Multidecadal trend analysis of aerosol radiative properties at a global scale

Abstract

<p><strong>Abstract.</strong> In order to assess the global evolution of aerosol parameters affecting climate change, a long-term trend analyses of aerosol optical properties were performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several prewhitening methods and with the Sen's slope were used as main trend analysis methods. Comparisons with General Least Mean Square associated with Autoregressive Bootstrap (GLS/ARB) and with standard Least Mean Square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficients trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficients time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, Eastern/Northern Europe and Arctic, 18 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 30 % of sites have trends, which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10 year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10 year trends are primarily found for earlier periods (10 year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10 year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10 year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10 year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2010–2011 for all stations in the eastern and central US. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage enables a better global view of potential aerosol effects on climate changes.</p>

Asian Emissions Explain Much of the Arctic Black Carbon Events

“…Long term surface concentrations of BC in the Arctic have mostly decreased during the 1990s and 2000s (Hirdman, Burkhart, et al., 2010; Sharma et al., 2013). Recently, this trend seems to have leveled off with little to no trend observed for surface level BC in the Arctic during the last decade based on a trend analysis including all seasons (Coen et al., 2020). However, higher up in the Arctic atmosphere the situation might be different as East Asia is expected to contribute more substantially to the BC levels at higher altitudes (Ikeda et al., 2017; Sharma et al., 2013).…”

Multidecadal trend analysis of in situ aerosol radiative properties around the world

“…Almost all datasets are available as level 2 NASA/AMES files at EBAS (http://ebas.nilu.no/, last access: 20 July 2020) at an hourly resolution. The screened datasets used for this study aggregated as daily medians can be found at https://doi.org/10.21336/c4dy-yw57 (Collaud Coen et al, 2020b).…”

Dark Glacier Surface of Greenland’s Largest Floating Tongue Governed by High Local Deposition of Dust

“…For long term trends in BC, global emissions were estimated to grow by about 15% by 2010 compared to 1990 [50]. The aerosol light absorption levels do not show a significant trend in the Arctic as recently displayed in the analysis by Collaud Coen et al [22] for long term data from Arctic stations Alert, Summit and Zeppelin-Ny Ålesund.…”

“…Recently, a study has found 10 year long trends to exhibit no statistically significant change for several areas including Svalbard (Ny-Ålesund), Greenland (Summit) and a slight increasing trend at Alert [22]. Despite global BC may have increased from 1990 to 2010, Arctic BC decreased dramatically over that same time span [19,23,24].…”