Browsing by Autor "Nicolas Bukowiecki"

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A European aerosol phenomenology – 6: scattering properties of atmospheric aerosol particles from 28 ACTRIS sites
(Copernicus Publications, 2018) Marco Pandolfi; Lucas Alados‐Arboledas; Andrés Alástuey; Marcos Andrade; Christo Angelov; Begoña Artı́ñano; John Backman; Urs Baltensperger; Paolo Bonasoni; Nicolas Bukowiecki
Abstract. This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of σsp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, σsp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intra-annual variability. At mountain sites, higher σsp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher σsp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low σsp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high σsp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of σsp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of σsp are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.
A European aerosol phenomenology – 6: scattering properties of atmospheric aerosol particles from 28 ACTRIS sites
(European Organization for Nuclear Research, 2018) Marco Pandolfi; Lucas Alados‐Arboledas; Andrés Alástuey; Marcos Andrade; Christo Angelov; Begoña Artı́ñano; John Backman; Urs Baltensperger; Paolo Bonasoni; Nicolas Bukowiecki
This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (sp) and hemispheric backscattering (bsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of sp is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, sp also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intraannual variability. At mountain sites, higher sp and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher sp values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low sp values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high sp values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of sp are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of sp are consistent with those reported for PM2:5 and PM10 mass concentrations over similar periods across Europe.
A European aerosol phenomenology-6: Scattering properties of atmospheric aerosolparticles from 28 ACTRIS sites
(2017) Marco Pandolfi; Lucas Alados‐Arboledas; Andrés Alástuey; Marcos Andrade; Begoña Artı́ñano; John Backman; Urs Baltensperger; Paolo Bonasoni; Nicolas Bukowiecki; Martine Collaud Coen
Abstract. This paper presents the light scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, located mainly in Europe. The data include particle light scattering (σsp) and hemispheric backscattering (σbsp) coefficients, scattering Ångström exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). A large range of ssp was observed across the network. Low ssp values were on average measured in Nordic and Baltic countries and in Western Europe whereas the highest σsp were measured at regional sites in eastern and central Europe. In these regional areas the SAE was also high indicating the predominance of fine-mode particles. On average, the SAE was lower in the Nordic and Baltic, western and southern countries suggesting a lower fraction of fine-mode particle compared to central and eastern Europe. An increasing gradient of ssp was observed when moving from mountain to regional and to urban sites. Conversely, the mass-independent SAE and g parameters did not show the same gradient. At all sites, both SAE and g varied greatly with aerosol particle loading. The lowest values of g were always observed under low ssp indicating a larger contribution from particles in the smaller accumulation mode. Then, g steeply increased with increasing ssp indicating a progressive shift of the particle size distribution toward the larger end of the accumulation mode. Under periods of high particle mass concentrations, the variation of g was less pronounced whereas the SAE increased or decreased suggesting changes mostly in the coarse aerosol particles mode rather than in the fine mode. The station placement seemed to be the main parameter affecting the intra-annual variability. At mountain sites, higher σsp was measured in summer mainly because of the enhanced boundary layer influence. Conversely, less horizontal and vertical dispersion in winter led to higher σsp at all low altitude sites in central and eastern Europe compared to summer. On average, these sites also showed SAE maxima in summer (and correspondingly g minima). Large intra-annual variability of SAE and g was observed also at Nordic and Baltic countries due to seasonal-dependent transport of different air masses to these remote sites. Statistically significant decreasing trends of σsp were observed at 5 out of 13 stations included in trend analyses. The total reductions of ssp were consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.
Identification of topographic features influencing aerosol observations at high altitude stations
(Copernicus Publications, 2018) Martine Collaud Coen; Elisabeth Andrews; Diego Aliaga; Marcos Andrade; Hristo Angelov; Nicolas Bukowiecki; Marina Ealo; Paulo Fialho; H. Flentje; A. Gannet Hallar
Abstract. High altitude stations are often emphasized as free tropospheric measuring sites but they remain influenced by atmospheric boundary layer (ABL) air masses due to convective transport processes. The local and meso-scale topographical features around the station are involved in the convective boundary layer development and in the formation of thermally induced winds leading to ABL air lifting. The station altitude alone is not a sufficient parameter to characterize the ABL influence. In this study, a topography analysis is performed allowing calculation of a newly defined index called ABL-TopoIndex. The ABL-TopoIndex is constructed in order to correlate with the ABL influence at the high altitude stations and long-term aerosol time series are used to assess its validity. Topography data from the global digital elevation model GTopo30 were used to calculate five parameters for 43 high and 3 middle altitude stations situated on five continents. The geometric mean of these five parameters determines a topography based index called ABL-TopoIndex, which can be used to rank the high altitude stations as a function of the ABL influence. To construct the ABL-TopoIndex, we rely on the criteria that the ABL influence will be low if the station is one of the highest points in the mountainous massif, if there is a large altitude difference between the station and the valleys or high plains, if the slopes around the station are steep, and finally if the inverse drainage basin potentially reflecting the source area for thermally lifted pollutants to reach the site is small. All stations on volcanic islands exhibit a low ABL-TopoIndex, whereas stations in the Himalayas and the Tibetan Plateau have high ABL-TopoIndex values. Spearman's rank correlation between aerosol optical properties and number concentration from 28 stations and the ABL-TopoIndex, the altitude and the latitude are used to validate this topographical approach. Statistically significant (SS) correlations are found between the 5th and 50th percentiles of all aerosol parameters and the ABL-TopoIndex, whereas no SS correlation is found with the station altitude. The diurnal cycles of aerosol parameters seem to be best explained by the station latitude although a SS correlation is found between the amplitude of the diurnal cycles of the absorption coefficient and the ABL-TopoIndex.
The topography contribution to the influence of the atmospheric boundary layer at high altitude stations
(2017) Martine Collaud Coen; Elisabeth Andrews; Diego Aliaga; Marcos Andrade; Hristo Angelov; Nicolas Bukowiecki; Marina Ealo; Paulo Fialho; H. Flentje; A. Gannet Hallar
Abstract. High altitude stations are often emphasized as free tropospheric measuring sites but they remain influenced by atmospheric boundary layer (ABL) air masses due to convective transport processes. The local and meso-scale topographical features around the station are involved in the convective boundary layer development and in the formation of thermally induced winds leading to ABL air lifting. The station altitude is not a sufficient parameter to characterize the ABL influence. Topography data from the global digital elevation model GTopo30 were used to calculate 5 parameters for 46 high altitude stations situated in five continents. The geometric mean of these 5 parameters determines a topography based index called ABL-TopoIndex which can be used to rank the high altitude stations as a function of the ABL influence. To construct the ABL-TopoIndex, we rely on the criteria that the ABL influence will be low if the station is one of the highest points in the mountainous massif, if there is a large altitude difference between the station and the valleys or plateaus, if the slopes around the station are steep, and finally if the drainage basin for air convection is small. All stations on volcanic islands exhibit a low ABL-TopoIndex whereas stations in the Himalaya and the Tibetan Plateau have high ABL-TopoIndex values. Spearman's rank correlation between aerosol optical properties and number concentration from 28 stations and the ABL-TopoIndex, the altitude and the latitude are used to validate this topographical approach. Statistically significant (s.s.) correlations are found between the 5 and 50 percentiles of all aerosol parameters and the ABL-TopoIndex whereas no s.s. correlation is found with the station altitude. The diurnal cycles of aerosol parameters seem to be best explained by the station latitude although a s.s. correlation is found between the amplitude of the diurnal cycles of the absorption coefficient and the ABL-TopoIndex. Finally, the main flow paths for air convection were calculated for various ABL heights.