In situ UV–VIS–NIR absorbing properties of atmospheric aerosol particles: Estimates of the imaginary refractive index and comparison with columnar values

In this work, a novel technique is used to estimate the aerosol complex index of refraction of in situ collected samples. Samples of atmospheric particulate matter were collected in El Arenosillo, southern Spain, on polycarbonate filters during summer 2004 as part of an aerosol characterization campaign. These samples were analyzed for the volumetric absorption coefficient in the 320–800 nm spectral region and an estimation of the effective imaginary refractive index was made. The values of the imaginary part of the complex refractive index ranged between 0.0009–0.0215 at 800 nm and 0.0015–0.0114 at 320 nm. Little dependence on the wavelength was observed. Several intense and long lasting desert outbreaks were registered during the campaign and the complex refractive index almost doubles its value during these dust events. Finally, we present a comparison of data obtained in situ with columnar data obtained from the AERONET network. A correlation factor of 0.64 was obtained between both data, which gives an idea of how accurately the in situ ground data represent the total column. ► We estimate the imaginary refractive index of atmospheric aerosol particles. ► Estimates take into consideration spectrally resolved data in the range 320–800 nm. ► Little dependence on the wavelength was observed. ► Comparison with column values is presented for dust event and non event days. ► The data presented can be used by those working with radiative forcing by aerosols.