air_pollutants_sources and potency.pptx

7/30/2019 Air_pollutants_Sources and Potency.pptx

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Introduction

The composition and chemistry of the atmosphere is of importancebecause of the interactions between the atmosphere and living organisms.

The composition of the Earth's atmosphere has been changed by humanactivity and some of these changes are harmful to human health, cropsand ecosystems.

Examples of problems: ACID RAINS (ACID PRECIPITATION): Deposition of acidic

components in rain, snow, fog, dew, or dry particles. Occurs when SO2and NOx are emitted into the atmosphere, undergo chemicaltransformations and are absorbed by water droplets in clouds. The dropletsthen fall to earth as rain, sn, snow or sleet.

PHOTOCHEMICAL SMOG: mixture of air pollutants, usually highlyreactive and oxidizing including: NOx, tropospheric ozone, VOCs,PAN, Aldehydes, etc.

GLOBAL WARMING: Observed increase in the average temperatureof the Earths Atmosphere and oceans in recent decades.


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Air PollutantsS.

No.

Pollutants Sources

1. Suspended particulate Matter,

SPM

Automobile, power plants, boilers, Industries requiring crushing

and grinding such as quarry, cement.

2. Sulphur dioxide Power plants, boilers, sulphuric acid manufacture, ore refining,

petroleum refining.

3. Oxides of nitrogen NO, NO2

(NOX)

Automobiles, power plants, nitricacid manufacture, also a

secondary pollutant

4. Lead Ore refining, battery manufacturing, automobiles.

5. Carbon monoxide Automobiles

6. Hydrocarbons Automobiles, petroleum refining

7. Chlorine Chlor-alkali plants.8. Fluoride Fertilizer, aluminum refining

9. Peroxyacetyl nitrate, PAN Secondary pollutant

10. Formaldehyde Secondary pollutant

11. Ozone Secondary pollutant

12. Hydrogen sulphide Pulp and paper, petroleum refining.


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Types of Air Pollution

Air Pollution various substances added to theatmosphere by natural events and human activitiesin high enough concentrations to cause harm tohumans, other organisms, or materials

Primary air pollutant a substance emitted directlyto the atmosphere

Secondary Air Pollutant a substance formed in theatmosphere as a result of reactions involvingprimary pollutants


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NAAQS Standards for Ambient Air Pollution

Pollutant[final rule cite]

Primary/Secondary

Averaging Time

Level Form

Carbon Monoxide[76 FR 54294, Aug 31, 2011]

primary

8-hour 9 ppmNot to be exceeded more thanonce per year1-hour 35 ppm

Lead[73 FR 66964, Nov 12, 2008]

primaryandsecondary

Rolling 3monthaverage

0.15 g/m3(1)

Not to be exceeded

Nitrogen Dioxide[75 FR 6474, Feb 9, 2010][61 FR 52852, Oct 8, 1996]

primary 1-hour 100 ppb98th percentile, averaged over 3years

primaryandsecondary

Annual 53 ppb (2) Annual Mean

Ozone

[73 FR 16436, Mar 27, 2008]

primaryandsecondary

8-hour 0.075 ppm(3)

Annual fourth-highest dailymaximum 8-hr concentration,averaged over 3 years

Particle Pollution

Dec 14, 2012

PM2.5

primary Annual 12 g/m3annual mean, averaged over 3years

secondary Annual 15 g/m3annual mean, averaged over 3years

primaryandsecondary

24-hour 35 g/m3 98th percentile, averaged over 3years

http://www.epa.gov/air/criteria.html
http://www.epa.gov/airquality/carbonmonoxide/http://www.gpo.gov/fdsys/pkg/FR-2011-08-31/html/2011-21359.htmhttp://www.gpo.gov/fdsys/pkg/FR-2011-08-31/html/2011-21359.htmhttp://www.epa.gov/airquality/lead/http://www.gpo.gov/fdsys/pkg/FR-2008-11-12/html/E8-25654.htmhttp://www.gpo.gov/fdsys/pkg/FR-2008-11-12/html/E8-25654.htmhttp://www.epa.gov/airquality/nitrogenoxides/http://www.gpo.gov/fdsys/pkg/FR-2010-02-09/html/2010-1990.htmhttp://www.gpo.gov/fdsys/pkg/FR-1996-10-08/html/96-25786.htmhttp://www.epa.gov/airquality/ozonepollution/http://www.gpo.gov/fdsys/pkg/FR-2008-03-27/html/E8-5645.htmhttp://www.gpo.gov/fdsys/pkg/FR-2008-03-27/html/E8-5645.htmhttp://www.epa.gov/airquality/particlepollution/http://www.epa.gov/airquality/particlepollution/http://www.epa.gov/air/criteria.htmlhttp://www.epa.gov/air/criteria.htmlhttp://www.epa.gov/air/criteria.htmlhttp://www.epa.gov/air/criteria.htmlhttp://www.epa.gov/airquality/particlepollution/http://www.gpo.gov/fdsys/pkg/FR-2008-03-27/html/E8-5645.htmhttp://www.epa.gov/airquality/ozonepollution/http://www.gpo.gov/fdsys/pkg/FR-1996-10-08/html/96-25786.htmhttp://www.gpo.gov/fdsys/pkg/FR-2010-02-09/html/2010-1990.htmhttp://www.epa.gov/airquality/nitrogenoxides/http://www.gpo.gov/fdsys/pkg/FR-2008-11-12/html/E8-25654.htmhttp://www.epa.gov/airquality/lead/http://www.gpo.gov/fdsys/pkg/FR-2011-08-31/html/2011-21359.htmhttp://www.epa.gov/airquality/carbonmonoxide/


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Air Quality Index (AQI)


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AQI Ratings

Air Quality Index(AQI) Values

Levels of HealthConcern

Colors

0 to 50 Good Green

51 to 100 Moderate Yellow

101 to 150 Unhealthy forSensitive Groups

Orange

151 to 200 Unhealthy Red

201 to 300 Very Unhealthy Purple

301 to 500 Hazardous Maroon


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AQI Calculations

If multiple pollutants are measured at a monitoring site, then thelargest or "dominant"Air Quality Indexvalue is reported for thelocation.


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WHO AIR QUALITY GUIDELINES

Substance Lowest concentration atwhich adverse effects are

observed

Duration ofexposure

Lead 0.5 g/m3 1 year

PM -- Doseresponse

SO2 500 g/m3 10 minutes

CO 30 mg/m3 1 hour

NO2 200 g/m3 1 hour

Ozone 120 g/m3 8 hours


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Primary standards provide public healthprotection, including protecting the health of"sensitive" populations such as asthmatics,children, and the elderly.

Secondary standards provide public welfareprotection, including protection againstdecreased visibility and damage to animals,crops, vegetation, and buildings.


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AIR POLLUTION SOURCES

Outdoor air quality is affected by:

Industrial or agricultural activities

Treatment of industrial effluents and domestic residues Traffic

Solid waste management

Cottage industries

Chemical incidents and spills


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Agriculture

Domestic Sources

Other Industry and waste disposal

Road Transport

Power Generation

http://www.eea.europa.eu/publications/2599XXX/page010.html
http://www.eea.europa.eu/publications/2599XXX/page010.htmlhttp://www.eea.europa.eu/publications/2599XXX/page010.html


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Basic Pollutants Toxics Air toxics (hazardous air pollutants) are known or suspected to

cause cancer or other serious health effects.

EPAs 188 hazardous air pollutants include

Benzene (motor fuel, oil refineries, chemical processes)

Perchlorethylene (dry cleaning, degreasing) Chloroform (solvent in adhesive and pesticides, by-product of

chlorination processes)

BTEX, Dioxins, PAHs, Metals (Hg, Cr)

Area/

Other

25%

Mobile

(nonroad)

20%

Mobile

(onroad)

31%

Point

24%


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Differences between toxics and criteria pollutants

Health criteria are different No AQI-like standards for toxics

Cancer/non-cancer benchmarks (long-term exposures)

Short-term exposure limits for some

A challenge to monitor Usually not available in real-time

Example: Dioxin requires 28 days of sampling to

acquire measurable amounts in ambient air

Often localized near source


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Particulate Matter Composition

Primary PM (directlyemitted)

Suspended dust

Sea salt

Organic carbon

Elemental carbon

Metals from combustion

Small amounts of sulfateand nitrate

Secondary PM (precursor gases

that form PM in the atmosphere)

Sulfur dioxide (SO2): forms

sulfates

Nitrogen oxides (NOx): forms

nitrates

Ammonia (NH3): forms ammoniumcompounds

Volatile organic compounds

(VOCs): form organic carbon

compounds

PM is composed of a mixture of primary and secondarycompounds.


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NaCl salt is found in PM near seacoasts and after de-icing materials areapplied

Organic Carbon (OC) consists ofhundreds of separate compoundscontaining mainly carbon, hydrogen,and oxygen

Elemental Carbon (EC) composedof carbon without much hydrocarbonor oxygen. EC is black, often called

soot.

Liquid Water soluble nitrates,sulfates, ammonium, sodium, otherinorganic ions, and some organicmaterial absorb water vapor from theatmosphere


Chow and Watson (1997)

Geological Material suspended

dust consists mainly of oxides of Al,

Si, Ca, Ti, Fe, and other metal

oxides

Ammonium ammonium bisulfate,

sulfate, and nitrate are most

common

Sulfate results from conversion of

SO2 gas to sulfate-containingparticles

Nitrate results from a reversible

gas/particle equilibrium between

ammonia (NH3), nitric acid (HNO3),

and particulate ammonium nitrate

Most PM mass in urban and nonurban areas is composedof a combination of the following chemical components


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PM Emissions Sources

Point generally a major facility emitting pollutants from identifiablesources (pipe or smoke stack). Facilities are typically permitted.


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PM Emissions SourcesArea any low-level source of air pollution released over

a diffuse area (not a point) such as consumer products, architectural

coatings, waste treatment facilities, animal feeding operations, construction,

open burning, residential wood burning, swimming pools, and charbroilers


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PM Emissions SourcesMobile

On-road is any moving source of air pollution such as cars, trucks,motorcycles, and buses

Non-road sources include pollutants emitted by combustion engines on

farm and construction equipment, locomotives, commercial marine

vessels, recreational watercraft, airplanes, snow mobiles, agricultural

equipment, and lawn and garden equipment


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PM Emissions SourcesNatural biogenic and geogenic emissions from wildfires, wind blown

dust, plants, trees, grasses, volcanoes, geysers, seeps, soil, and

lightning


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ORIGIN OF THE ATMOSPHERIC AEROSOL

Soil dustSea salt

Aerosol: dispersed condensed matter suspended in a gasSize range: 0.001m (molecular cluster) to 100m (small raindrop)

Environmental importance: health (respiration), visibility, radiative balance,cloud formation, heterogeneous reactions, delivery of nutrients


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Particulate Matter Chemistry

Coagulation: Particles collide and stick together.

Condensation: Gases condense onto a small solid particle

to form a liquid droplet.

Chemical Reaction: Gases react to form particles.

Cloud/Fog Processes: Gases dissolve in a water droplet andchemically react. A particle exists when the water evaporates.

Sulfate


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NOx

Ammonia

VOCs


Primary Particles(directly emitted) Secondary Particles(from precursor gases)

Other(sea salt)

Crustal(soil,dust)

OrganicCarbon

Carbon(Soot)

SO2

AmmoniumSulfate

AmmoniumNitrate

Metals

Composition of PMtells us aboutthe sources and

formationprocesses

Gas

Particle


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Sulfur Dioxide

Sulfur dioxide (SO2) belongs to the family of sulfur oxide (SOx)

gases.

Gases are formed when fuel containing sulfur (mainly coal and oil) is

burned and during metal smelting and other industrial processes.

Affects the respiratory system

Reacts in the atmosphere to form acids, sulfates, and sulfites

Contributes to acid rain

Low crown densityof spruce trees

German sandstone

statue, 1908, 1969

Impact of low soil

pH on agriculture

in Victoria


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Sulfate Chemistry Virtually all ambient sulfate (99%)is secondary, formed within theatmosphere from SO2 during thesummer.

About half of SO2 oxidation to sulfate

occurs in the gas phase throughphotochemical oxidation in the daytime.NOx and hydrocarbon emissions tend toenhance the photochemical oxidation rate.

At least half of SO2 oxidation takes placein cloud droplets as air molecules react in clouds.

Within clouds, soluble pollutant gases, such as SO2, are scavenged by waterdroplets and rapidly oxidize to sulfate.

Only a small fraction of cloud droplets deposit out as rain; most dropletsevaporate and leave a sulfate residue or convective debris.

Typical conversion rate 1-10% per hour

Husar (1999)

Heterogeneous Oxidation

Chemistry(2 of 4)


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Mechanisms of Converting S(IV) toS(VI)

Why is converting to S(VI) important?

It allows sulfuric acid to enter or form within cloud drops

and aerosol particles, increasing their acidity

Mechanisms

1. Gas-phase oxidation of SO2(g) to H2SO4(g) followed by

condensation of H2SO4(g)

2. Dissolution of SO2(g) into liquid water to form

H2SO3(aq) followed by aqueous chemical conversion of

H2SO3(aq) and its dissociation products to H2SO4(aq) and

its dissociation products.


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Nitrate Chemistry NO2 can be converted to nitric acid (HNO3) by reaction with hydroxyl

radicals (OH) during the day.

The reaction of OH with NO2 is about 10 times faster than the OH reaction

with SO2.

The peak daytime conversion rate of NO2 to HNO3 in the gas phase isabout 10% to 50% per hour.

During the nighttime, NO2 is converted into HNO3 by a series of

reactions involving ozone and the nitrate radical.

HNO3 reacts with ammonia to form particulate ammonium nitrate

(NH4NO3).

Thus, PM nitrate can be formed at night and during the day; daytime

photochemistry also forms ozone.


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Winds Clouds, fog Winds Temperature

Temperature Temperature Precipitation Relative humidity

Solar radiation Relative humidity Winds

Vertical mixing Solar radiation

condensation and

coagulation

photochemical production

cloud/fog processes

gases condense onto particles

cloud/fog processes Measurement

Issues Inlet cut points Vaporization of nitra

H2O, VOCs Adsorption of VOCs Absorption of H2O

transport

sedimentation(dry deposition)

wet deposition

Mechanical Sea salt Dust

Combustion Motor vehicles Industrial Fires

Other gaseous

Biogenic Anthropogenic

Particles NaCl Crustal

Particles Soot Metals OC

Gases NOx SO2 VOCs NH3

Gases

VOCs NH3 NOx

SourcesSample

CollectionPM Transport/LossPM

FormationEmissions

Chemical Processes

eteorological Processes



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Phenomena Emissions PM Formation PM Transport/Loss

Aloft PressurePattern No direct impact. No direct impact. Ridges tend to produce conditions conducive for accumulat ion of PM2.5.Troughs tend to produce conditions conducive for dispersion and removal of PM andozone.In mountain-valley regions, strong wintertime inversions and high PM2.5 levels may not bealtered by weak troughs.High PM2.5 concentrations often occur during the approach of a trough from the west.

Winds andTransport

No direct impact. In general, stronger winds dispersepollutants, resulting in a less idealmixture of pollutants for chemicalreactions that produce PM2.5.

Strong surface winds tend to disperse PM2.5 regardless of season.Strong winds can create dust which can increase PM2.5 concentrations.

TemperatureInversions

No direct impact. Inversions reduce vertical mixing andtherefore increase chemical

concentrations of precursors. Higherconcentrations of precursors canproduce faster, more efficientchemical reactions that producePM2.5.

A strong inversion acts to limit vertical mixing allowing for the accumulation of PM2.5.

Rain Reduces soil and fire emissions Rain can remove precursors ofPM2.5.

Rain can remove PM2.5.

Moisture No direct impact. Moisture acts to increase theproduction of secondary PM2.5including sulfates and nitrates.

No direct impact.

Temperature Warm temperatures are associatedwith increased evaporative,biogenic, and power plantemissions, which act to increasePM2.5. Cold temperatures can alsoindirectly influence PM2.5concentrations (i.e., home heatingon winter nights).

Photochemical reaction ratesincrease with temperature.

Although warm surface temperatures are generally associated with poor air qualityconditions, very warm temperatures can increase vertical mixing and dispersion ofpollutants.Warm temperatures may volatize Nitrates from a solid to a gas.Very cold surface temperatures during the winter may produce strong surface-basedinversions that confine pollutants to a shallow layer.

Clouds/Fog No direct impact. Water droplets can enhance theformation of secondary PM2.5.Clouds can limit photochemistry,which limits photochemicalproduction.

Convective clouds are an indication of strong vertical mixing, which disperses pollutants.

Season Forest fires, wood burning,

agriculture burning, field tilling,windblown dust, road dust, andconstruction vary by season.

The sun angle changes with season,

which changes the amount of solarradiation available forphotochemistry.

No direct impact.

Meteorology

How weather affects PM emissions, formation, and transport


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ANNUAL MEAN PARTICULATEMATTER (PM) CONCENTRATIONS AT U.S. SITES,1995-2000

NARSTO PM Assessment, 2003

PM10 (particles > 10m) PM2.5 (particles > 2.5m)

Red circles indicate violations of national air quality standard:50g m-3 for PM10 15g m-3 for PM2.5


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AEROSOL OPTICAL DEPTH (GLOBAL MODEL)

Annual mean


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AEROSOL OBSERVATIONS FROM SPACE

Biomass fire haze in central America yesterday (4/30/03)

Fire locationsin red

Modis.gsfc.nasa.gov


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BLACK CARBON EMISSIONS

Chin et al. [2000]

DIESEL

DOMESTICCOAL BURNING

BIOMASSBURNING


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RADIATIVE FORCING OF CLIMATE, 1750-PRESENT

Kyoto also failed to address two major pollutants that have an impact on warming:black soot andtropospheric ozone.Both are proven health hazards.Reducing both would not only address

climate change, but also dramatically improve people's health. (George W. Bush, June 11 2001 RoseGarden speech)

IPCC [2001]

P i l I H H l h d MORE


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Particles Impact Human Health and MORE


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Nitrogen Oxides

Nitrogen oxides, or NOx, is the generic term for a group of highlyreactive gases, all of which contain nitrogen and oxygen in varyingamounts.

Nitrogen dioxide is most visually prominent (it is the yellow-browncolor in smog)

The primary man-made sources of NOx are motor vehicles;electric utilities; and other industrial, commercial, and residentialsources that burn fuels

Affects the respiratory system

Involved in other pollutant chemistry

One of the main ingredients in the formation of ground-level ozone

Reacts to form nitrate particles, acid aerosols, and NO2, which also causerespiratory problems

Contributes to the formation of acid rain (deposition)


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NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE

Fossil Fuel

23.1

Aircraft0.5

Biofuel

2.2

BiomassBurning

5.2

Soils5.1

Lightning5.8

Stratosphere0.2


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NOx

Oxides of nitrogen formed in combustion processes are usuallydue to either thermal fixation of atmospheric nitrogen incombustion air or to the conversion of chemically boundnitrogen in the fuel. Thermal fixation occurs when combustiontemperature is above 1600C. For natural gas and distillate oilnearly all NO results from thermal fixation. For residue oil and

coal, the contribution to NO emission from fuel bound nitrogenmay be significant.

The concentration of NOx formed increases with increase in

excess oxygen maintained in the combustion process and withthe increase in temperature of the furnace. For coal basedthermal power plants in India, it ranges between 100 and 200mg/Nm3 in the flue gas. In the case of natural gas and liquidfuels, the emission limits for flue gases prescribed in Europeancountries is in the range of 200 - 400 mg/Nm3.


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Must make NO2

To make significant amounts of ozone musthave a way to make NO2 without consumingozone

Presence of peroxy radicals, from theoxidation of hydrocarbons, disturbs O3-NO-NO2 cycle

NO + HO2 NO2 + OH

NO + RO2

NO2 + RO

leads to net

production of ozone


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The Hydroxyl Radical

produced from ozone photolysis

for radiation with wavelengths less than 320 nm:

O3 + hv O(1D) + O2

followed by

O(1D) + M O(3P) + M (+O2O3) (~90%)

O(1D) + H2O 2 OH (~10%)

OH initiates the atmospheric oxidation of a wide range of compounds in theatmosphere

referred to as detergent of the atmosphere

typical concentrations near the surface ~106 - 107cm-3

very reactive, effectively recycled


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THE OH RADICAL: MAINTROPOSPHERIC OXIDANT

Primary source: O3 + hn O2 + O(1D) (1)

O(1D) + M O + M (2)

O(1D) + H2O 2OH (3)

Sink: oxidation of reduced species leads to

HO2(RO2) production

CO + OH CO2 + H

CH4 + OH CH3 + H2O

HCFC + OH

Global Mean [OH] = 1.0x106 molecules cm-3

MajorOH sinks


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An example of gridded NOx emissions


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Mapping of Tropospheric NO2

From the GOME satellite instrument (July 1996)


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Ozone

Colorless gas Composed of three oxygen atoms

Oxygen molecule (O2)needed to sustain life

Ozone (O3) the extra oxygen atom makes ozonevery reactive

Secondary pollutant that forms from precursor gases

Nitric oxide combustion product

Volatile organic compounds (VOCs) evaporativeand combustion products


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Ozone Precursor Emissions

Man-made sources

Oxides of nitrogen (NOx) through combustion

VOCs through combustion and numerous other

sources

Natural sources (biogenic)

VOCs from trees/vegetation

NOx from soils (Midwest fertilizer)

Concentration depends on Source location, density, and strength

Meteorology

Emissions Chemistry

Meteorology


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Solar radiation and chemistry

The reaction that produces ozone in theatmosphere:

O + O2 + M O3 + M

Difference between stratospheric andtropospheric ozone generation is in thesource of atomic O

For solar radiation with a wavelength of lessthan 242 nm:

O2 + hv O + O


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Solar radiation and chemistry

Photochemical production of O3 in troposphere tied to NOx (NO +

NO2)

For wavelengths less than 424 nm:

NO2 + hv NO + O

But NO will react with O3

NO + O3 NO2

Cycling has no net effect on ozone


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Tropospheric Ozone Photolysis

Troposphere ozone photolysis takes place in a narrow UV window

(300-320 nm), NO2 broadly below 428

30o equinoxmiddaySolar spectrum


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Ozone ChemistrySummary of ozone chemistry

NO2 + Sunlight NO + O Production

O+ O2 O3 Production

NO + O3 NO2 + O2 Destruction

VOC + OH RO2 + H2O Production of NO2 without the

RO2 + NO NO2 + RO Destruction of O3

Emissions Chemistry

Meteorology

Key processes

Ample sunlight (ultraviolet) High concentrations of precursors (VOC, NO, NO2)

Weak horizontal dispersion Weak vertical mixing

Warm air

RO=Reactive Organic compound such as VOC


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Day and Night Chemistry


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Carbon Monoxide

Odorless, colorless gas

Caused by incomplete combustion of fuel

Most of it comes from motor vehicles

Reduces the transport of oxygen through the

bloodstream

Affects mental functions and visual acuity, evenat low levels


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What breaks the cycle?

Cycle terminated byOH + NO2 HNO3

HO2 + HO2 H2O2

Both HNO3 and H2O2 will photolyze or react with OH to, in

effect, reverse these pathways but reactions are slow (lifetime of several days)

both are very soluble - though H2O2 less-so

washout by precipitation

dry deposition

in PBL they are effectively a loss

situation is more complicated in the upper troposphere

no dry deposition, limited wet removal


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LEAD (Pb) IN AIR

SOURCES

Tetraethyl lead in petrol

Mining and smelting of lead ores

Industry

Waste incineration

Dust (e.g. homes with old lead-based paint, battery recycling,smelters)


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CARCINOGENS IN AIR

Pollutant System affected

Arsenic Lung

Benzene Leukaemia

Chromium VI Lung

Nickel Lung

PAHs Lung

Vinyl chloride liver

Radon Lung, Gastrointestinal

air_pollutants_sources and potency.pptx

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