"Climate and Forecast (CF)" . . "Mass fraction is used in the construction mass_fraction_of_X_in_Y, where X is a material constituent of Y. It means the ratio of the mass of X to the mass of Y (including X). \"Mass_fraction_of_ammonium\" means that the mass is expressed as mass of NH4. \"Aerosol\" means the suspended liquid or solid particles in air (except cloud droplets). Aerosol takes up ambient water (a process known as hygroscopic growth) depending on the relative humidity and the composition of the aerosol. \"Dry aerosol\" means aerosol without water." . "mass fraction of ammonium dry aerosol in air" . . .