A European aerosol phenomenology – 6: scattering properties of atmospheric aerosol particles from 28 ACTRIS sites
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 (<i>σ</i><sub>sp</sub>) and hemispheric backscatter...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/7877/2018/acp-18-7877-2018.pdf |
| Summary: | 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 (<i>σ</i><sub>sp</sub>) and hemispheric backscattering
(<i>σ</i><sub>bsp</sub>) coefficients, scattering Ångström exponent
(SAE), backscatter fraction (BF) and asymmetry parameter (<i>g</i>). An increasing
gradient of <i>σ</i><sub>sp</sub> is observed when moving from remote
environments (arctic/mountain) to regional and to urban environments. At a
regional level in Europe, <i>σ</i><sub>sp</sub> 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 <i>g</i> 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 <i>σ</i><sub>sp</sub> 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 <i>σ</i><sub>sp</sub> 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 <i>g</i>
minima). At all sites, both SAE and <i>g</i> show a strong variation with aerosol
particle loading. The lowest values of <i>g</i> are always observed together with
low <i>σ</i><sub>sp</sub> values, indicating a larger contribution from
particles in the smaller accumulation mode. During periods of high
<i>σ</i><sub>sp</sub> values, the variation of <i>g</i> 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 <i>σ</i><sub>sp</sub> are observed at 5 out of the
13 stations included in the trend analyses. The total reductions of
<i>σ</i><sub>sp</sub> are consistent with those reported for PM<sub>2.5</sub>
and PM<sub>10</sub> mass concentrations over similar periods across Europe. |
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| ISSN: | 1680-7316 1680-7324 |