Long-Term Variability of Surface Ozone and Its Associations with NOx and Air Temperature Changes from Air Quality Monitoring at Belsk, Poland, 1995-2023

Surface ozone (O-3) and nitrogen oxides (NOx = NO + NO2) measured at the rural station in Belsk (51.83 degrees N, 20.79 degrees E), Poland, over the period of 1995-2023, were examined for long-term variability of O-3 and its relationship to changes in the air temperature and NOx. Negative and positive trends were found for the 95th and 5th percentile, respectively, in the O-3 data. A weak positive correlation (statistically significant) of 0.33 was calculated between O-3 and the temperature averaged from sunrise to sunset during the photoactive part of the year (April-September). Recently, O-3 maxima have become less sensitive to temperature changes, reducing the incidence of photochemical smog. The ozone-climate penalty factor decreased from 4.4 mu g/m(3)/degrees C in the 1995-2004 period to 3.9 mu g/m(3)/degrees C in the 2015-2023 period. The relationship between O-x (O-3 + NO2) and NOx concentrations averaged from sunrise to sunset determined the local and regional contribution to O-x variability. The seasonal local and regional contributions remained unchanged in the period of 1995-2023, stabilizing the average O-3 level at Belsk. "NOx-limited" and "VOC-limited" photochemical regimes prevailed in the summer and autumn, respectively. For many winter and spring seasons between 1995 and 2023, the type of photochemical regime could not be accurately determined, making it difficult to build an effective O-3 mitigation policy.