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.