These are extremely fine particulate matter (PM) particles of diameter less than 1 micron — significantly smaller than PM 2.5 (of diameter 2.5 microns) that have been at the centre of discussions on particulate matter in Delhi’s air. PM 10, PM 2.5 and PM 1 particles make up the total suspended particulate matter. These particles, byproducts of emissions from factories, vehicular pollution, construction activities and road dust, are not dispersed, and stay suspended in the air that we breathe. 1 micron is about a thousandth of a millimetre.
Why are PM 1 particles more harmful than PM 2.5 or PM 10?
The finer the particles, the more difficult they are to disperse — and the deeper they can penetrate into the blood stream, causing more harm. PM 10, which are smaller than 10 microns in diameter, enter the respiratory tract, and have been associated with risks like bronchitis, asthma, and upper respiratory tract infections. PM 10 aggravate symptoms of existing diseases more than triggering new conditions. PM 2.5 are considerably finer, penetrate into the lower respiratory tract or deeper in the respiratory tract, and the blood stream, causing cardiovascular problems.
PM 1, which are so much finer than PM 2.5, can penetrate the cardiovascular stream even further, and give rise to lasting conditions, such as predisposing people to heart diseases. Studies in the west have shown that PM 1 can lead to premature births and affect foetal development.