Bond contribution values, used to estimate Henry's law constant (HLC) (air-to-water partition coefficient) from chemical structure, have been determined for 59 chemical bonds by a least-square analysis of known HLCs for 345 organic compounds. A correlation coefficient (r2) of 0.94 was determined for the relationship between known LWAPCs (log water-to-air partition coefficients) and bond estimated LWAPCs for the 345 compound data set. The correlation coefficient increases to 0.97 when quantified correction factors are applied to selected chemical classes. The ability of the bond method to estimate LWAPCs is demonstrated by a validation test set of 74 diverse and structurally complex compounds that were not included in the least-squares analysis. The correlation coefficient for the validation set is 0.96.