Greenhouse effects from fossil fuel combustion leading to increased co
ncentrations of primary and secondary greenhouse gases (e.g., CO2, ozo
ne, etc.) have received considerable attention. More recently, it has
been suggested that clouds, aerosols, and fogs can play opposing roles
in climate forcing by scattering or absorbing incoming solar radiatio
n as well as by absorbing long-wave radiation as it escapes into space
. The total effect on the radiation balance depends on the relative ma
gnitude of these opposing forces, which in turn will depend on the com
position of the aqueous phase. This work describes the measurement of
water-soluble infrared absorbers which can contribute to the long-wave
radiative forcing of clouds, fogs, and aerosols. Aqueous species whic
h have been characterized include sulfate, nitrate, formate, acetate,
oxalate, phenol, p-nitrophenol, ammonium, bicarbonate, formaldehyde, m
ethanol, and ethanol. Infrared absorption band positions and band stre
ngths have been determined, and their relative effects on radiative fo
rcing are discussed.