This is a Major Research Instrumentation award to support the development of an instrument for measuring the absorption of aerosol particles at different wavelengths in the solar spectrum. Aerosols absorb and scatter solar radiation and thus influence regional and global climate. Though accurate data on aerosol absorption spectra are lacking, the available evidence indicates that aerosols from different sources have markedly different spectra. For example, Saharan dust appears to absorb strongly in the ultraviolet but weakly in the visible part of the spectrum. Diesel soot, on the other hand, absorbs more uniformly over the spectrum. To now, no instrument has been available to measure the in-situ absorption of aerosols at more than two wavelengths, though what is needed for radiative transfer calculations is a detailed representation of the absorption spectrum. Accordingly, a multi-wavelength unit will be built, based on the resonant photoacoustic principle, to measure the absorption at six wavelengths spanning the spectrum from the ultraviolet to the infrared. Calibration is established by measuring the (known) absorption of the 760-nm oxygen A-band. The instrument will be employed for measurements of the spectral absorption of different kinds of natural and anthropogenic aerosols. This information is essential for understanding the consequences of the human use of combustion on climate.
