Regional- and national-scale emission rates of halocarbons have been a great concern in the field of global environmental studies and policy making. Emissions have been inventoried mainly by bottom-up approaches, which involve adding up emissions from various industrial sources. To verify and supplement those bottom-up inventories, top-down approaches based on measurements of air concentrations are required. In this study, aircraft monitoring over Sagami Bay, Japan, was used to estimate the emission ratios of halocarbons (perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), CFCs, hydrochlorofluorocarbons (HCFCs), and others) from Japan. The enhanced concentrations in the boundary layer of air masses having traveled over Japanese mainland were used for the calculation under the assumption that the air masses over Sagami Bay represented average emission ratios for anthropogenic halocarbons on a countrywide basis. Given their emission ratios, a single compound with a credible emission rate can yield the emission estimates for all the other compounds. When we employed an inventory-based emission estimate of HCFC-22 from the Pollutant Release and Transfer Register (PRTR) system 2002 of Japan (9.1 Gg/yr) as the reference, the estimated emission rates of HCFC-141b, HCFC-142b, CFC-12, chloroform, and trichloroethylene for 2002 were consistent with their PRTR values within 10%. Emissions of carbon tetrachloride (CCl4) and 1,1,1-trichloroethane (CH3CCl3) were much higher than their PRTR values, suggesting that their sources are not adequately accounted for in the current inventories. The present study also presents probable annual emission rates for individual HFCs and PFCs that previously had no reported estimates; for example, 4.4 Gg/yr for HFC-134a as of 2002.