Analysis of Long-Term Measurements of Tropospheric Ozone at the St. Petersburg State University Observational Site in Peterhof

Tropospheric ozone (TO) is one of the major greenhouse gases and a toxic air pollutant. It plays a key role in various chemical and photochemical processes in the troposphere. Ozone concentrations, both at the surface level and in the free troposphere, are measured by various local and remote-sensing methods. The St. Petersburg State University observational site in Peterhof (NDACC site St. Petersburg) is equipped with a Bruker IFS 125HR Fourier spectrometer used for TO measurements and the Thermo Scientific Model 49i gas analyzer for monitoring surface ozone concentrations (SOCs). The temporal variability of TO in the 0–8 km layer for the period from April 2009 to October 2022 and of SOCs for the period from 2013 to 2021 has been analyzed. The seasonal cycle of TO and SOCs is similar to that of total ozone columns, but it is shifted in time by about 1 and 1.5 months, respectively. The maximal variation of TO from the average value for the period falls on the first half of April ~+16%; a minimum of about –(12–14)% is observed from mid-October to the end of December. In the middle of summer, there is also a slight increase in the TO variation at the level of +(7–8)%. A statistically significant decrease in the TO content by 0.34 ± 0.22% per year was also obtained. A comparison of hourly averaged data on TO with synchronized data of SOC measurements revealed an increase in the correlation coefficient (CC) (up to 0.5 or more) between the two values 3–4 h after local noon in the warm season, accompanied by an increase in SOCs. The increase in correlations is in good agreement with the increase in the height of the planetary boundary layer.