Abstract
The impact of absorbing aerosols on climate is complex, with their potential positive or negative forcing, depending on many factors, including their height distribution and reflective properties of the underlying background. Measurement data is very limited, due to insufficient remote sensing methods dedicated to the retrieval of their vertical distribution. Columnar values of absorbing aerosol optical depth (AAOD) and single scattering albedo (SSA) are retrieved by the Aerosol Robotic Network (AERONET). However, the number of available results is low due to sky condition and aerosol optical depth (AOD) limitation. Presented research describes results of field campaigns in Strzyżów (South-East Poland, Eastern Europe) dedicated to the comparison of the absorption coefficient and SSA measurements performed with on-ground in-situ devices (aethalomter, nephelometer), small unmanned aerial system (UAS) carrying micro-aethalometer, as well as with lidar/ceilometer. An important aspect is the comparison of measurement results with those delivered by AERONET. Correlation of absorption to scattering coefficients measured on ground (0.79) and correlation of extinction on ground to AOD measured by AERONET (0.77) was visibly higher than correlation between AOD and AAOD retrieved by AERONET (0.56). Columnar SSA was weakly correlated with ground SSA (higher values of columnar SSA), which were mainly explained by hygroscopic effects, increasing scattering coefficient in ambient (wet conditions), and partly high uncertainty of SSA retrieval. AAOD derived with the use of profiles from UAS up to PBL height, was estimated to contribute in average to 37% of the total AAOD. A method of AAOD estimation, in the whole troposphere, with use of measured vertical profiles of absorption coefficient and extinction coefficient profiles from lidars was proposed. AAOD measured with this method has poor correlation with AERONET data, however for some measurements, within PBL, AAOD was higher than reported by AERONET, suggesting potential underestimation in photometric measurement under particular conditions. Correlation of absorption coefficient in profile to on ground measurements decrease with altitude. Measurements of SSA from drones agree well with ground measurements and are lower than results from AERONET, which suggests a larger contribution of absorbing aerosols. As an alternative for AAOD estimation in case of lack of AERONET AAOD data simple models are proposed, which base on AOD scaling with SSA measured with different methods. Proposed solution increase potential of absorption coefficient measurements in vertical profiles and columns of the atmosphere. Presented solutions make measurements of absorption coefficients in vertical profiles more affordable and allow rough estimation of columnar values for the whole atmosphere.
Highlights
The climate impact of absorbing aerosols, such as organic and black carbon (BC) particles originating from fossil fuel combustion or biomass burning, mineral dust and volcanic ash, is still poorly known [1]
Aerosol Robotic Network (AERONET) or the opposite, where absorbing aerosol optical depth (AAOD) was measured by AERONET, but there are no data from atmosphere sounding
We found moderate correlation between AERONET aerosol optical depth (AOD) and AAOD
Summary
The climate impact of absorbing aerosols, such as organic and black carbon (BC) particles originating from fossil fuel combustion or biomass burning, mineral dust and volcanic ash, is still poorly known [1]. It is due to several reasons, mainly too few observations of absorbing aerosol, large uncertainties in direct measurements and too simplified description of physical processes involving absorbing aerosols used for climate modelling [1,2]. In the case of absorbing aerosol amount of absorbing particles and vertical profiles are important for climate processes [5,7]. The simulations performed by climate models, which include only an idealised absorbing aerosol scheme, show that the average surface temperature is a function of the altitude at which the layer of the absorbing particles exists [6]. Taking into account that optical properties of absorbing particles could vary along the vertical profile, it could significantly influence the assessment of the direct aerosol effect [9,10,11]
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