Ozone(O3)and Secondary organic aerosol(SOA)are important pollutants in theurban atmosphere.Benzene is one of the most important aromatic precursors,which couldproduce O3 and SOA in the presentence of NOx and UV light.A series of experiments was carriedout to study the effect of NaCl seed particles and humidity on O3 and SOA formation frombenzene in an indoor smog chamber.The results show that the peak O3 concentration decreasedwith the increase of relative humidity or NaCl particles.The peak O3 greatly reduced about 53%as RH increased from 9%to 87%with the close initial concentrations of NaCl(about 26 μg/m3).The peak O3 decreased by 47%as initial NaCl concentrations increased from 20.0 μg/m3 to 84.5μg/m3 at about 73%RH.The correlation between variations of liquid water and RH or NaCl wasinvestigated.It shows that the heterogeneous reaction of N2O5 with the liquid water(aqueous NaCl)is the major reason that account for the decrease of O3 under different RH and NaCl conditions.Unlike the effects of NaCl to O3 formation,the yield of SOA increased with increasing liquidwater content,due to the increase of RH or NaCl concentrations.The intensity of the bands ofO–H,C=O,C–O,and C–OH from SOA samples all enhanced with the liquid water content as theincreasing RH and NaCl seed aerosol in the photooxidation of benzene.