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Tropospheric Air Quality Smog, Particulate Matter, Acid Deposition Tropospheric Air Quality 1 / 27
Tropospheric Air QualitySmog, Particulate Matter, Acid Deposition
Tropospheric Air Quality 1 / 27
Outline of Topics
1 OverviewIntroductionAir Quality StandardsCriteria Pollutant TrendsGeneration of Primary and Secondary Pollution
2 Photochemical SmogKiller SmogPhotochemical (LA) SmogSmog Formation
3 Particulate MatterSize and CompositionFormation of PMEffect of Pollution on PM
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US Air Quality
Has the Clean Air Act improved air quality?
Tropospheric Air Quality 3 / 27 Overview
What kind of health problems are caused by air pollution?
0 10 20 30 40
Coronary heart disease
Stroke
COPD
Acute lower respiratory infection
Lung cancer
Percentage of deaths
Outdoor
Indoor
WHO 2012: air pollution caused 7 million premature deathsOutdoor 3.7 million, indoor 4.3 million (some overlap)Acute lower respiratory infection: children under 5MIT study: 90,000–362,000 premature deaths in US in 2005
Tropospheric Air Quality 4 / 27 Overview
Lecture Question
What are the US National Ambient Air Quality Standards (NAAQS)?How do they work?
Pollutant Averaging Time US NAAQS WHO
O3 8-hr 75 ppb 47 ppbNO2 1-hr 100 ppb 93 ppbNO2 annual 53 ppb 20 ppb
PM-2.5 annual 12 µg/m3 10 µg/m3
PM-2.5 24-hr 35 µg/m3 25 µg/m3
PM-10 annual n/a 20 µg/m3
PM-10 24-hr 150 µg/m3 50 µg/m3
SO2 1-hr 75 ppb n/aSO2 24-hr n/a 7 ppbSO2 10-min n/a 175 ppb
CO 8-hr 9 ppm n/aCO 1-hr 35 ppm n/aPb 3-month 0.15 µg/m3 n/a
WHO stdsconverted fromµg/m3 whennecessary
EPA consideringnew O3 std65–70 ppb
EPA has primaryand secondary stds(primary shownhere)
What EPAconsiders a violationcan be complicated
Tropospheric Air Quality 5 / 27 Overview
Lecture Question
Based on NAAQS violations, which air pollutants are the biggest healthrisk in the US?
US populationwas 316M in2013
24% living in acountyexceedingNAAQS
Tropospheric Air Quality 6 / 27 Overview
Compare trends in ground-level ozone to the NAAQS.
1980 1985 1990 1995 2000 2005 2010
60
80
100
120
140
Year
Ozo
ne
con
cen
trat
ion
,p
pb
Annual 4th Max of Daily 8-hr avg Current daily NAAQS:75 ppb 8-hr max avg
3 exceedances allowed
Markers and trendlines:avg of the 4th highestmax
blue for national avg of222 stations, trendunder NAAQS in 2010
red for 3 Richmondstations, trend underNAAQS in 2013
Dashed blue lines are10th and 90thpercentiles
Tropospheric Air Quality 7 / 27 Overview
What is the trend in ‘typical’ (average) summer-time ozoneconcentration?
2000 2002 2004 2006 2008 2010 201240
45
50
55
60
Year
May
-Sep
tO
zon
eav
g,p
pb
urban
rural
Avg values, rather than4th-highest
Data adjusted to‘typical’ weatherconditions
NAAQS is 75 ppb
WHO guideline: 47 ppb
Urban: −0.80 ppb/yr
Rural: −0.71 ppb/yr
Tropospheric Air Quality 8 / 27 Overview
Compare trends in PM2.5 to the NAAQS.
2000 2004 2008 20120
5
10
15
20
Year
PM
2.5
,µg
/m3
Seasonally Weighted Annual Average Current NAAQS:12 µg/m3 (annual avg)
WHO guideline:10 µg/m3
Markers and trendlines:rolling 3-yr annual avgs
Blue for national avg of537 stations, trendunder NAAQS in 2005
Red for 4 Richmondstations, trend underNAAQS in 2006
Dashed blue lines are10th and 90thpercentiles
Tropospheric Air Quality 9 / 27 Overview
Primary and Secondary Pollution
What is the difference between primary and secondary pollution? Giveexamples.
Problem Primary Pollutant Secondary Pollutant
Photochemical smog NOx, VOCs O3, partially oxidized organics,NO2, HNO3, nitrate PM, or-ganic PM
Acid Deposition NOx, SO2 HNO3, H2SO4, acidic PM
Fine PM (PM2.5) NOx, SO2, VOCs nitrate PM, sulfate PM, organicPM
Primary (or precursor) pollutants are discharged into the air
They react to form secondary pollutants
A common theme in table above: photochemical oxidation of primarypollutants to form secondary pollutants
PM also formed by reaction of NH3 with acids to form (acidic) salts
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Lecture Questions
How are NOx and SO2 pollutants generated?
SO2 formed by burning anything that has sulfur in it
S + O2 SO2
Coal-fired power plants a common source
NOx formed by ANY combustion process hot enough to break the triplebond in atmospheric N2
Mostly formed as NON2 + O2 2 NO
NO and NO2 are rapidly interconverted (draw this)
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What activities generate the criteria pollutants and/or its precursors?
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What activities generate the criteria pollutants and/or its precursors?
Agriculture
Crops and livestock dustFertlizer applicationLivestock waste
Dust: fugitive emissions
Construction dustPaved road dustUnpaved road dust
Fuel combustion, mostly for heat and
electricity
Biomass, coal, natural gas, oil and otherorganic materials
Industrial processes
Cement manufacturingChemical manufacturingFerrous and non-ferrous metal millsMining; oil and gas extractionPetroleum refineriesPulp and paper millsStorage and transfer of materials
Mobile emission sources
AircraftCommercial maring vesselsLocomotivesNon-road equipment (diesel andgasoline)
Solvent use
Consumer and commercial useDegreasingDry cleaningGraphics artsIndustrial surface coating and solventuseNon-industrial surface coating
Miscellaneous sources
Bulk gasoline terminalsCommercial cookingGas stationsWaste disposal
Killer Smog Episodes
So, smog: how bad can it be?
1930: 63 die in Meuse Valley,Belgium
1948: 20 die in Donora, PA
The Great Smog of 1952:4000 die in London
1962: 700 die in London
These are sulfurous(“London”) Smogs
Tropospheric Air Quality 14 / 27 Photochemical Smog
The Great Smog and Environmental Epidemiology
How do we know that 4000 died due to the 1952 smog in London?
Examine correlationbetween pollutant leveland some health-basedindicator
Expect to see a lag
Should be supported bybiological plausibility andother toxicological studies(animal, clinical,biochemical)
Tropospheric Air Quality 15 / 27 Photochemical Smog
How does photochemical smog manifest?
Left: morning view; right: afternoon view (same day)
Different from sulfurous (London) smog:
favored by sunny, warm daysstrongly oxidizing, eye-wateringair pollution peaks in the afternoon
Tropospheric Air Quality 16 / 27 Photochemical Smog
Oxidation of Hydrocarbons
Explain how hydrocarbon oxidation in the presence of NO can lead tosmog formation.
NO
RO2, HO2, O3
NO2
O3
hνO + O2
Each cycle produces ozone by NO2
photodissociation
NO2hν
NO + O
O + O2 O3
Cycling rate (ie, O3 production)accelerated by O3, RO2 and HO2
Cycling via NO + O3 NO2 + O2
produces no net O3
Oxidation of hydrocarbons (RH)produces RO2
Oxidation of CO produces HO2
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Evolution of Photochemical Smog
Why does ground-level ozone peak in the afternoon?
Precursors:propene (areactive HC)and NO,generated inmorning traffic
O3 peaks afterabout 6 h
One reason:reactive VOCsare emitted inrush hour traffic
Another: OHgenerationstarts when sunrises
Tropospheric Air Quality 18 / 27 Photochemical Smog
How complicated is smogformation?
Boxed molecules arenon-radical: more stable
They are semi-volatile, cancondense to form organic PM
PAN is characteristic of smog,releases NOx downwind
Oxidation of HCs in presence ofNOx is somewhat self-catalytic
There is an NOx ‘switch’ ofabout 10 pptr
Significance of Atmopsheric Aerosol (PM)
What is the atmospheric aerosol (PM) and why is it an important partof the atmosphere?
Atmospheric composition and reactions
Cloud formation and properties
Absorption and light scattering (radiative energy balance)
Climate
Human and ecosystem health
Visibility
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PM Size Distribution
How is the size of a particle in theatmosphere related to its formationand fate?
PM Removal Processes
How long does a particle last in the atmosphere?
Ultrafine PM (Aitkennuclei) are rapidlyremoved bycoagulation
Coarse PM are rapidlyremoved bysedimentation
PM in accumulationrange last the longest(weeks to months)
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PM Composition
Chemically, what are the types of (non-biological) PM?
Carbonaceous aerosolElemental carbon (soot) directly emitted by combustion processesOrganic aerosol: direct emission of condensed phase organic material(combustion, biogenic), and some condensation of secondary organicformed by atmospheric oxidation
Nitrate aerosolFormed from dissolution/neutralization of atmospheric HNO3
Sulfate aerosolFormed from dissolution of gaseous SO3 or aqueous-phase oxidation ofdissolved SO2
Crustal materialMechanical formation (wind erosion)Consists of Si, O, Al, Fe, Mn, etc
Chloride aerosol (sea-spray)Mechanical formation in oceans (waves, bubbles)Consists of Cl, Na, K, Mg, SO4
2–, others
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Describe a ‘day in the life’ of a fine particulate.
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Effect of Pollution on Fine PM
How does pollution affect the concentration and composition of finePM?
Note that more polluted urban air has (a) more PM (7-fold) and (b)greatly increased sulfate and carbon PM fractions.
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Urban Fine PM
Describe the geographic distribution of the concentration andcomposition of urban fine PM.
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Rural Fine PM
Describe the geographic distribution of the concentration andcomposition of rural fine PM.
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