Raman spectra of atmospheric particles measured in Maryland, USA over 22.5 h using an automated aerosol Raman spectrometer

Raman spectroscopy can be used to determine the vibrational frequencies of materials and from these the chemical compositions. Raman microspectroscopy (RMS) can help in understanding the chemistry of atmospheric and other aerosols. This paper describes the use of an automated Aerosol Raman Spectrometer (ARS) from Battelle to collect approximately 100,000 RS in 15-min intervals over 22.5 h in Maryland, USA. Approximately 9000 of these RS have intensities exceeding the thresholds used in this analysis. This paper describes and illustrates processing techniques used for the RS, including detection and removal of RS exhibiting charring, and estimation and removal of fluorescence and other broad features. RS exhibiting the D and G bands of soots and other black carbons (labeled DG Carbon or DGC), are especially common in the data, probably because the particles are charged to increase the collection efficiency of small particles; the Raman cross sections of DGC are large; and the sampling location is near major roads. RS consistent with calcium oxalate hydrates (C2O4)Ca (1 + x)H2O where x = 0 (whewellite) and x = 1 (weddellite) are observed. RS with the nu((C-O)) frequency intermediate between the x = 0 and 1 extremes are also observed, possibly suggesting calcium oxalates with x between 0 and 1, or mixed oxalates including other metals, e.g., Fe or Mg. Other materials consistent with the measured RS are calcite, dolomite, gypsum, anhydrite, quartz, orthoclase, jadeite or muscovite, biological materials, and iron oxides. The measured RS data set and code to process these are provided. Published by Elsevier Ltd.