If you can smell the problem, HEPA is not going to solve it. Odour molecules, VOCs and formaldehyde are gases — orders of magnitude smaller than anything a fibre mat can intercept — and they pass through a HEPA filter as though it were not there. Gas-phase removal is entirely the carbon stage's job.
Almost every purifier sold in India contains some carbon, which is why 'has an activated carbon filter' tells you nothing useful. What varies enormously is how much: from a 40-gram carbon-impregnated mesh that is functionally decorative, to a 1.2 kg granular bed that will genuinely hold a year's worth of traffic fumes. That is the specification this page ranks on.
The three situations where it matters most in India are a home on a busy road, where NO₂ and hydrocarbon load is continuous; a newly built or newly furnished home, where engineered wood off-gasses formaldehyde for months; and a household with a smoker, where the particulate is a HEPA problem but the smell is entirely a carbon one.
One warning specific to carbon: it fails silently. When the adsorption sites are full, gas passes straight through with no drop in airflow, no rise in noise and no indicator change. Replace carbon on a calendar, not on symptoms — in Indian urban conditions that means every four to eight months, sooner than the HEPA beside it.
