Reactivity of NaClO2 and HA-Na in air pollutants removal: active species identification and cooperative effect revelation

•The generation/release of ClO2 from NaClO2 were affected by pH, temperature and standing time.•HA-Na was a good cooperator for NaClO2 in removal of SO2, NO and Hg0.•The removal efficiencies of SO2, NO and Hg0 by NaClO2/HA-Na were 100%, 95.3% and 100% respectively.•The products were characterized as NaCl, HA, Na2SO4, NaNO3, HgSO4, Hg(NO3)2 and HgCl2.