Abstract
During August 2016, a quasi-stationary high-pressure system spreading over Central and North-Eastern Europe, caused weather conditions that allowed for 24/7 observations of aerosol optical properties by using a complex multi-wavelength PollyXT lidar system with Raman, polarization and water vapour capabilities, based at the European Aerosol Research Lidar Network (EARLINET network) urban site in Warsaw, Poland. During 24–30 August 2016, the lidar-derived products (boundary layer height, aerosol optical depth, Ångström exponent, lidar ratio, depolarization ratio) were analysed in terms of air mass transport (HYSPLIT model), aerosol load (CAMS data) and type (NAAPS model) and confronted with active and passive remote sensing at the ground level (PolandAOD, AERONET, WIOS-AQ networks) and aboard satellites (SEVIRI, MODIS, CATS sensors). Optical properties for less than a day-old fresh biomass burning aerosol, advected into Warsaw’s boundary layer from over Ukraine, were compared with the properties of long-range transported 3–5 day-old aged biomass burning aerosol detected in the free troposphere over Warsaw. Analyses of temporal changes of aerosol properties within the boundary layer, revealed an increase of aerosol optical depth and Ångström exponent accompanied by an increase of surface PM10 and PM2.5. Intrusions of advected biomass burning particles into the urban boundary layer seem to affect not only the optical properties observed but also the top height of the boundary layer, by moderating its increase.
Highlights
The fair-weather, being a prerequisite for remote sensing observations of aerosol optical properties, leads to a clear-sky observational bias, which is obvious in the measurements of the EARLINET [1] and AERONET [2] networks
Active remote sensing measurements were performed at three sites of the Poland aerosol optical depth (AOD) network in already-introduced Warsaw and Strzyzow, as well as in Raciborz located in the vicinity of the coal industry region of Silesia (Western Carpathians, south-western Poland)
For the case discussed here, the gradual increase of both the aerosol load and the boundary layer top certainly was related to large-scale displacement of the high-pressure system, this could not have been dominating cause, as it did not manifest at the two other sites in Strzyzow and Raciborz
Summary
The fair-weather, being a prerequisite for remote sensing observations of aerosol optical properties, leads to a clear-sky observational bias, which is obvious in the measurements of the EARLINET [1] and AERONET [2] networks. Over Europe, the cloudless conditions are often related to persistent for several days, quasi-stationary high pressure systems covering large geographical areas of the continent Such weather dynamics provide an excellent test-bed for performing quasi-continuous ground-based passive and/or active remote sensing of optical properties of aerosols suspended in the air above the measurement site, whether on a local [3,4,5] or regional scale [6,7]. The altitude of the boundary layer top, as well as vertical change of wind speed and temperature significantly impact vertical distribution of the aerosol optical and microphysical properties in the lower troposphere [11,12,13,14] They are found to have an effect on concentrations of air pollutants, over large cities [5,15,16]. Anti-correlations of boundary layer height and surface PM2.5 with the Ångström exponent are discernible for highly polluted urban atmosphere [5]
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