Abstract
Abstract. The absorbing aerosol index (AAI) is a qualitative parameter directly calculated from satellite-measured reflectance. Its sensitivity to absorbing aerosols in combination with a long-term data record since 1978 makes it an important parameter for climate research. In this study, we attempt to quantify aerosol absorption by retrieving the single-scattering albedo (ω0) at 550 nm from the satellite-measured AAI. In the first part of this study, AAI sensitivity studies are presented exclusively for biomass-burning aerosols. Later on, we employ a radiative transfer model (DISAMAR) to simulate the AAI measured by the Ozone Monitoring Instrument (OMI) in order to derive ω0 at 550 nm. Inputs for the radiative transfer calculations include satellite measurement geometry and surface conditions from OMI, aerosol optical thickness (τ) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and aerosol microphysical parameters from the AErosol RObotic NETwork (AERONET), respectively. This approach is applied to the Chile wildfires for the period from 26 to 30 January 2017, when the OMI-observed AAI of this event reached its peak. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) overpasses missed the evolution of the smoke plume over the research region; therefore the aerosol profile is parameterized. The simulated plume is at an altitude of 4.5–4.9 km, which is in good agreement with available CALIOP backscatter coefficient measurements. The data may contain pixels outside the plume, so an outlier detection criterion is applied. The results show that the AAI simulated by DISAMAR is consistent with satellite observations. The correlation coefficients fall into the range between 0.85 and 0.95. The retrieved mean ω0 at 550 nm for the entire plume over the research period from 26 to 30 January 2017 varies from 0.81 to 0.87, whereas the nearest AERONET station reported ω0 between 0.89 and 0.92. The difference in geolocation between the AERONET site and the plume, the assumption of homogeneous plume properties, the lack of the aerosol profile information and the uncertainties in the inputs for radiative transfer calculation are primarily responsible for this discrepancy in ω0.
Highlights
Biomass-burning aerosols are generated from combustion of carbon-containing fuels, either by natural or anthropogenic processes (Bond et al, 2004; IPCC, 2014)
We employ the radiative transfer model DISAMAR to simulate the near-UV absorbing aerosol index (AAI) from Ozone Monitoring Instrument (OMI) and to derive the ω0 for a specific case, i.e. the Chile wildfires in January 2017
By applying the methodology described in the previous section, we quantitatively retrieved the aerosol layer height and ω0 at 550 nm of the Chile 2017 wildfires by AAI simulation
Summary
Biomass-burning aerosols are generated from combustion of carbon-containing fuels, either by natural or anthropogenic processes (Bond et al, 2004; IPCC, 2014). They are of great concern from the climate perspective (Kaufman et al, 2002; IPCC, 2007, 2014; Koch and Del Genio, 2010; Myhre et al, 2013). Ω0 is mainly measured by ground-based instruments (Dubovik et al, 1998; Eck et al, 2003; Petters et al, 2003; Kassianov et al, 2005; Corr et al, 2009; Yin et al, 2015). Satellite sensors, such as the POLarization and Directionality of the Earth’s Reflectance (POLDER), can retrieve ω0 from a combination of multi-angular, multispectral observations of the Published by Copernicus Publications on behalf of the European Geosciences Union
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