| Description: | The MAOS Aethalometer converts measured optical attenuation due to aerosols deposited onto
a filter at 7-wavelengths (880 nm, 700 nm, 565 nm, 520 nm, 470 nm, 430 nm, 370 nm) to a
black carbon (BC) mass\ concentration (ng/m3). The utility of this multi-wavelength
instrument is that it can readily distinguish the presence of black carbon (BC) from brown
carbon (BrC) by taking advantage of the differing absorption Angstrom exponents for black
carbon (α ≈1) and brown carbon (α ≈ 2 4). However, the end user is
reminded that when reporting BC concentration to use that value reported at 880 nm since
only BC absorbs at this wavelength. It is also to be noted BC mass concentrations
reported at other wavelengths (most notably in the near UV where BrC absorbs) are for
qualitative convenience in that the reported concentration does not mean that there is X ng/m3 of
any organic species. For example, if the reported concentration at 370 nm is 2000 ng/m3
and 1500 ng/m3 at 880 nm, the difference (500 ng/m3) is not how much organic species is
present. It simply means that additional optical absorption is present that is of the same
magnitude as if it were produced by the presence of 500 ng/m3 of BC. The seven-
wavelength Aethalometer is particularly well-suited for identifying biomass burning events. |