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. ; The authors would like to thank the numerous, but unfortunately unnamed, technical and scientific staff members of the stations as well as many students included in these analyses, whose dedication to quality for decades have made this paper possible. Provision of data from this study has mainly been acquired in the framework of NOAA-FAN (https://www.esrl.noaa.gov/gmd/aero/net/); ACTRIS, under the ACTRIS-2 (Aerosols, Clouds, and Trace gases Research InfraStructure) project supported by European Union (grant agreement no. 654109) and the ACTRIS PPP project under grant agreement no. 739530; and IMPROVE (http://vista.cira.colostate.edu/Improve/). Some European sites and measurements were also supported by the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air pollutants in Europe (EMEP) under UNECE. The authors are also grateful to the following persons and organizations. AMY: the Korea Meteorological Administration Research and Development Program "Development of Monitoring and Analysis Techniques for Atmospheric Composition in Korea" under grant KMA2018-00522 APP: Appalachian State College of Arts and Sciences, electronics technician Michael Hughes, machinist Dana Greene BEO: ACTRIS-BG project BIR: project no. 80026 "Arctic Monitoring and Assessment Programme" (AMAP) under EU action "Black Carbon in the Arctic". Aerosol optical/physical properties at Birkenes II are financed by the Norwegian Environment Agency CGO: the Australian Bureau of Meteorology and all the staff from the Bureau of Meteorology and CSIRO, particularly John Gras who instigated the measurements of aerosol scattering and absorption CPR: Para La Naturaleza and the nature reserve of Cabezas de San Juan and the support of grants AGS 0936879 and EAR-1331841. GSN: the Basic Science Research Program through the National Research Foundation of Korea (2017R1D1A1B06032548). SMR: the European Union Seventh Framework Programme under grant agreement no. 262254, the European Union's Horizon 2020 research and innovation programme under grant agreement no. 654109 via project ACTRIS-2 and grant agreement no. 689443 via project iCUPE, the Academy of Finland (project no. 307331). IMPROVE: IMPROVE is a collaborative association of state, tribal, and federal agencies, and international partners. Support for IMPROVE nephelometers comes from the National Park Service. The assumptions, findings, conclusions, judgments, and views presented herein are those of the authors and should not be interpreted as necessarily representing the National Park Service (stations: ACA, BBE, CRG, GBN, GLR, GSM, HGC, MCN, MRN, MZW, NCC, RMN, SCN, SHN). IZO: Measurement Programme within the Global Atmospheric Watch (GAW) Programme at the Izaña Atmospheric Research Centre, financed by AEMET. JFJ: Urs Baltensperger, Günther Wehrle, Erik Herrmann; the International Foundation High Altitude Research Station Jungfraujoch and Gornergrat (HSFJG), the Swiss contributions (GAW-CH and GAW-CH-Plus) to the Global Atmosphere Watch programme of the World Meteorological Organization (WMO) which are coordinated by MeteoSwiss; the Swiss State Secretariat for Education, Research and Innovation, SERI, under contract number 15.0159-1 (ACTRIS-2 project). The opinions expressed and arguments employed herein do not necessarily reflect the official views of the Swiss Government. LLN: the Taiwan Environmental Protection Administration and the Ministry of Science and Technology for the support to individual PI's research funding. MSY: the European Union's Horizon 2020 research and innovation programme under grant agreement no. 654109, MINECO (Spanish Ministry of Economy, Industry and Competitiveness) and FEDER funds under the PRISMA project (CGL2012-39623-C02/00) and under the HOUSE project (CGL2016-78594-R), the MAGRAMA (Spanish Ministry of Agriculture, Food and Environment) and the Generalitat de Catalunya (AGAUR 2014 SGR33, AGAUR 2017 SGR41 and the DGQA). Marco Pandolfi is funded by a Ramón y Cajal Fellowship (RYC-2013-14036) awarded by the Spanish Ministry of Economy and Competitiveness. MUK: the Ministry of Foreign Affairs of Finland, project grants (264242, 268004, 284536, and 287440) received from Academy of Finland; Business Finland and DBT, India sponsored project (2634/31/2015), the Centre of Excellence in Atmospheric Science funded by the Finnish Academy of Sciences (307331), and an esteemed collaboration of FMI and TERI. NOAA stations (BND, BRW, MLO, SGP, SPO, SUM, THD): Derek Hageman for all his programming efforts for NOAA and NFAN stations, John Ogren for initiating the expanded NFAN measurements and NOAA's Climate Program Office for funding PAY: the Swiss Federal Office for the Environment (FOEN). PUY: the staff of OPGC and LaMP, INSU-CNRS and the University Clermont Auvergne, and the financial support from ACTRIS-France National Research infrastructure and CNRS-INSU long-term observing program. SGP: the U.S. Department of Energy Atmospheric Radiation Measurement Program via Argonne National Laboratory, the DOE SGP ARM Climate Research Facility staff and scientists. TIK: the Aethalometer was supplied by Russ Schnell; Tiksi overall logistics and operations by Taneil Uttal and Sara Morris (NOAA/ESRL/PSD, Boulder, CO, USA). UGR: the Spanish Ministry of Economy and Competitiveness through projects CGL2016-81092-R, CGL2017-90884-REDT and RTI2018-101154-A-I00. WLG: China Meteorological Administration, National Scientific Foundation of China (41675129), National Key Project of the Ministry of Science and Technology of the People's Republic of China (2016YFC0203305 and 2016YFC0203306), and Basic Research Project of the Chinese Academy of Meteorological of Sciences (2017Z011) and the Innovation Team for Haze-fog Observation and Forecasts of China Meteorological Administration. ZEP: the Swedish EPA's (Naturvårdsverket) Environmental monitoring program (Miljöövervakning), the Knut-and-Alice-Wallenberg Foundation within the ACAS project (Arctic Climate Across Scales, project no. 2016.0024), the research engineers Tabea Henning, Ondrej Tesar and Birgitta Noone from ACES and the staff from the Norwegian Polar Institute (NPI), NPI for substantial long-term support in maintaining the measurements, Maria Burgos and Dominic Heslin-Rees (ACES) for preparing the data.