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

Abstract

In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was 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 pre-whitening methods and with Sen's slope was used as the main trend analysis method. 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 coefficient 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 coefficient 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 the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % 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 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes. ; European Union (EU) 654109 ; ACTRIS PPP project 739530 ; IMPROVE ; Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air pollutants in Europe (EMEP) under UNECE ; Korea Meteorological Administration Research and Development Program "Development of Monitoring and Analysis Techniques for Atmospheric Composition in Korea" KMA2018-00522 ; "Arctic Monitoring and Assessment Programme" (AMAP) under EU action "Black Carbon in the Arctic" 80026 ; Norwegian Environment Agency ; Basic Science Research Program through the National Research Foundation of Korea 2017R1D1A1B06032548 ; European Union (EU) 262254 ; European Union's Horizon 2020 research and innovation programme under project ACTRIS-2 654109 ; European Union's Horizon 2020 research and innovation programme under project iCUPE 689443 ; Academy of Finland 307331 264242 268004 284536 287440 ; AEMET ; Swiss State Secretariat for Education, Research and Innovation, SERI 15.0159-1 ; Taiwan Environmental Protection Administration ; Ministry of Science and Technology ; European Union's Horizon 2020 research and innovation programme 654109 ; MINECO (Spanish Ministry of Economy, Industry and Competitiveness) ; FEDER fund under the PRISMA project CGL2012-39623-C02/00 ; FEDER fund under the HOUSE project CGL2016-78594-R ; Generalitat de Catalunya AGAUR 2014 SGR33 AGAUR 2017 SGR41 ; Business Finland 2634/31/2015 ; Ramon y Cajal Fellowship - Spanish Ministry of Economy and Competitiveness RYC-2013-14036 ; Department of Biotechnology (DBT) India 2634/31/2015 ; Academy of Finland 307331 ; National Oceanic Atmospheric Admin (NOAA) - USA ; ACTRIS-France National Research infrastructure ; CNRS-INSU long-term observing program ; Spanish Ministry of Economy and Competitiveness CGL2016-81092-R CGL2017-90884-REDT RTI2018-101154-A-I00 ; National Natural Science Foundation of China (NSFC) 41675129 ; National Key Project of the Ministry of Science and Technology of the People's Republic of China 2016YFC0203305 2016YFC0203306 ; Basic Research Project of the Chinese Academy of Meteorological of Sciences 2017Z011 ; Knut-and-AliceWallenberg Foundation within the ACAS project (Arctic Climate Across Scales) 2016.0024 ; CPR: Para La Naturaleza and the nature reserve of Cabezas de San Juan and the support of grants AGS 0936879 and EAR1331841.