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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 6041-6072, 2017
http://www.atmos-chem-phys.net/17/6041/2017/
doi:10.5194/acp-17-6041-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
16 May 2017
Comparison of AOD, AAOD and column single scattering albedo from AERONET retrievals and in situ profiling measurements
Elisabeth Andrews1, John A. Ogren2, Stefan Kinne3, and Bjorn Samset4 1CIRES, University of Colorado, Boulder, CO 80309, USA
2NOAA/ESRL/GMD, Boulder, CO 80305, USA
3Max Planck Institute for Meteorology, 20146 Hamburg, Germany
4Center for International Climate and Environmental Research – Oslo (CICERO), 0349 Oslo, Norway
Abstract. Here we present new results comparing aerosol optical depth (AOD), aerosol absorption optical depth (AAOD) and column single scattering albedo (SSA) obtained from in situ vertical profile measurements with AERONET ground-based remote sensing from two rural, continental sites in the US. The profiles are closely matched in time (within ±3 h) and space (within 15 km) with the AERONET retrievals. We have used Level 1.5 inversion retrievals when there was a valid Level 2 almucantar retrieval in order to be able to compare AAOD and column SSA below AERONET's recommended loading constraint (AOD > 0.4 at 440 nm). While there is reasonable agreement for the AOD comparisons, the direct comparisons of in situ-derived to AERONET-retrieved AAOD (or SSA) reveal that AERONET retrievals yield higher aerosol absorption than obtained from the in situ profiles for the low aerosol optical depth conditions prevalent at the two study sites. However, it should be noted that the majority of SSA comparisons for AOD440 > 0.2 are, nonetheless, within the reported SSA uncertainty bounds. The observation that, relative to in situ measurements, AERONET inversions exhibit increased absorption potential at low AOD values is generally consistent with other published AERONET–in situ comparisons across a range of locations, atmospheric conditions and AOD values. This systematic difference in the comparisons suggests a bias in one or both of the methods, but we cannot assess whether the AERONET retrievals are biased towards high absorption or the in situ measurements are biased low. Based on the discrepancy between the AERONET and in situ values, we conclude that scaling modeled black carbon concentrations upwards to match AERONET retrievals of AAOD should be approached with caution as it may lead to aerosol absorption overestimates in regions of low AOD. Both AERONET retrievals and in situ measurements suggest there is a systematic relationship between SSA and aerosol amount (AOD or aerosol light scattering) – specifically that SSA decreases at lower aerosol loading. This implies that the fairly common assumption that AERONET SSA values retrieved at high-AOD conditions can be used to obtain AAOD at low-AOD conditions may not be valid.

Citation: Andrews, E., Ogren, J. A., Kinne, S., and Samset, B.: Comparison of AOD, AAOD and column single scattering albedo from AERONET retrievals and in situ profiling measurements, Atmos. Chem. Phys., 17, 6041-6072, doi:10.5194/acp-17-6041-2017, 2017.
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Short summary
We compare absorption aerosol optical depth (AAOD) and single scattering albedo (SSA) from AERONET retrievals with AAOD and SSA obtained from in situ vertical profiling flights over two rural sites in North America. The direct comparisons of in situ derived to AERONET-retrieved AAOD (or SSA) reveal that AERONET retrievals yield higher aerosol absorption than obtained from the in situ profiles. This has implications for models using AERONET to evaluate or scale their simulated absorption values.
We compare absorption aerosol optical depth (AAOD) and single scattering albedo (SSA) from...
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