Variability in total contents based on long term stratospheric trends are measured by researchers at the A.M. Obukhov Institute of Atmospheric Physics. They are measuring levels of O₃ and NO₂ at the Kislovodsk High-Altitude Scientific Station (KHASS) and Zvenigorod Scientific Station (ZSS). This includes direct and zenith scattered UV solar radiation during mornings and evening twilight hours for NO₂.

The variability of data is analysed using the multivariate linear regression method and they can produce annual and seasonal estimates of trends for O₃ and NO₂. They have found a negative trend of NO₂ in total contents at both stations during winter-spring seasons, with KHASS station showing stronger negative trend. O3 also has a negative trend, appearing to change from positive to negative around the early 2000s at KHASS station.

Gruzdev, A.N., Arabov, A.Y., Elokhov, A.S. et al. Long-Term Observations of Stratospheric Species at the A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences: Analysis of Trends and Interannual Variations in the Total Contents of O3 and NO2. Izv. Atmos. Ocean. Phys. 58, 270–283 (2022). https://doi.org/10.1134/S0001433822030069