## 4 Results
### The Spatiotemporal Patterns of the Exceedances of the Estimated MDA8
This pattern may be attributed to the region's distinct spatiotemporal  
Figure 5: Spatial patterns of MDAS exceedances (MDA8 \(>\) 160 \(\upmu\)g m\({}^{-3}\)) and the month with the largest MDA8 exceedances in the 2019–2021 period. (**a**–**c**) indicate the MDA8 exceedances in 2019, 2020, and 2021. (**d**–**f**) represent the spatial distribution of the months with the highest MDA8 exceedances in 2019, 2020, and 2021.  
variations in temperature, ultraviolet radiation, and precipitation [30; 40; 51; 52; 63]. The summer season, marked by increased temperatures, ample sunlight, and atmospheric stability, fosters the emission of VOCs and enhances the likelihood of photochemical reactions involving pollutants such as NO\({}_{\mathsf{X}}\), leading to the formation of ozone. Consequently, these trends indicate that future pollution control efforts should concentrate on summertime emission reductions to mitigate the incidence and severity of ozone pollution. Figure 6 presents the annual exceedance rate of ozone pollution for each month in the NCP from 2019 to 2021 as well as the annual cumulative number of ozone exceedances in each province. Figure 6a reveals the monthly exceedance rate of ozone pollution in the region over the three years period and indicates notable interannual variations and seasonal disparities in the ozone pollution levels within the NCP. Based on the monthly patterns of ozone pollution, June was identified as the month with the most pronounced ozone pollution, with an average exceedance rate of 42.65% from 2019 to June 2021. Apart from June, May was the second most polluted month, with an average exceeding rate of 16.90% from 2019 to 2021. Furthermore, September was recognized as the third most polluted month, with a three years average exceedance rate of 15.56%. In addition to these three months, April and July also experienced significant ozone pollution. In general, ozone pollution in China is predominantly observed during the summer months, followed by spring and then autumn. Regarding the annual trends in ozone pollution, a downward trajectory was noted for most months from 2019 to 2021 in the NCP. This decline may be correlated with the COVID-19 pandemic [53; 54] and is also attributed to the government's ongoing implementation of collaborative emission reduction policies for PM\({}_{2.5}\) and O\({}_{3}\) pollution [30; 64; 65; 66]. Among all months, June exhibited a trend of initial increase followed by a decrease in ozone pollution from 2019 to 2021, potentially due to the elevated temperatures in June 2021, which contributed to an upsurge in the net photochemical production of ozone [47; 48; 61; 62]. The main reasons for the ozone peak in June are high temperature and strong solar radiation. These conditions promote the photochemical generation of ozone, resulting in a significant increase in ozone concentration. In order to solve this problem, the following measures can be taken. First, strengthening the control of NO\({}_{\mathsf{X}}\) and VOCs emissions, implementing stricter industrial emission regulations, and promoting low-emission technologies can significantly reduce the emission of ozone precursors. Second, improving traffic management by optimizing traffic flow, promoting public transportation, and encouraging the use of electric vehicles, which can effectively reduce the emission of ozone precursors from traffic sources. Finally, promoting the use of clean energy over fossil fuels, as shifting to renewable energy sources such as wind, solar, and hydropower can reduce the overall ozone precursor emissions. Through these measures, the ozone peak in June can be effectively alleviated, and the air quality improved. Figure 6b presents the aggregate data on the frequency of ozone pollution exceedances across individual provinces within the NCP as well as in adjacent provinces. O\({}_{3}\) pollution was predominantly concentrated in Hebei, Shandong, and Henan Provinces, aligning with the findings depicted in Figures 4b and 5a-c.  
Figure 6: \(Cont.\)