Publikationsdatum:
2019-12-03
Beschreibung:
Currently many ground-based atmospheric stations
include in-situ measurements of aerosol physical and
optical properties, resulting in more than 20 long-term
(〉10 yr) aerosol measurement sites in the Northern Hemisphere
and Antarctica. Most of these sites are located at remote
locations and monitor the aerosol particle number concentration,
wavelength-dependent light scattering, backscattering,
and absorption coefficients. The existence of these
multi-year datasets enables the analysis of long-term trends
of these aerosol parameters, and of the derived light scattering
A° ngstro¨m exponent and backscatter fraction. Since the
aerosol variables are not normally distributed, three different
methods (the seasonal Mann-Kendall test associated with the
Sen’s slope, the generalized least squares fit associated with
an autoregressive bootstrap algorithm for confidence intervals,
and the least-mean square fit applied to logarithms of
the data) were applied to detect the long-term trends and their
magnitudes. To allow a comparison among measurement
sites, trends on the most recent 10 and 15 yr periods were calculated.
No significant trends were found for the three continental
European sites. Statistically significant trends were
found for the two European marine sites but the signs of the
trends varied with aerosol property and location. Statistically
significant decreasing trends for both scattering and absorption
coefficients (mean slope of −2.0%yr−1) were found for
most North American stations, although positive trends were
found for a few desert and high-altitude sites. The difference
in the timing of emission reduction policy for the Europe
and US continents is a likely explanation for the decreasing
trends in aerosol optical parameters found for most American
sites compared to the lack of trends observed in Europe. No
significant trends in scattering coefficient were found for the
Arctic or Antarctic stations, whereas the Arctic station had
a negative trend in absorption coefficient. The high altitude
Pacific island station of Mauna Loa presents positive trends
for both scattering and absorption coefficients.
Repository-Name:
EPIC Alfred Wegener Institut
Materialart:
Article
,
isiRev
Format:
application/pdf
Permalink