Air Quality 101
Rice Air CurriculumTeacher Training
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Leading Atmospheric Constituents
• Nitrogen (N2) 78%
• Oxygen (O2) 21%
• Argon (Ar) 1%
• Water Vapor (H2O) 0-3%
• Carbon dioxide (CO2) 0.039%
Most air pollutants are in very small quantities (parts per million or billion) but affect our health
and climate.
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Categories of Atmospheric Compounds• Air pollutants: Substances that directly harm
health of humans, wildlife, or vegetation– Air toxics: Carcinogens, mutagens, neurotoxins– Respiratory irritants– Substances that cause cardio-vascular impacts– Substances that damage crops, forests, ecosystems
• Particulate matter: Solid or liquid microscopic particles suspended in air
• Ozone depleters: Substances that destroy stratospheric ozone
• Climate-influencing compounds: Greenhouse gases and particles that impact radiative budget
Particulate Matter
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Particulate Matter• Aerosol: Liquid or solid particles suspended in air• Wide range of chemical composition• Sizes range from <1nm to >10 μm
– Large particles settle out quickly– Fine particles (<2.5 μm (PM2.5)) most damaging to visibility
& health (respiratory, cardio-vascular, mortality)
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Impacts of PM• Health effects
– Fine particles go deep in lungs, to bloodstream– Respiratory and cardiovascular disease– Mortality
• Visibility/Haze• Climate• Regulatory concern
– Houston barely attains current standard– EPA tightened 24-hr but not annual standard
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Ozone (O3)
Stratospheric & Tropospheric Ozone:“Good up high, Bad nearby”
• In stratosphere, ozone forms naturally when Sun’s intense UV rays split oxygen:– O2 + hv O + O
– O + O2 O3
– This “good ozone” blocks UV rays– Stratospheric ozone can be destroyed by CFCs
• In troposphere, intense UV rays already blocked. Ozone instead forms as a pollutant:– Nitrogen oxides + Hydrocarbons + Sunlight O3
– “Bad ozone”: air pollutant and greenhouse gas
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Stratospheric Ozone Hole
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Montreal Protocol drastically curtailed ozone depleting emissions
WMO/UNEP Scientific Assessment of Ozone Depletion, 2010
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Impacts of Montreal Protocol:Halocarbon Concentrations
NOAA
45 yrlifetime
100 yrlifetime
5 yrlifetime
35 yrlifetime
Ozone projected to recover as halocarbon levels decline
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NO
NO2
HO2
OH
RO2
VOC
O3
Ground-level Ozone “Smog”
VOC NOx O3
HydrocarbonsNitrogenOxides
Sunlight & Heat
Tropospheric NOx Cycle
N2O NO NO2
O3
hνHNO3
O(1D) O ClONO2
BrONO2
ClO, BrO
Red: Ox destructionGreen: Ox productionBlack: No change in Ox
Blue: Reservoir Species*: Dominant pathway during daytime
hv
OH
NO3
O3
hν
N2O5
HO2 and CH3O2, other RO2
CO, CH4, VOCs
Oxidation by
OH, etc.
Directemissions
hν
*
*
deposition
Sources of Ozone-forming Emissions
• Nitrogen Oxides– Vehicles– Power plants– Other industry and equipment
• Hydrocarbons– Natural vegetation– Vehicles– Refineries / Chemical plants– Other sources
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Ozone Impacts
• Health effects– Asthma and other respiratory illnesses– Recently linked to mortality
• Regulatory concern– Houston, Dallas, many other cities fail to
attain limits
• Atmospheric oxidant– Oxidizes certain VOCs– Contributes to formation of OH oxidant
• Greenhouse gas
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Emissions Trends
Strong declines in ozone, but many cities still exceed 75 ppb
18http://www.tceq.state.tx.us/assets/public/implementation/air/sip/hgb/hgb_sip_2009/09017SIP_Ch5_ado.pdf
Houston US Cities
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Ozone Non-attainment: 75 ppb standard
Map from US EPA
Climate Change Overview
• Is Earth warming?
• Natural or anthropogenic causes?– Overview Earth’s radiative balance &
greenhouse effect
• Impacts
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Evidence of recent climate change
IPCC, 2007
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National Geographic
Global US
Additional evidence of warming
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IPCC, Physical Basis Technical Summary, 2007
Past decade was warmest recorded
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Hansen et al 2010
This summer’s weather
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http://www.columbia.edu/~mhs119/Temperature/
Anomaly (°C) relative to 1951-1980 mean
In the news: Arctic sea ice reaches all time minimum extent, August 26, 2012
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NASA: http://climate.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=767
Yellow line shows average minimum, 1979-2010
Climate Fundamentals: Earth’s Radiative Balance and Greenhouse Effect
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(Trenberth et al., BAMS, March 2009)
Yellow: Solar UV
and Visible Radiation
Beige: Infrared
Radiation
Radiation proportional to TK
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Greenhouse gases absorb and re-radiate infrared at atmosphere’s cooler temperature
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Earth’s Carbon Cycle
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Rising Greenhouse Gas Levels
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IPCC, 2007
CO2
CH4
N2O
Total Radiative Forcing
Causes of Radiative Forcing, 1750-2005
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IPCC, 2007
Greenhouse gas radiative forcing (W/m2) well understood
Key Scientific Uncertainty: How much warming per radiative forcing (°C/W-m2)
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IPCC, 2007
Both anthropogenic and natural forcings are needed to model temperature record
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IPCC, 2007
Projected Impacts of Further Warming
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IPCC, Impacts SPM, 2007
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