The optical properties and chemical composition of Po Valley fog water

The chemical composition and solar radiation absorption properties of fog water are important because of the effects these properties can have on the climate. Fog samples contain compounds that may absorb light, and this radiative forcing may be significant. The Po Valley, located between the Apennine and Alps mountain ranges in Italy, has a high occurrence of fog events, which can be up to 30% of the time in the winter season. Absorption spectra of fog water samples from San Pietro Capofiume, Italy were taken in a Liquid Waveguide Capillary Cell with a UV-visible spectrophotometer. Spectra were fitted and absorptions at different wavelengths were correlated to the organic carbon and organic nitrogen concentrations of the samples. Ion chromatography was also used to obtain the concentrations of several ions such as nitrite, nitrate, sulfate, acetate, ammonium, and various amines. A correlation was found between absorbance and organic carbon content, as well as between absorbance at less than 300 nm wavelengths and organic nitrogen content. Characteristic absorptivities at 365 nm were calculated from Beer's law with regard to the organic carbon content and revealed similar results to those calculated from Los Angeles fog water samples earlier this year. The absorption angstrom exponents of the samples imply that the likely source of the optically active species is from biomass burning, and this will later be confirmed by a tracer analysis. High organic nitrogen : organic carbon ratios in all samples suggest that compounds containing nitrogen have a large contribution to the light absorbing properties of fog water.