Abstract
Abstract. In this study, we report on the retrieval of aerosol extinction profiles from ground-based scattered sunlight multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, carried out at Athens, Greece. It is the first time that aerosol profiles are retrieved from MAX-DOAS measurements in Athens. The reported aerosol vertical distributions at 477 nm are derived from the oxygen dimer (O4) differential-slant-column-density observations at different elevation angles by applying the BRemen Optimal estimation REtrieval for Aerosol and trace gaseS (BOREAS) retrieval algorithm. Four case studies have been selected for validation purposes; the retrieved aerosol profiles and the corresponding aerosol optical depths (AODs) from the MAX-DOAS are compared with lidar extinction profiles and with sun-photometric measurements (Aerosol Robotic Network, AERONET, observations), respectively. Despite the different approach of each method regarding the retrieval of the aerosol information, the comparison with the lidar measurements at 532 nm reveals a very good agreement in terms of vertical distribution, with r>0.90 in all cases. The AODs from the MAX-DOAS and the sun photometer (the latter at 500 nm) show a satisfactory correlation (with 0.45 < r < 0.7 in three out of the four cases). The comparison indicates that the MAX-DOAS systematically underestimates the AOD in the cases of large particles (small Ångström exponent) and for measurements at small relative azimuthal angles between the viewing direction and the sun. Better agreement is achieved in the morning, at large relative azimuthal angles. Overall, the aerosol profiles retrieved from MAX-DOAS measurements are of good quality; thus, new perspectives are opened up for assessing urban aerosol pollution on a long-term basis in Athens from continuous and uninterrupted MAX-DOAS measurements.
Highlights
Tropospheric aerosols originate from both natural and anthropogenic sources
An assessment of the retrieval of aerosol extinction profiles and aerosol optical depths (AODs) from MAX-DOAS measurements is presented for the first time for the urban environment of Athens
The profiling results are compared to lidar extinction profiles and to AODs obtained from sun-photometric measurements
Summary
Tropospheric aerosols originate from both natural and anthropogenic sources. The lifetime of aerosols in the troposphere ranges from a few days to a few weeks, depending on their size and meteorology M. Gratsea et al.: Retrieval and evaluation of aerosol profiles using MAX-DOAS measurements take part in atmospheric processes through (i) nucleation and interaction with clouds (e.g. Twomey et al, 1977; Rosenfeld et al, 2014); (ii) participation in chemical and photochemical reactions by providing the required surface for heterogeneous reactions to take place (Andreae and Crutzen, 1997); and (iii) absorption and scattering of incoming solar and earth’s IR radiation, affecting atmospheric dynamics and stability Significant decrease in UV–vis irradiance reaching the ground due to urban aerosol pollution has been reported in various cases Significant decrease in UV–vis irradiance reaching the ground due to urban aerosol pollution has been reported in various cases (e.g. Zerefos et al, 2009; Chubarova et al, 2011)
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