Environmental pollution of particulate matter

Particulate matter (PM)

-PM is a complex mixture of air borne particles that differ in size, origin and chemical composition, all of which are <10 µm in size. e.g. dust, smoke, soot. PM is composed of liquid aerosol particles and solid aerosol particles –suspended in and move with the air. Aerosols are droplets of liquids and are  generally below 5 µm size. PM is one of the six EPA ‘criteria pollutants’. PM has no fixed composition. The particles may consist either of only one chemical (e.g. sulphate, sulphuric acid, or lead oxide ) or a number of pollutants ( organic chemicals, metals, dust ). US EPA described PM pollution as ‘mixture of mixtures’. PM is among the most harmful of all air pollutants.

Sources of particulate matter

Natural particulates originate from volcanoes, dust storms, forest and grassland fires, living vegetation and sea spray. Anthropogenic particulates originate from burning fossil fuels, incinerating wastes and smelting metals.

        Types of PM particles

Primary particles are directly emitted from sources. Secondary particles form as a result of the interaction of chemicals such as SO₂, NO_x and VOCs with other compounds in the air.

Sources of PM and PM precursors

Mobile sources – Vehicles – VOCs , NO₂, PM

Stationary sources – power plants, factories – NO₂, SO₂, PM

Area sources – dry cleaners, gas stations – VOCs.

Natural sources – forest fires, volcanoes, PM

     Characteristics of particles

PM₁₀ –They are inhalable coarse particles with a diameter range 2.5 - 10 microns.They undergo rapid sedimentation. They occur near roadways and dusty industries. They bypass the body’s natural defenses in the nose and throat and enter lungs.

PM _2.5 – are fine particles with a particle diameter 2.5 microns. They remain suspended in the air and can travel extremely long distances. They are emitted from power plants, industries, and automobiles. They penetrate deeper into the lungs and damage lung tissues.

PM  _0.1 – They are ultra-fine particles or nano-particulates, smaller than 0.1 micron in diameter. They consist primarily of inorganic ions, hydrocarbons and metals. They pass from lung tissue into blood stream and circulate like oxygen molecules.

   Suspended particulate matter (SPM)

Dust is about 100 microns in diameter and they are removed in the nasal passages e.g. coal dust, cement dust. Fumes are suspended solids of less than I micron in diameter. E.g.zinc or lead oxides

Mist consist of liquid droplets with a diameter of  less than 2.0 microns.e.g. sulfuric acid mist

Smoke consists of solid particles with a diameter range of 0.05 – 1.0 microns.  They form as a result of incomplete combustion of fossil fuels. Aerosol Liquid or solid aerosols are less than 1.0 micron in diameter.

    Deposition of particulates in human body

     Coarse particles deposit in the upper respiratory tract and large airways (nose and throat) and are cleared out.Fine particles penetrate deep into the lungs and reach terminal bronchioles and alveoli. They stay there longer periods of time. Ultra-fine particles enter the blood and circulate throughout the body.

•          PM₁₀ - Inhalable particles, deposit in the extra thoracic /upper tracheo-branchial region.

•          PM _2.5 - Fine particles,deposit in deeper lung.

•          PM  _0.1 - Ultra-fine particles,pass into the circulatory system.

Sources of particulate pollution

•       Motor vehicle emissions

•       Power generation

•       Industrial combustion

•       Metal smelting

•       Wood / biomass burning

•       Construction / demolition

•       Road dust

Determinants of PM concentration – The factors like weather patterns, wind, stability (Air Vertical movement), turbulence, precipitation, topography, height of smoke stack and temperature of gases determine the concentration of particulates in a given locality of the environment..

Particle deposition in the lungs- Particle size is the most important factor for target tissue deposition.

 People at risk (sensitive human population) to particulate pollution

1. Children under 18 age.
2. Adults 65 and older.
3. Anyone with chronic lung diseases such as asthma, chronic bronchitis or emphysema.
4. Anyone with a cardiovascular disease.
5. Anyone with diabetes.

Environmental impact

•       Impairment of visibility- fine particles in the atmosphere  reduce visibility.

•       Damage to environment – particles can be carried over long distances by wind and settle on ground or water. They make lakes and streams acidic, deplete nutrients in soil and damage sensitive forests and farm crops.

•       Aesthetic effects – settling particles on statues and monuments can stain or damage stone and other materials.

Long-term human health effects  

Chronic exposure to  atmospheric particulates in human beings cause asthma, bronchitis, chronic obstructive pulmonary disease (COPD), pneumonia, upper respiratory tract or lower respiratory tract disorders and lung cancer.