Long-term trends in reconstructed atmospheric aerosol load based on large-scale sunshine duration records since 1900

Abstract. This study uses multiple observational networks, utilizing sunshine duration as a proxy for broadband AOD (BAOD) from 2700 sites across the world, to reconstruct BAOD trends since the late 19th century. The findings include a general trend toward cleaner atmospheres at most European sites during both the 1900–1925 and 1926–1959 periods, amounting to regional trends of –0.014 decade^–1 and –0.004 decade^–1, respectively. Aerosol concentrations are found to increase at only a few stations, likely because of local industrialization. Conversely, during the 1960–1985 period, the analysis, underscores the role of anthropogenic aerosols in the dimming observed across Europe (0.004 decade^–1), as well as the modulating relevance of volcanic aerosols. A continuous increase in BAOD is also observed over Southeast Brazil during 1960–1985, with a noticeable higher rate of 0.015 decade^–1, which is approximately four times as large as that found in Europe. At the same time, Japan experienced a notable decrease in BAOD with a rate of –0.015 decade^–1, owing to stringent environmental regulations implemented between 1960 and 1985. Meanwhile, Oceania exhibited a modest negative trend of –0.004 decade^–1 during that period. During the 1986–2015 period, commonly referred to as “brightening phase”, a general decline of annual BAOD is observed in each studied region: higher rate of decreasing aerosol load in Southeast Brazil, Japan, and Europe by –0.010 decade^–1, –0.015 decade^–1, and –0.013 decade^–1, respectively, compared to much the lower rate of –0.003 decade^–1 over Oceania.