Multiwavelength Photoacoustic Measurements of Light Absorption and Scattering by Wood Smoke

Quantification of light absorption by wood smoke is not simple due to absorption by poorly-characterized organic species. We report simultaneous measurements of aerosol optics for a wide range of biomass smoke using the photoacoustic method for absorption and reciprocal nephelometry for scattering at 405 nm and 870 nm. These first of a kind measurements were made using a single photoacoustic instrument operating concurrently at two wavelengths. Ångström coefficients for absorption were found to range from 1 to 3. The measurements show conclusively that light absorbing organic material is present in wood smoke. Spectral properties of this organic material, which preferentially absorbs light at lower wavelengths, indicate that casual use of the inverse wavelength dependence of aerosol light absorption in remote sensing and modeling applications can introduce errors as large as a factor of 6 in the UV and a factor of 2 at visible wavelengths. Traditional filter-based Aethalometer measurement comparisons will be presented along with measurements by a photoacoustic instrument operating at a wavelength of 532 nm.