Peroxyacetyl nitrate(PAN),O3,CO,NOx,and PM10 mass,the number of fine particles larger than 3nm and 10 nm were measured onboard the RV Gisang 1 in the Yellow Sea during Nov 17th~26th,2014 and Apr 9th~May6th,2015.PAN was determined every 2 minutes by a fast chromatograph coupled with luminol chemiluminescence.Gaseous species including O3,NOx,and CO were analyzed every 1 minute(49C,42C and 48C,Thermo ElectronCorporation,Franklin,MA,USA).The mean concentrations of PM10 and the number concentrations were analyzedevery 5 minute(FH62C14,Thermo Fisher Scientific Inc.),every 1 second(CPC3772,CPC3776,TSI),respectively.PAN mixing ratios ranged from the detection limit of 0.03 ppbv up to 3.38 ppbv with a mean of 0.15 ppbv in April,0.09 ppbv in May,and 0.50 ppbv in November.The mean concentrations of O3,CO and NOx were 51.8,370 and 5.51ppbv in April,48.4,568 and 3.0 ppbv in May,and 38.3,334 and 8.1 ppbv in November.While O3 concentrations were higher over the sea particularly at lower latitudes,other species were elevated near thecoastal regions.In the Yellow Sea,however,PAN and NOx were often elevated for a short period time,which was notassociated with increase in O3.Particularly,higher concentrations of PAN were observed when O3/NOx ratio was low butCO/NOx ratio was relatively high compared to those of observed in Seoul metropolitan areas.The enhanced PAN levelpossibly indicates the influence of ship emissions in the Yellow Sea.