Whenever we talk of air pollution, suspended particulate matter or PM as it is commonly referred to, is generally taken as representative of the level of pollution. In all there are eight air quality parameters, which are taken into consideration when the Air Quality Index (AQI) is calculated: Suspended particulate matter (PM2.5 and PM10), sulfur dioxide (SO2), ozone (O3), nitrogen oxides (NO2), carbon monoxide (CO), ammonia (NH3) and lead (Pb).
Particulate matter consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. It is mainly made up of sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water and allergens (fragments of pollen or mold spores).
When outdoor levels of particulate matter are high, their levels also increase indoors.
Depending on the size, there are three types of particulate matter: PM 10, PM 2.5 PM and PM 0.1.
- PM 10 are particles with a diameter of 10 microns or less (coarse particles). Sources include crushing or grinding operations and dust stirred up by vehicles on roads.
- PM 2.5 are particles with a diameter of 2.5 microns or less (fine particles).
- PM 0.1 are particles with a diameter of 0.1 microns or less (ultra-fine particles).
The sources of fine and ultra-fine particles include motor vehicles, power plants, biomass burning, agricultural burning, and industrial emissions. They remain suspended in the air for longer periods of time than coarse particles and hence, are more likely to be inhaled.
The size of the particles has a direct association with their effect on health. PM 10 particles can penetrate and remain deep inside the lungs, while PM 2.5 and PM 0.1 can penetrate the lung barrier and enter the blood system. They have more health damaging effects as they can affect all organs of the body. Fine particles (PM2.5) are the main cause of reduced visibility (haze).
As per international recommendations, both PM 10 and PM2.5 should be less than 40. For India, the PM10 levels should be less than 100 and PM 2.5 levels should be less than 60.
The larger PM 10 particles can irritate the eyes, nose and throat. PM10 mainly affects the respiratory system and may precipitate an acute asthma attack and acute exacerbation of chronic bronchitis or may cause other respiratory problems such as cough, wheeze.
The fine and ultra-fine particles also affect the heart so they may trigger an acute cardiovascular event such as heart attack or stroke or atrial fibrillation as they increase the resting blood pressure due to sympathetic overactivity and cause endothelial dysfunction and thickening of the blood.
PM 2.5 and PM 0.1 particles also have a greater association with increased mortality due to heart disease.