PM 1 – 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). 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.

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 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.

Humidity, the amount of water vapour in the air. It is the most variable characteristic of the atmosphere and constitutes a major factor in climate and weather. A brief treatment of humidity follows.

Atmospheric pressure, also called barometric pressure, force per unit area exerted by an atmospheric column (that is, the entire body of air above the specified area). Atmospheric pressure can be measured with a mercury barometer (hence the commonly used synonym barometric pressure), which indicates the height of a column of mercury that exactly balances the weight of the column of atmosphere over the barometer.

Temperature, measure of hotness or coldness expressed in terms of any of several arbitrary scales and indicating the direction in which heat energy will spontaneously flow i.e., from a hotter body (one at a higher temperature) to a colder body (one at a lower temperature).