17 January 2023
The aerosol optical properties (AOP) VAP combines data from two instruments, a filter-based light absorption instrument (Particle Soot Absorption Photometer (PSAP), Tricolor Absorption Photometer (TAP), or Continuous Light Absorption Photometer (CLAP)), and scattering from a nephelometer, and calculates several intensive and extensive aerosol optical properties at three wavelengths. Calibrations and corrections are applied to both the scattering and absorption data to yield a consistent data product with uniform application of literature corrections. Notable reported extensive aerosol optical properties include corrected scattering, absorption, and absorption coefficients. Intensive aerosol optical properties include single scattering albedo, backscatter fraction, asymmetry parameter, and angstrom exponents for scattering and absorption. Data are available at time resolution of 1 minute or 1 hour.
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The AOP VAP contains, in a single file, most relevant intensive and extensive aerosol optical properties measures from in-situ instruments. These measurements are used to understand how aerosol particles absorb and scatter light and ultimately to understand radiative forcing. Some of the optical absorption measurements may also be used to infer the quantity of black carbon in the atmosphere. Scattering measurement can be used to derive aerosol mass loadings and in some cases and with additional assumptions, an aerosol size distribution.
All absorption measurements used in this VAP are derived from filter-based instruments. While filter-based measurements are very sensitive, there are inherent artifacts in the data that are similar in magnitude to typical aerosol absorption signals. Therefore, the absolute absorption measurements and quantities derived from them (e.g. SSA) should be used with caution when aerosol loading is low. Please see the technical report for more information.