Surface ozone in Sapporo varies dynamically seasonally according to the meteorological conditions, which are (i) solar radiation which affects photochemical production of ozone; and (ii) regional-scale airflow, particularly the East Asian Monsoon, which affects the transport of ozone and its precursors. The general seasonal variation is characterized by a high peak in spring and lower peak in autumn, and lows in summer and winter. Inter-annually, surface ozone showed a general increase from 1980 to 2024. During COVID-19, seasonal variabilities have been noticeably smaller. A sharp drop was observed in post-COVID 2023 at Sapporo Center station, the only station in the urban area of the city. We found that ozone there has been generally lower, highly likely to be due to relatively high NOx (nitrogen oxides) levels. There is also a regime shift from NMHC (non-methane hydrocarbon)-limited to NOx-limited regime in recent years. We moved to reanalysis data to address spatial variability and also extend to the East Asian region. Unfortunately, chemical reanalysis was unable to provide satisfactory results for surface ozone. On the other hand, considering other pollutants in understanding tropospheric ozone is also important, so we add NO2 into our scope of interest. Hence, the next focus of my Doctor Course research is the Pandora instrument at the graduate school rooftop, a spectrometer that provides total column and vertically resolved concentrations of trace gases, mainly NO2 and also total O3. The Japan Pandora Network was launched under the GOSAT-GW Satellite project for NO2 validation. We also installed a CAPS-NO2 instrument for data validation and comparison.