Air Pollutants

Primary air pollutants - Materials that when released pose health risks in their unmodified forms or those emitted directly from identifiable sources.
Secondary air pollutants - Primary pollutants interact with one another, sunlight, or natural gases to produce new, harmful compounds

Primary Air Pollutants

Five major materials released directly into the atmosphere in unmodified forms.
-Carbon monoxide
-Sulfur dioxide
-Nitrogen oxides
-Hydrocarbons
-Particulate matter

Carbon Monoxide

Produced by burning of organic material (coal, gas, wood, trash, etc.)
Automobiles biggest source (80%)
Cigarette smoke another major source
Toxic because binds to hemoglobin, reduces oxygen in blood
Not a persistent pollutant, combines with oxygen to form CO2
Most communities now meet EPA standards, but rush hour traffic can produce high CO levels

Sulphur Dioxide

Produced by burning sulfur containing fossil fuels (coal, oil)
Coal-burning power plants major source
Reacts in atmosphere to produce acids
One of the major components of acid rain
When inhaled, can be very corrosive to lung tissue
London
-1306 banned burning of sea coal
-1952 “killer fog”: 4,000 people died in 4 weeks
- tied to sulfur compounds in smog

Nitrogen Oxides

Produced from burning of fossil fuels
Contributes to acid rain, smog
Automobile engine main source
New engine technology has helped reduce, but many more cars

Hydrocarbons

Hydrocarbons - organic compounds with hydrogen, carbon
From incomplete burning or evaporated from fuel supplies
Major source is automobiles, but some from industry
Contribute to smog
Improvements in engine design have helped reduce

Particulates

Particulates - small pieces of solid materials and liquid droplets (2.5 mm and 10 mm)
Examples: ash from fires, asbestos from brakes and insulation, dust
Easily noticed: e.g. smokestacks
Can accumulate in lungs and interfere with the ability of lungs to exchange gases.
Some particulates are known carcinogens
Those working in dusty conditions at highest risk (e.g., miners)
Respirable Suspended Particulate Matter (RSPM) -PM1 having size <= 1µm: effects in alveoli
-PM2.5 having size <= 2.5µm: effects trachea
-PM10 having size <= 10µm: effects in nasal part only<

Secondary Pollutants

Ozone
PAN (peroxy acetyl nitrate)
Photochemical smog
Aerosols and mists (H2SO4)

Ozone

Ozone (O3) is a highly reactive gas composed of three oxygen atoms.
It is both a natural and a man-made product that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere).
Tropospheric ozone – what we breathe -- is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOX).

PAN

Smog is caused by the interaction of some hydrocarbons and oxidants under the influence of sunlight giving rise to dangerous peroxy acetyl nitrate (PAN).

Photochemical smog

Photochemical smog is a mixture of pollutants which includes particulates, nitrogen oxides, ozone, aldehydes, peroxyethanoyl nitrate (PAN), unreacted hydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.

Aerosols and mists (H2SO4)

Aerosols and mists are very fine liquid droplets that cannot be effectively removed using traditional packed scrubbers. These droplets can be formed from gas phase hydrolysis of halogenated acids (HCl, HF, HBr), metal halides, organohalides, sulfur trioxide (SO3), and phosphorous pentoxide (P2O5).