A system (IM) for purifying air in an indoor environment (A), with subsequent total or partial recirculation or ejection outside, comprising aspirating means (B) adapted to generate a flow (F) of air circulating along a path (P) defined by conveying means (C;C1,C2,C3), and purifying means (S;2, 3,4,5, 6,7, 10) of said air, arranged along said path (P); the mentioned purifying means (S;2, 3,4,5,6,7, 10) comprise at least one scrubbing unit (4) of said air by passing said flow (F) through a liquid with controlled pH and added ozone, and a unit (6) for generating and feeding said ozone to said scrubbing unit (4).