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

摘要

We introduce a new instrument for the measurement of in situ ambient aerosolextinction over the 300–700 nm wavelength range, the spectral aerosolextinction (SpEx) instrument. This measurement capability is envisioned tocomplement existing in situ instrumentation, allowing for simultaneousmeasurement of the evolution of aerosol optical, chemical, and physicalcharacteristics in the ambient environment. In this work, a detaileddescription of the instrument is provided along with characterization testsperformed in the laboratory. Measured spectra of NO and polystyrenelatex spheres (PSLs) agreed well with theoretical calculations. Goodagreement was also found with simultaneous aerosol extinction measurements at450, 530, and 630 nm using CAPS PMex instruments in a series of 22 testsincluding nonabsorbing compounds, dusts, soot, and black and brown carbonanalogs. SpEx measurements are expected to help identify the presence ofambient brown carbon due to its 300 nm lower wavelength limit compared tomeasurements limited to longer UV and visible wavelengths. Extinction spectraobtained with SpEx contain more information than can be conveyed by a simplepower law fit (typically represented by Ångström exponents). Plannedfuture improvements aim to lower detection limits and ruggedize theinstrument for mobile operation.