Plant-microorganisms interaction promotes removal of air pollutants in Milan (Italy) urban area.

•Plants and phyllosphere microorganisms contribute to reduce air pollution by the adsorption and biodegradation of pollutants.•Hydrocarbon degrading bacteria are positively selected on plant leaves when the air pollution reaches its peak.•The magnitude of contaminant removal by biodegradation on urban tree leaves is likely to have huge impacts at city scale.