Numerical Study On The Effect Of Aerosol On Tropospheric Photochemistry

The photolysis of tropospheric ozone(O3)and nitrogen dioxide(NO2)directly affect the atmospheric oxidation capacity and formation of secondary aerosols.In this paper,the influencing factors of photolysis rates of O3 and NO2(J[O1D]and J[NO2])were studied.We conducted some sensitivity experiments using a radiative transfer model(TUV)to quantify the effect of individual factors on photolysis rates.And the effects of the relative position between aerosols and clouds on the vertical profiles of photolysis rates and actinic flux were analyzed Through the survey,we hoped to determine the key factors affecting the tropospheric J[O1D]and J[NO2].The results showed thatThrough the analysis of observations,it was found that the aerosol optical depth(AOD)had the opposite trend with the photolysis rates.The larger cloud optical depth(COD)prevented actinic flux from reaching the ground,and higher relative humidity and lower temperature might also inhibit the process of photochemical reactions in the atmosphere,resulting in a decrease in photolysis rates near the ground.The offline radiative transfer model TUV captured the characteristics of the change of photolysis rates over time and the optical properties of environment,and the correlation coefficients of the simulation results and the observation data of J[O1D]and J[NO2]were larger than 0.9.WRF-Chem performed slightly poorer than the offline TUV in the simulation of photolysis rates,which may be related with the choice of emission inventory and schemes such as aerosols and chemistryThere were obvious differences in the influence of the optical properties of aerosols on the photolysis rates.On condition of a certain AOD,the stronger the scattering property of aerosols was,the larger the photolysis rates would be.When AOD increased by 2 units,the maximum values of J[O1D]and J[NO2]decreased by 30.3%and 13.1%,respectively.The presence of aerosols had a more pronounced effect on the photolysis reaction excited by shorter wavelength(J[O1D]),but the time difference of the influence of aerosols on the photolysis reaction excited by longer wavelength(J[NO2])was more significant.The photolysis rates were sensitive to changes of the smaller cloud optical depths.There was a significant difference in the time of the clouds influencing photolysis rates(J[O1D]and J[NO2]).In the vertical direction,the presence of clouds could reduce the actinic flux through the clouds,effectively reducing the photolysis rates under the clouds,while the backscattering properties of cloud droplets would increase the photolysis rates above the clouds.The absorption band of O3 was around 300 nm,so the total ozone content(TOC)played an important part in the photolysis of O3(J[O1D])When TOC increased from 200 DU to 400 DU,the maximum value of J[O1D]decreased by 53.1%,and that of J[NO2]decreased by only 1.0%The change of the relative position of aerosols and clouds had a conspicuous influence on the vertical distribution of tropospheric photolysis rates and actinic flux.When scattering aerosols were located above the cloud layer,the photolysis rates at high levels were significantly increased,and the backscattering properties of cloud droplets in the clouds below slowed down the rate of descending of the photolysis rates in the aerosol layer.When the absorbing aerosols were located above the cloud layer,the actinic flux in the upper layer was greatly attenuated,and the influence of the clouds on the photolysis rates was weak in this situation.