Particulates

Air Pollution

Particulates

– Particulates play important role in atmospheric chemistry.

– Act as catalyst to produce ozone as secondary pollutant/ health hazard

Aerosols

• small particles in our atmosphere. • are not gases.• usually solids, or tiny droplets of liquid.

sufficiently small and light • do not quickly fall out of the air under the

influence of gravity; • some aerosols remain aloft for a few

hours, while others can stay airborne for years.

Aerosol

Particulates: Sources

• Smoke and soot produced from combustion of coal, wood, petroleum

• Dust from mechanical break-up of solid

• Metallic particles such as Be, Hg, As, Pb

• Asbestos from industrial plants– Fibrous material of silicate crystals– Demolition of buildings with asbestos releases

particles ( causes scarring of lung tissue)

Metallic particles : Be, Hg, As, Pb

• BeO :used in spark plugs; – lining in high temp. furnace

• b/c of high mp. And high electrical conductivity(?)

Metallic particles Hg, As, Pb

• Hg present in fly ash– Used in manufacture of fungicide, pulp and

paper– Fly ash: when coal is burnt, most of the ash is

carried away in the exhaust gases as finely divided powder

– Contains un-burnt carbon, oxides of many metals/ Fe, Mg, Ca as well as sulfates

– Typical plant produces 1000 tons fly ash/day

dust blown aloft by winds

soot from fires,.

ash from volcanic eruptions

Aerosol

• Anthropogenic (human produced) aerosols make up about 10 percent of the amount of aerosols in our atmosphere.

• Coal-burning power plants • Internal combustion engines in cars, trucks, and

construction vehicles • Humans activities also increase the amount of

mineral dust aerosol generation. • Desertification, the removal of plants that help

prevent wind erosion of soil,..

Health Effects: irritates mucus membrane/lungs

• Asbestosis: particles with very small diameter can be trapped in the lungs and effect could be seen after ~ 30 yrs. It scars the lung tissue and thickens the lining of the lung– Leads to shortness of breath– Cancer of lower part of the lung if the

individual has the smoking habit

Health Effects: irritates mucus membrane/lungs

• Berryllium: Berylliosis– Inflammation of the respiratory system

followed by pneumonia like symptoms– Scars the tissue– Shortness of breath and coughing

Health Effects: irritates mucus membrane/lungs

• Lead poisoning: inhibit some enzyme action– Acute lead poisoning produces abdominal

pain, – nausea, – numbness of hands and feet– Muscle cramps– Brain damage

Health Effects: irritates mucus membrane/lungs

• Mercury poisoning: metabolic poison– Inhibit the enzyme system– Minamata disease produces nerve damage– Can lead to death

Control of Particulates

Removing SO2

Electrostatic precipitators

• can remove more than 99% of particulates from the gas.

• The system works by creating an electrical field to create a charge on particles which are then attracted by collection plates.

• Other removal methods include fabric filters and wet particulate scrubbers

• G G+ + e

Electrostatic precipitators

• Very voltage is applied between the discharge wire and collector plates

• Ionizes the gas molecules . Electron produced collect on the particulates

• These negatively charged particulates get attracted towards positively charged collector plates

• Collector plates are periodically shaken to remove the particulates

Gravity Settling chambers

• relies upon gravity settling to remove particles from the gas stream.

• used only for very large particles in the upper end of the super-coarse size range (approximately 75 micrometers and larger).

• a sharp decline in the use of this type of collector.

Cyclone separatorwww.epa.gov/.../matter/control/

control.htm