Articles | Volume 8, issue 11
Research article
11 Nov 2015
Research article |  | 11 Nov 2015

Spectral aerosol extinction (SpEx): a new instrument for in situ ambient aerosol extinction measurements across the UV/visible wavelength range

C. E. Jordan, B. E. Anderson, A. J. Beyersdorf, C. A. Corr, J. E. Dibb, M. E. Greenslade, R. F. Martin, R. H. Moore, E. Scheuer, M. A. Shook, K. L. Thornhill, D. Troop, E. L. Winstead, and L. D. Ziemba

Abstract. We introduce a new instrument for the measurement of in situ ambient aerosol extinction over the 300–700 nm wavelength range, the spectral aerosol extinction (SpEx) instrument. This measurement capability is envisioned to complement existing in situ instrumentation, allowing for simultaneous measurement of the evolution of aerosol optical, chemical, and physical characteristics in the ambient environment. In this work, a detailed description of the instrument is provided along with characterization tests performed in the laboratory. Measured spectra of NO2 and polystyrene latex spheres (PSLs) agreed well with theoretical calculations. Good agreement was also found with simultaneous aerosol extinction measurements at 450, 530, and 630 nm using CAPS PMex instruments in a series of 22 tests including nonabsorbing compounds, dusts, soot, and black and brown carbon analogs. SpEx measurements are expected to help identify the presence of ambient brown carbon due to its 300 nm lower wavelength limit compared to measurements limited to longer UV and visible wavelengths. Extinction spectra obtained with SpEx contain more information than can be conveyed by a simple power law fit (typically represented by Ångström exponents). Planned future improvements aim to lower detection limits and ruggedize the instrument for mobile operation.

Short summary
We describe a new instrument developed to observe ambient atmospheric aerosol extinction spectra from 300 to 700nm. Laboratory tests were performed to demonstrate that the instrument compares well with theoretical calculations over that spectral range, as well as with commercially available instrumentation measuring aerosol extinction at three visible wavelengths. The unique spectral data will be used to explore linkages between ambient aerosol optical properties, chemistry, and microphysics.