Near-surface ozone variability in the Karadag nature reserve

The work presents the results of a study of a near-surface ozone concentration variability in the Crimea at the background environmental monitoring station in the Karadag Nature Reserve (44°55 north latitude, 35°14 east longitude; 180 m above sea level) for 2012-2021 years with a more detailed analysis of the last six years from 2016 to 2021 years. Ozone measurements at the station are carried out using an APOA-370 gas analyzer (HORIBA, Japan) with an error of no more than 15 μg/m3.A significantly high-level air pollution of а near-surface ozone was revealed in the observation region, despite the absence of nearby sources of industrial emissions. The maximum hourly average concentration of ozone, equal to 195 µg/m3, was observed on 25.08.2018To interpret the results obtained, determine the nature of ozone pollution, its relationship with carbon monoxide, and the influence of transboundary and downward transport on ozone concentrations, observations data from the AIRS (Atmospheric InfraRed Sounder, Level 3, v.6 resolution 1°x1°, “ascending only”) orbital spectrometer were used.The relationship of near-surface ozone concentration and meteorological parameters was investigated. Wind directions leading to increased levels of near-surface ozone pollution are established. Intra-annual variations of near-surface ozone concentration are analyzed. Factors causing the local summer minimum of surface ozone level in some years are established.Using NOAA HYSPLIT trajectory model and ERA5 reanalysis, a spatial analysis of the atmospheric circulation pattern in the region was carried out. The recurrence of episodes of exceeding the ozone concentration 100 µg/m3 during more than 8 hours (WHO recommendation, further in the text - the standard) was estimated. The frequency of exceeding this standard is about 5% of all measurements for the time-period of 2016–2021. Possible causes of these episodes were determined and discussed. The mechanisms of long-range transport and its contribution to the near-surface ozone regime in the area of the station have been established in different seasons.Thus, trajectory analysis showed that for cases where the standard is exceeded in the spring, the movement of air masses occurs over the surface of Black Sea under cyclonic circulation processes. The analysis showed that polluted air masses were formed mainly over central Ukraine, Turkey, Romania and Bulgaria. In the summer months, atmospheric transport over the land surface from the eastern direction (Ukraine, southern Russia) predominates.Annual trends of near-surface ozone concentration in the period 2012-2021 years are estimated as statistically insignificant.Study was supported by Russian Science Foundation, Project No 20-17-00200.