Composition of Aerosol Particles in a Desert Environment Using an Aerosol Raman Hyperspectral Imager

Aerosol particles (mineral, black carbon, and organic) can impact climate and visibility both by directly absorbing and scattering light, and by serving as cloud- and ice-condensation nuclei. The impacts to climate and visibility depend on the composition, which in turn can depend on emission, transport, and transformation of aerosol particles. Raman microspectroscopy can be used to examine the composition of some kinds of aerosol particles, including mineral dusts. Typically, particles are analyzed with longer time-resolution in an offline manner. To increase the number of particles that can be analyzed using Raman spectroscopy, Battelle (Columbus, OH) developed an aerosol Raman hyperspectral imager (ARHI) which it terms the REBS. We used this ARHI on the Jornada Experimental Range (NM, USA) to collect particles onto a metalized tape and measure hyperspectral Raman images with 15- or 20- minute time resolution. A total of 6306 Raman spectra (RS) were above the thresholds over the 48-hour measurement period. A single spectrum is not indicative of a single particle, multiple spectra could originate from the same particle. Of the above-threshold Raman spectra, 2567 exhibited broad luminescence, 2647 contained the D and G peaks (associated with, e.g., black carbon), 130 were consistent with quartz and 102 were consistent with calcite or dolomite. We discuss changes in measured particle compositions (20-minute time resolution) during a convective dust event: an order of magnitude higher levels of luminescence spectra (compared to the median) were observed, relatively high levels of quartz and calcite were observed, but the number of spectra with the D and G peaks were within the interquartile range for the measurement period.