Definition of air pollution:

It is the presence of one or more air contaminants; [such as dust. gas, mist, odor, smoke, or vapor], in sufficient quantity, of such characteristics, and of such duration as to be or to threaten to be injurious to human, plant, or animal life, or to property, or which reasonably interferes with the comfortable enjoyment of life or property.

  Definition of atmosphere:

      It is the air envelop around the earth, and is divided into four layers:

      Troposphere            0 - 12       kilometer

      Stratosphere             12-52        kilometer      

      Mesosphere              52 - 90     kilometer

     Thermosphere           > 90         kilometer

  The forms of air pollutants:

      It is small solid particles created by the break up of larger masses through mechanical processes,

Particle size ranges from 1 to 1000 µm       


      They are fine solid particles formed by the condensation of vapors of solid materials,   

      Particle size ranges from 0.03 to 1.0 µm


      It is fine particles resulting from the incomplete combustion of organic substances such as coal,                wood,  or tobacco .It consists mainly of carbon and other combustible materials,

      Particle size ranges from 0.5 to 1.0 µm.


        It consists of finely divided, noncombustible particles contained in gas that arise from coal combustion,

        Particle size ranges from 1 to 1000 µm.

       It consists of liquid particles formed by atomization of parent liquids

       Particle size ranges from 10 to 1000 µm.

      It consists of liquid droplets formed from vapor condensation,

      Splashing, or from the enactment of chemical reactions,

      Particle size is less than 10 µm.

  Types of sources of pollution:

   1. Anthropogenic Source:

      It is the source of air pollution from man made activities

   2. Biogenic Source:

      It is the source of air pollution from animals or plants.  

 Planetary Boundary Layer PBL :

It is the region of the earth's atmosphere from the surface up to 1500 m, within which the great majority of the emission, transport, reactions, and deposition occur. The reminder of the atmosphere is called the free atmosphere.

  Ambient air pollutants


Characteristics Or Examples


Six major pollutants for which ambient air standards have been set to protect human health and welfare.

Criteria Pollutants

A major component of photochemical smog formed from NO,, VOCs, and oxygen in presence of sunlight and heat. Motor vehicles are a major generator of NO, and VOCs.

Ozone (O3)

Produced by combustion of fossil fuel and biomass. By itself, CO represents more than 50% of all air pollutants. Motor vehicles are the major source of CO, especially in cities.

Carbon Monoxide CO


An acid precursor converted to acid under moist conditions or to sulfate in dry. Both the acid and sulfate are particulates and major Components of haze. Fossil fuel burning power plants produce 75%.

Sulfur Dioxide SO2


Acid precursors converted to acid under moist conditions or to nitrate in dry. Both acid and nitrate are particulates and components of haze. In cities, motor vehicles generate about 60% of NOx.

Nitrogen Oxides  NOx


Emitted as particulates from metal mining and processing facilities, and by combustion processes.

Lead pb


Solid particles composed of one or several chemicals. There are many sources. Those from combustion processes pose the highest concern.

 Particulates PM10


The 189 haps do not have ambient air standards. Instead, emissions controls are used. About 70% are also vocs.

 Hazardous Air  Pollutants (Haps)


Examples are benzene, formaldehyde, vinyl chloride.


Examples are asbestos and metals (such as cadmium and mercury).



Organic chemicals that evaporate easily. Some significantly contribute to smog.




     1-Carbon Monoxide CO:

-It is a colorless, odorless flammable, poisonous gas.

-It is a product of incomplete combustion.

-It accounts for 50% of air pollution.

     Sources of CO :

 -It is produced when carbonaceous fuels are burned under less than ideal conditions.

 -The natural anaerobic decomposition of carbonaceous material by soil microorganisms release methane to the atmosphere. Atmospheric oxidation methane gas produces CO.

            CH4 + OH →CH3 + H2O

    This reaction is followed by series of 39 reactions, which can be simplified by:

            CH3 + O2 + sunlight] → CO + H2 + OH

Motor vehicle (77%), fossil fuel burning for electricity and heat, industrial processes, solid waste disposal, cigarette smoke, and miscellaneous burning.

     The two most probable sinks for CO are:

 -reaction with hydroxyl radical to form Co2

      OH + C→ CO2 + H

 - Removal by soil microorganisms.

  How can CO being reduced:

 -Cars and trucks owners need to maintain their vehicles.

 -Prohipting open burning of trash and garbage.

 -Maintaining high burning efficiency.


       It causes headache, dizziness, drowsiness.

   Air quality standards

     10 ppm for 8 hours,

     35-40 ppm for 1 hour

   2-Nitrogen Oxides NOx :


 There are several nitrogen oxides NOx   gases; nitric oxides NO, nitrogen dioxide NO2   , nitrous oxides N2O , referred to as NOx..

NOx is composed of varying components of nitrogen and oxygen.


-Bacterial action in the soil releases nitrous oxide N2O to the atmosphere.

(Especially large amounts after nitrogen fertilizers additions to soil)

-Microorganisms decomposing vegetation release nitrogen oxides.

 -Lightning and volcanoes emit NOx.

- In the upper troposphere and stratosphere, atomic oxygen resulting from ozone dissociation reacts with nitrous oxide to form nitric oxide:

          N2O    +   O   -—-» 2 NO


- Nitric oxide further reacts with ozone to form nitrogen dioxide:

      NO   +   O3   -—-» NO2   +   O2

- Combustion process accounts for 96% of the anthropogenic sources of nitrogen oxides.

-Vehicles emissions increase the level of NOx.

- Ultimately, the NO2 is converted to either nitrite or nitrate in particulate form. The particulates are then  washed out by precipitation. The dissolution of nitrate in a water droplet allows for the formation of       nitric acid HNO3.


-It irritates eyes, lungs, and can lower the resistance to infection.

-It is poisonous to plant life (sometimes it has beneficial effects, as the nitrogen is an important plants nutrient.

-It reacts with VOCs in the presence of sunlight to produce photochemical oxidants that have adverse effects consequences.

-It is involved in the three major global changes problems but to a less extent than SO2.

   How can NOx . being reduced:


      NOx is harder to be controlled because direct formation of NOx due to reaction between nitrogen and                     oxygen at high temperature

-Cars and trucks owners need to maintain their vehicles.

 -Preheating open burning of trash and garbage.

     Air quality standards

       0.053 ppm annual

       Non for 1 hour

    Volatile Organic Compounds VOCs :


They are non methane hydrocarbons [NMHC] such as alkanes, alkenes, and aromatics, and other organic compounds that readily vaporize.

    Sources of VOCs


      Solvents, painting, oil refinery, aerosol sprays, and motor vehicles, uncompleted fossil fuels combustion.

      Transportation sector is responsible about 33% of the anthropogenic source pf VOCs.

      3-Ozone O3


-It is a secondary pollutant

-It is a more reactive chemical than oxygen.

-It is found in smog, which is called photochemical smog, because of summer sun role in its formation.

     Sources of ozone O2


      -VOCs,  Nox , react with atmospheric oxygen in summer to form ozone.

       VOCs +  Nox  + sunlight → photochemical smog (O3) +etc

       -The NO, NO2, O3 photochemical reaction sequence:


       N2 + O2 → NO+ O2 → NO2 (in sun light) → NO+ O


       O+ O2      → O3  + NO → NO2 + O2  


      -Vehicles emissions are the main sources of Nox & VOCs.


  -It irritates the eyes, nose, throat and lungs.

 -It causes inflammation of the bronchial tubes.

 -It increases susceptibility to infection.

 -It adversely affects plants (sensitive crops are damaged at 0.05 ppm).

  How to control O3 formation:

    Maintaining and control the motor vehicles to reduce the emission of VOCs & Nox.

   Air quality standards

     0.08 ppm for 8 hours


 -Methane [which results from decaying of organic matters], and [unsaturated hydrocarbons, which are released from living plants], are the two major hydrocarbons emitted by natural sources

 -The major anthropogenic sources are; partially burned gasoline, and incinerators emissions [38% and 23% of the global emissions, respectively].

-Gasoline evaporation, refinery losses, and solvent evaporation account for another 27 % of anthropogenic sources of hydrocarbons.

-Many hydrocarbons are converted to other organic compounds in the presence of nitrogen oxides. Ultimately, they may be converted to particles.

   4-Particulates PM10

-It varies in chemical composition.

-It may contain sulfate or lead.

-Another contains sulfate, nitrate, metals, dust or biological matter.

-Some sulfur dioxide and nitrogen oxide emissions are converted to Particulates.

-The HAP asbestos is also particulate pollutant.

-VOCs can directly condense into Particulates


-Sea salt, soil dust, volcanic particles, and smoke from forest fires, rust, versus & bacteria account for air pollution by Particulates

 -Anthropogenic emissions from fossil fuel burning and industrial processes account for emissions of Particulates.

 -The major anthropogenic sources are; motor vehicles, electric power plants, industrial process, combustion process power plants and incinerators inefficient burning.

-Secondary sources of particulate include the conversion of H2S, SO2, N0x, NH3 and hydrocarbons

 -Dust particles that are entrained by wind and carried over long distances tend to sort themselves out to the sizes between 0.5 and 50 micron in diameter.

 -Sea salt nuclei have sizes between 0.05 and 0.5 micron.

 -Particulate formed as a result of photochemical reactions tends to have very small diameters [less than 0.4 micron].

-Smoke and fly ash particles cover a wide range of size from 0.05 to 200 micron or more.

-Particle mass distribution in urban atmosphere generally exhibit two maxims one is between 0.1 and 1 micron in diameter, and the other is between 1 and 30 micron.



     Health impacts:


-It can cause respiratory problems.

-It affects breathing and can cause lung damage.

-Coal workers and textile workers suffer from black and brown lung disease respectively.

- Workers exposed to airborne asbestos suffer from lung cancer.

-It affects nervous system and blood forming system.

-It damage plant tissues and reduce photosynthes process.

-In addition to Health impacts particulate contribute to the smog seen in many cities.

-In coastal area particulate contains high level of chloride which can corrode local building.

    Air quality standards

       150 µg/m3 for 24 hours.

       50 µg/m3 annual


   5-Sulfur dioxides SO2.:


 -It is a colorless gas with sharp odor.

-It accounts for 18% of all air pollution.


-Sulfur oxides may be both primary and secondary pollutants. Power plants, industry, volcanoes, and the ocean emit SO2 and SO3 directly as primary air pollutants.

- The combustion of fossil fuels containing sulfur yield sulfur dioxide in direct proportion to the sulfur content of the fuel:

S   +   O2    -—-»     SO2.

Because of the combustion efficiency, about 5% of the sulfur in the fuel ends up in the ash.

-Metal smelters, pulp & paper mills, and oil refineries

-Biological decay processes and some industrial sources emit hydrogen sulfate H2S which is oxidized to form the secondary pollutant S02:

             H2S + O3      -—-»   H2O + SO2

-Motor vehicles accounts for a small amounts of SO2

    Fate of SO2

-The ultimate fate of most of SO2 in the atmosphere is Conversion to sulfuric acid and sulfate salts, which are removed by Sedimentation or by washout with precipitation. The Conversion may be catalytic oxidation or photochemical oxidation.

  -Catalytic oxidation is most effective if water droplets containing Fe3+ Mn2+ or NH3 are present:

   2 SO2 +2 H2O -—-»    2H2SO4

-Photochemical oxidation takes place at low relative humidity:

First step photo excitation of SO2


SO2+ sunlight -—> SO2




SO2♦     +      O2 -—-»   SO3   +    O


SO3+ H2O —>H2SO4


The last reaction in a large part accounts for acid rain [i.e. precipitation with pH value less than 5.6].


-It reacts with the moisture in the eyes and lungs and other membranes to form strongly irritated acid.

-It can aggravate already existing respiratory or heart disease.

- SO2 in foods can trigger allergic reaction and asthma in sensitive individuals.-It can damage plants and trees.

-SO2 is converted into sulfuric acid or sulfate particulates which are directly involved in the three major global changes problems, acidic deposition, stratospheric ozone depletion ( whereby sulfate particles in the stratosphere provide surfaces on which ozone destroying destruction occur,  and the antiwarming influence exert in global climate change.

     How can SO2 being reduced:

      CAA 1970, 1976 control the emission of SO2 from coal burning, electric power plants and other                      sources.

      -Using fuel containing lower amounts of sulfur.

     Air quality standards

        0.14 ppm for 24 hours,     

        0.03 ppm annual

    6-Lead ( pb):

        It is a highly useful metal, has been mined for thousand of year.


-  The primary natural sources are volcanic activity and airborne soil. 

-  Smelters and refining processes, as well as incineration of lead containing wastes are major point sources of lead.            

-  Approximately from 70 to 80 percent of the lead which used to be added to gasoline was discharged to the atmosphere.

-  Submicron lead particles which are formed by volatilization and subsequent condensation, attach to larger particles or they form nuclei before they are removed from the atmosphere.

- Once lead particles attained a size of several microns, they either settle down or washed out by rain.


      Health impacts:

      Lead is toxic for nervous system.

   Air quality standards

      1.5 µg/m3 for 3 month

   Summary of Fates of Selected Gaseous Air Pollutants

  Sulfur dioxide:

 In atmosphere: oxidation in gas and liquid phase to sulfate salts which are removed by sedimentation or by washout with precipitation.

     In Soil: microbial degradation, physical and

     Chemical reaction, absorption.

     Vegetation: sorption on surfaces

     Oceans, lakes: absorption.

     Hydrogen sulfide: oxidation to sulfur dioxide.


     Chemical react ion on vegetation, soil, snow and ocean surfaces and converted to NO2.

   Nitrous Oxide (N2O):

     In Soil: microbiological destruction

     Stratosphere:  photo dissociation to nitric oxides NO

     Ocean: absorption

   Nitrogen dioxide NO2:

   In soil: chemical reaction

   Vegetation:  sorption, stomata uptake.

    Chemical reaction: NO2 is converted to either nitrite or nitrate in particulate form, washed out by precipitation.

     The dissolution of nitrate in a water droplet allows for the formation of nitric acid HNO3


        In gas and liquid phase: Chemical reaction converted to ammonium,

        That washout with precipitation.

 Carbon monoxide:

       In stratosphere: reaction with Hydroxyl radical to form CO2.

       In soil: microbiological activity.

       Carbon dioxide:

       Vegetation: photosynthesis absorption

       Ocean: absorption

    Methane CH4:

      In soil: microbiological activity

     Vegetation: chemical reaction, bacterial action

      In Troposphere and stratosphere: chemical reaction and conversion to CO.


     Chemical reaction to particulates

      In soil: microbiological activity

     Vegetation: Absorption

   Hazardous Air Pollutants:

     -The 1990 CAA amendments regulate 189 HAPs.

     -About 70% of the 189 HAPs are also VOCs.


    Table 2 shows some examples of organic & inorganic HAPs.

Representative Sources Or Uses

 Organic Chemicals

Gasoline, cigarette smoke


Gasoline, motor vehicle exhaust, cigarette smoke, paints


 Automobile antifreeze, brake fluid

Ethylene glycol

Windshield antifreeze, solvent


Formed during water chlorination and other chlorine uses



 Methyl bromide

Particleboard and plywood, building insulation,    cosmetics




Manufacture of plastics, rubbers, adhesives, cushions


Manufacture of plastics, new automobile interiors

Vinyl chloride


Representative Sources Or Uses

Inorganic Chemicals

Fibrous mineral once widely used to fireproof materials


Nonmetallic element used in metal alloys and glass making


Electroplating, NiCad batteries, pigment, plastic stabilizer


Electroplating auto parts and bathroom fixtures, also


chemical catalyst


In thermometers, lamps, dental amalgams


Electroplating, in alloys; chemical catalyst


  Impacts of HAPs

     Most of the HAPs have health impacts:

     Benzene can irritate eyes, skins and cause headache, dizziness                                   

     Formaldehyde can irritate eyes and lungs and at high doses, is an animal carcinogen.

    Chloroform can damage the kidneys and liver and at high doses, is an animal carcinogen.

    Cadmium is a highly toxic metal that concentrate at plants, sell-fish, and animal kidneys and liver.

    Mercury it is especially toxic after conversion to methyl mercury by bacteria.