Long-term variability of aerosol optical thickness in Eastern Europe over2001–2014 according to the measurements at the Moscow MSU MO AERONET sitewith additional cloud and NO2 correction

[摘要] The atmospheric aerosol properties were obtained within the framework of theAERONET program at the Moscow State University Meteorological Observatory(Moscow MSU MO) over the 2001–2014 period. The quality data control hasrevealed the necessity of additional cloud screening and NO₂correction. The application of additional cloud screening according tohourly visual cloud observations provides a decrease in monthly averageaerosol optical thickness (AOT) at 500 nm of up to 0.03 compared with thestandard data set. We also show that the additional NO₂ correction ofthe AERONET version 2 data is needed in large megalopolis, like Moscow, with12 million residents and NO_x emission rates of about 100 kt yr⁻¹. According to the developed method, we estimated monthly meanNO₂ content, which provides an additional decrease of 0.01 for AOT at340 nm, and of about 0.015 – for AOT at 380 and 440 nm. The ratios ofNO₂ optical thickness to AOT at 380 and 440 nm are about 5–6 % insummer and reach 15–20 % in winter when both factors have similar effectson UV irradiance. Seasonal cycle of AOT at 500 nm is characterized by anoticeable summer and spring maxima, and a minimum in winter conditions,changing from 0.08 in December and January up to 0.3 in August. Theapplication of the additional cloud screening removes a local AOT maximum inFebruary. Statistically significant negative trends in annual AOT for UV andmid-visible spectral range have been obtained both for average and 50 %quantile values. The pronounced negative changes were observed in mostmonths with the rate of about −1–5 % yr⁻¹ and could be attributed tothe negative trends in emissions (E) of different aerosol precursors ofabout 135 Gg yr⁻² in E_SOx, 54 Gg yr⁻² in E_NMVOC, andslight negative changes in NO_x over the European part of Russia. Nosignificant influence of natural factors on temporal AOT variations has beenrevealed.

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