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Particulate matter mainly includes dust, soot particles, volatile hydrocarbons, some sulphate and metallic residues emitted into the air by sources such as factories, power plants, vehicles, etc. PM is usually divided into different classes based on size ranging from total suspended matter (TSP) to PM-10 (particles with diameter of $10 \mu$ or less) to PM-2.5 (particles with diameter of $2.5 \mu$ or less). Smallest particles pose highest human health risk. Larger particles $(\leq 10 \mu)$ can easily be expelled from lungs through mucus but finer particles $(\leq 2.5 \mu)$ penetrate deep in lungs and can cause severe lung damage including lung cancer.