Study On The Seasonal Characteristics Of Solar Radiation And Its Impact On Near-Surface Ozone In Hefei City

Ground-level ozone is primarily the product of photochemical reactions between primary pollutants such as nitrogen oxides and volatile organic compounds in the atmospheric environment.In addition to being influenced by precursor concentrations,changes in ozone are directly related to solar radiation.It is crucial to clarify the relationship between solar spectral irradiance（SSI）and ozone concentration,and to reveal the response of ozone concentration to changes in solar radiation,in order to scientifically understand the formation mechanism of ground-level ozone pollution and take effective measures to mitigate it.In order to investigate the seasonal characteristics of solar radiation and its impact on ozone concentration in the Hefei region,this study used an MS-711 solar radiation meter to measure the spectral solar irradiance（SSI）from 300 nm to 1100 nm during four typical months in Hefei.Environmental monitoring data on O3 from 10 national monitoring stations in Hefei were analyzed to examine the seasonal and diurnal characteristics of solar radiation.Combining the patterns of ozone concentration changes,the correlation between ozone concentration and solar radiation was analyzed,and the influence of solar radiation on ozone concentration was discussed under different weather conditions.Next,using the new generation environmental air quality model WRF/CAMx,the Integrated Process Rate（IPR）method was employed to quantitatively calculate the contribution of various physical and chemical processes to changes in ozone concentration in the Hefei region and to analyze the role of solar radiation in these processes.Firstly,the characteristics of SSI in Hefei and its variations under different weather conditions were analyzed.The observation showed that the monthly average SSI in Hefei ranked from high to low in the order of July,April,October,and January,and the monthly maximum average SSI appeared at a frequency of around 470nm.The visible light band radiation energy accounted for more than 61%,followed by the infrared band,which accounted for more than 30%.The proportion of visible and ultraviolet radiation energy increased in July.The proportion of infrared radiation on cloudy days was higher than that on other weather conditions.In January,the average proportion of infrared radiation on sunny days was 4%to 7%higher than that on other weather conditions,and the proportion was 2%in July.Secondly,the characteristics of ozone pollution in Hefei and its distribution in different weather conditions were analyzed.It was found that the ground-level ozone pollution in Hefei has obvious seasonality,with June being the most severe.Ozone pollution also exhibits obvious spatial patterns,with higher concentrations observed at sites such as Huangpu Mountain Villa,Binhu New District,High-tech Zone,and Dongpu Reservoir compared to other locations,and pollution is more likely to occur in spring,summer,and autumn.During the day,Hefei’s ozone concentrations exhibit a single-peak pattern,with the peak time changing with time and season.At night,ozone concentrations in Hefei typically decline continuously from 18:00 to 23:00 and then remain stable after24:00.Ozone concentrations in January and July are higher on sunny days than on cloudy or rainy days,and are correlated with solar radiation.Ozone is negatively correlated with NO2 and CO in all seasons.Ozone is positively correlated with PM2.5 in summer but negatively correlated in other seasons.Thirdly,the impact of time lag of solar irradiance on ozone was evaluated.Time lagged cross-correlation（TLCC）analysis revealed a significant positive correlation between ground-level ozone concentration and solar irradiance（325nm～400nm）.The response time of ground-level ozone concentration to solar radiation was approximately3 hours,with the maximum correlation coefficient between ozone concentration and solar radiation occurring at a lag of 3 hours.The lag time corresponding to the maximum correlation coefficient varied with different seasons,with the maximum impact occurring at lag（2）and lag（3）in July.The lagged correlation was weakest during sunny summer days,and strongest during cloudy,rainy,and sunny winter days.Fourthly,a simulation study was conducted to investigate the physical and chemical processes affecting ozone in the Hefei region and their relationship with solar radiation.The numerical simulation results confirm that the peak of ozone（O₃）concentrations during summer daytime occurs approximately 2-3 hours after the peak of solar radiation intensity.The correlation coefficient obtained from the simulation results is higher than the observed results.The reason for this is that in the actual process,the photochemical reactions of O₃ are also constrained by precursor emissions,which weakens the direct impact of solar radiation on O₃ concentrations.Atmospheric vertical motion contributes in opposite ways to near-surface O3 concentrations on clear and rainy days.Under different weather conditions,the diurnal variation of ozone concentration is closely related to the contributions of several mechanisms.On clear days,the accumulation of O₃ primarily comes from photochemical processes.After the decrease in solar radiation intensity,a significant input of O₃ from the upper boundary layer becomes a key factor in maintaining O₃ concentrations.During rainy days,the growth and maintenance of O₃ concentrations throughout the afternoon period mainly depend on the contributions through vertical transport across the upper boundary.On cloudy days,solar radiation dominates the phase of O₃ growth,while dry and wet deposition as well as horizontal flux dominate the phase of O₃decline.Based on the above studies,this article obtained the SSI characteristics of ozone concentration in Hefei and found the lag effect of solar radiation on ozone concentration.The seasonal variation of solar radiation and its lagged correlation with ozone concentration under different weather conditions were described,and the physical and chemical processes that affect ozone concentration and their relationship with solar radiation were revealed.These findings are of great significance for a deeper understanding of the generation mechanism of ozone pollution in Hefei and the scientific formulation of ozone pollution prevention and control measures.