Abstract
Abstract. This study presents an inter-comparison of two active remote sensors (lidar and ceilometer) to determine the mixing layer height and structure of the Planetary Boundary Layer (PBL) and to retrieve tropospheric aerosol vertical profiles over Athens, Greece. This inter-comparison was performed under various strongly different aerosol loads/types (urban air pollution, biomass burning and Saharan dust event), implementing two different lidar systems (one portable Raymetrics S.A. lidar system running at 355 nm and one multi-wavelength Raman lidar system running at 355 nm, 532 nm and 1064 nm) and one CL31 Vaisala S.A. ceilometer (running at 910 nm). Spectral conversions of the ceilometer's data were performed using the Ångström exponent estimated by ultraviolet multi-filter radiometer (UV-MFR) measurements. The inter-comparison was based on two parameters: the mixing layer height determined by the presence of the suspended aerosols and the attenuated backscatter coefficient. Additionally, radiosonde data were used to derive the PBL height. In general, a good agreement was found between the ceilometer and the lidar techniques in both inter-compared parameters in the height range from 500 m to 5000 m, while the limitations of each instrument are also examined.
Highlights
The dynamics of the Planetary Boundary Layer (PBL) are directly influenced by the Earth’s surface, solar irradiance and anthropogenic activities
The choice of the reference height for the Klett aerosol backscatter coefficient at wavelength λ retrievals in the case of the lidar signals was set at 7 km, since the signal to noise ratio (SNR) is still quite high even during daytime (higher than 1, according to our SNR calculations based on Heese et al (2010), for averaging time over more than 30 min)
The corresponding lidar measurements (Fig. 2b and c) showed that the PBL height ranged from 700 m to 1500 m, which is a typical evolution of the PBL due to increased solar irradiance (Stull, 1998)
Summary
The dynamics of the Planetary Boundary Layer (PBL) are directly influenced by the Earth’s surface, solar irradiance and anthropogenic activities. The influences of anthropogenic activities and earth’s surface upon air quality can be monitored by studying the aerosol concentration and their relevant optical, microphysical and chemical properties (Seinfeld and Pandis, 2006) Laser remote sensors, such as lidars and ceilometers, are proven to be powerful tools for tracking and monitoring the evolution of the PBL height (Papayannis and Balis, 1998; Amiridis et al, 2007), as well as the vertical profiles of aerosol properties over long time periods (Amiridis et al, 2005). Heese et al (2010) compared aerosol backscatter coefficient profiles retrieved by a new generation CHM15K-X Jenoptik ceilometer and the IfT’s lidar Polly in Leipzig (Germany) and suggested that the ceilometer is able to detect aerosol layers in the PBL and in the free troposphere up to altitudes of the order of 4 km during day time, while during nighttime, this altitude may extend higher, depending on the aerosol load present.
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