Ozone (O3)

Ozone (O₃) at ground level is a secondary pollutant — it is not emitted directly but forms in the air when nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) react in sunlight. This is the same ozone that, high in the stratosphere, protects us from UV; at breathing level it is a harmful oxidant. In India's NAAQS it has an 8-hour ambient limit of 100 µg/m³ and a 1-hour limit of 180 µg/m³.

Because it is formed photochemically, ground-level ozone peaks on hot, sunny afternoons and can travel far downwind of the sources that created its precursors. It is a powerful respiratory oxidant — it inflames the airways, reduces lung function, triggers asthma attacks and, with chronic exposure, accelerates lung ageing. It also damages crops and vegetation, making it an agricultural as well as a health concern.

A recycler does not emit ozone from a stack, but contributes to its formation by emitting its precursors: NOₓ from combustion and VOCs from solvent use, pyrolysis off-gas, plastic melting and fuel/oil handling. A plastic or tyre pyrolysis unit with poor VOC capture, sited in a sunny industrial cluster, can be a meaningful contributor to local ozone even with a clean-looking stack.

Control is therefore indirect — reduce the precursors. Cut VOCs with vapour capture, closed handling of pyro-oil and solvents, and proper condensation/flaring of pyrolysis non-condensable gas; cut NOₓ through combustion tuning. Ozone is measured in ambient monitoring rather than at the stack, and an airshed already high in ozone is a reason boards push hard on VOC and NOₓ controls for new units.