shows that most of the warming over the last 50 years is attributable to human activities. Human activities have altered the chemical composition of the atmosphere through the buildup of greenhouse gases. The heat-trapping property of these gases is undisputed, although uncertainties exist about exactly how earth's climate responds to them.
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Global temperature trend
Note that these are surface temperatures and mostly overland.
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What cause the temperature of the atmosphere to go up?
Possible mechanisms: Natural variation Solar activity Greenhouse effect – increasing “greenhouse”
gases (GHGs) such as CO2, CH4, N2O (nitrous oxide), CFC, hydroflurocarbon (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and black carbon (actually H2O is very efficient, too, but at present it is assumed to be in steady state).
CO2 64% CH4
19%
N2O 6%CFCs 10%
Others 1%
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The real greenhouse
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The (Atmospheric) Greenhouse Effect
GHGs can absorb terrestrial radiation (peaking at infrared wavelength) and re-radiate in all directions. Part of the re-radiation is sent back to the surface.
Earth’s Energy Balance
Of total incoming light from the sun: 50% (mainly visible, 400-750 nm) reaches
surface and is absorbed; 20% absorbed by atmospheric gases (UV by
ozone; IR by CO2 and H2O; 30% reflected back (by clouds, snow etc).
As a warm body the earth emits IR thermal energy; some redirected back to earth - average temp +15 oC. If not for this natural greenhouse effect the surface would be covered by ice (-18 oC).
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Atmospheric Carbon Dioxide
The chart shows a steady increase of CO2 concentration in the last five decades.
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Is everybody convinced of the GHG - global warming theory?
At this point, it appears that the warming itself is real – the surface temperature indeed becomes higher in the last few decades.
The question is – Is the warming caused by the greenhouse gases (especially CO2)?
Some groups, especially the Intergovernmental Panel on Climate Change (IPCC) members argue strongly for it. But there are other groups that are not convinced.
World leaders gathered in Kyoto, Japan, in December 1997 to consider a world treaty restricting emissions of GHGs.
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The Kyoto Agreement
Legally binding Protocol: industrialized countries to reduce their collective greenhouse gas emissions by 5.2% by 2012.Cuts to most important gases: CO2, methane (CH4), and nitrous oxide (N2O) - measured against 1990 baseline. Cuts in long-lived industrial gases: hydrofluoro-carbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6) - measured against 1990 or 1995 baseline.
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Absorption by GH Gases
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Greenhouse Gases
GHGs absorb long wavelength radiation and scatter it, warming the atmosphereIndividual gases absorb different wavelengthsGlobal Warming Potential (GWP) is a measure of the radiative effects of gases in the atmosphereGWP depends on the concentration of a gas, its residence time, and the time period of the calculationGWP is used to compare the GH effects of different gases; CO2 is standard of GWP = 1
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Some Greenhouse Gases
Gas Conc.1750
Conc. 1998
Lifetime (yrs)
GWP
CO2 278 ppmv 365 ppmv 50-200 1
CH4 700 ppbv 1745 ppbv 10 23
N2O 270 ppbv 314 ppbv 120 296
CFC-11
0 268 pptv 50 4600
CFC-12
0 533 pptv 102 5200
CFC-13
0 4 pptv 400 14,000
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More intense storms…
Hurricanes get their energy and staying power from warm water in the tropical oceans. As waters get warmer, we expect that hurricanes will become more intense.Significant change not yet observed.Hurricane Andrew (above) was the most costly natural disaster in US history! Will we see more like this one?Katrina
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Major impact on Developed coastal regionsLow-lying island nationsIntensity of coastal flooding during storm surgesCoastal ecosystems
Higher sea level…
As water warms, it expands.Glaciers are meltingObservation: 3mm/yr in past few decadesPrediction: ~0.5m rise by the end of this century, 2-4m in 500 years
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Options to Reduce GHG Emissions
Energy efficiency (any stage of the fuel cycle)Fuel switching: e.g. from coal to natural gas, use of H2
Renewables: hydro, wind, solar, biomassNuclear powerCO2 capture and storage
Forestry: improve management, long term solution
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GHG by Sector
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What is Acid Rain (Acid Deposition)?
Wet deposition refers to acidic rain, fog, and snow As this acidic water flows over and through the
ground, it affects a variety of plants and animals Dry deposition refers to acidic gases and particles ~1/2 of acidity in the ATM falls back to earth
through dry deposition The wind blows these acidic particles and gases
onto buildings, cars, homes, and trees Dry deposited gases/particles can also be washed
from trees and other surfaces by rainstorms, the runoff adds those acids to the acid rain, making the combination more acidic than the falling rain alone
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Acid Rain
Prevailing winds blow the compounds across state and national borders.Sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain
Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions.
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Acid Rain Formation
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“Good” Ozone vs. “Bad” Ozone
Stratospheric or “good” ozone is located 10-30 miles above the earth’s surfaceProtects the planet from harmful UV radiation
Also referred to as tropospheric ozone, urban ozone, and smogMay cause permanent lung damage and harms plants and ecosystemsCaused by nitrous oxide(NOx) and volatile organic compounds(VOC).
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Formation of “Bad” Ozone
The formation of ozone is complex and involves hundreds of chemical reactions.Simplified reaction:2NO + O2 2NO2
NO2 + hv NO + O
O + O2 + M O3 + Mhv represents short wavelength of light M represents a catalyst In this case, reactive hydrocarbons
(VOC). M is a product of the reaction so VOC
stay in the air to produce more harmful ozone.
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Depletion of “Good” Ozone
Destruction of stratospheric ozone is mainly caused by elemental chlorine atoms. It’s catalytic.Cl + O3 ClO + O2
ClO + O3 Cl + O2Only naturally-occurring chemical responsible for ozone depletion: methyl chloride, CH3Cl
Man-made chemicals: CCl4, CFCs (CFC12 – CF2Cl2, & CFC11 – CFCl3). These chemicals have no H, and can’t be attacked by atmospheric OH radical. Attack on CH3CCl3 is slow.
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Indoor Air Quality
Concentrations of some pollutants higher indoors (VOCs, PM)We spend more time indoorsWorkplace air regulated No objectives/standards/regulatory body for residential indoor air
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Air Pollution in the OfficeAsbestos ceiling tiles, floor tiles, heating
system insulationCarbon monoxide garages, motor vehicles
Formaldehyde glues, partitions, carpeting,
panelingMicro-organisms humidifiers, washrooms, air
conditioners, dehumidifiers, ventilation pipes and ducts
Tobacco smokeVolatile organic compounds cleaning
compounds, paints, solvents, copy machines markers and pens
Ozone copy machines
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Air Pollution At HomeBedroom window air conditioners, room
humidifiers and dehumidifiers, kerosene or gas heater
Living room fireplace, carpet and drapes,
paneling, Environmental tobacco smoke (ETS)
Kitchen gas appliances, biological
contaminants, cleaning agents
Garage auto engine,
lawn mower, paints and hobby materials, pesticides
Furnace room forced air
furnace, humidifiers, dehumidifiers, gas appliances
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Simple Box Model of Residential Indoor Air - Steady state
airin ion concentrat pollutant = c
out) and(in rate flowair = Q
sink pollutant = R
rate)emission (mass source pollutant = S
air enteringin ion concentrat pollutant = c
i
o
Q
RScc oi
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Air Circulation and Exchange
Circulation of 6-9 air exchanges per hour (some outside air, some recirculation)Dining room occupancy, 70 people/1000 ft2
Fresh outside air requirements:Smoking: 35 cfm/personNon-smoking: 7 cfm/person
Infiltration rate for typical home: 0.5 - 2 air exchanges per hour (closed doors and windows)
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Strategies For Reducing Pollutants In Indoor Air
Source controlVentilationAir cleaners
Decreasing effectiveness
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http://www.arb.ca.gov/cc/non-co2-http://www.arb.ca.gov/cc/non-co2-clearinghouse/non-co2-clearinghouse.htmclearinghouse/non-co2-clearinghouse.htm
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