Data are provided on the May 1976 northern hemispheric background concentrations of 13 halocarbons, SF6, and N2O. A model is developed that permits an easy comparison of atmospheric lifetimes, emissions, and ambient concentrations. Our measurements indicate that atmospheric levels of CCl2F2(F12) and CCl3F(F11) are consistent with an average residence time of 50 (¿33) and 36 (¿8) years respectively. The tropospheric lifetimes of reactive species such as CH3CCl3, CHCl3, and C2Cl4 are found to be 7.2 (¿1.2), 1.7 (¿0.4), and 0.4 (¿0.1) years respectively. These longer lifetimes of tropospherically reactive species are inconsistent with the existing knowledge of atmospheric chemistry. Our conservative analysis of atmospheric halocarbon data shows that average HO concentrations must be 2 to 6¿105 HO/ml instead of the accepted range of 10 to 30¿105 HO/ml. These lower HO values tend to resolve the apparent discrepancies in the biospheric budgets and distribution of chlorinated hydrocarbons and CO. The tropospheric and stratospheric implications of reduced HO levels are discussed.