A new mechanism of ozone loss is found in the sub-tropical marine boundary layer over the north Pacific. This ozone destruction occurs just after sunrise (hereafter Sunrise Ozone Destruction, SOD) and is commonly found throughout the year. SOD is a predominant ozone loss mechanism in winter, which takes place after sunrise in a few hours with 1~2 ppbv of ozone depletion for 40~50 ppbv of background ozone, while, in summer, SOD is weaker than in winter with small ozone depletion for 10~20 ppbv of background ozone. In summer, daytime ozone destruction (hereafter, DOD) associated with UV photolysis and subsequent HOx reaction is more active. Since DOD is not active in early morning, SOD should be a new ozone loss mechanism. After demonstrating the observational findings, halogen chemistry associated with sea-salt aerosols is described as a possible mechanism. ¿ 1999 American Geophysical Union