Study On Optical Properties Of Atmospheric Aerosols In Lanzhou City

With the rapid development of China's economy and the acceleration of urbanization,the problem of air pollution has become increasingly prominent.In this study,the observation data of the Lanzhou site's solar photometer from July 2015 to June 2016 was used as the research object.The characteristics of aerosol optical depth and?ngstr?m parameters in Lanzhou area were analyzed and compared with satellite remote sensing data.At the same time,the special weather process was analyzed in combination with the results of air pollution monitoring in Lanzhou,and the changes of the corresponding atmospheric aerosol optical characteristics in the case of clean and different types of air pollution were discussed.Air mass trajectory is used to analyze the potential sources of pollutants in the affected ambient air quality in Lanzhou.These studies lead to the following conclusions:?1?The daily variation of aerosol optical depth in Lanzhou area is small.The aerosol optical depth value generally shows a stable trend of day and night low,reaching a peak at 9 o'clock.The diurnal variation trend of?ngstr?m parameters is consistent with the aerosol optical depth,and both are in a state of steady change.The daily maximum aerosol optical depth in different seasons appeared at the morning peak.Compared with the?ngstr?m wavelength index,the monthly changes of AOD_{550 nm} and atmospheric turbidity coefficient?are relatively stable and consistent,while the?ngstr?m wavelength index?varies greatly,and there is no obvious regularity with the change of aerosol optical depth.The optical depth of the atmospheric aerosol in Lanzhou area is high in winter?0.60±0.23?and low in summer?0.33±0.12?.The?ngstr?m wavelength index is higher in summer and autumn and winter?>1.0?,while it is smallest in spring?0.68±0.28?.?2?The aerosol type classification results show that the aerosol type has obvious seasonal changes.It is affected by sand aerosols in spring,and has obvious coarse modal particle distribution.It is relatively clean in summer,and the fine particle hygroscopicity increases significantly in autumn.At high aerosol optical depth,it is mainly affected by fine modal particles,and in winter it is affected by mixed aerosols of coarse particles and fine particles.The main type of aerosol in Lanzhou is mixed aerosol?61%?.Sand dust aerosols account for a relatively low proportion in Lanzhou,contributing only 4%throughout the year.The contribution of clean continental aerosols to the whole year is 20%,which indicates that the atmospheric quality of Lanzhou is good.?3?There is a seasonal variation in the spatial distribution of aerosol optical depth in Lanzhou area,which is significantly higher in spring than other seasons.The aerosol optical depth in Xigu District is the largest,and the aerosol optical depth in Yuzhong and its surrounding areas is small.The optical depth of aerosols in summer and autumn remained at a relatively low level.The spatial distribution of aerosols in Yongdeng County and Qilan County in summer was larger,but the opposite was true in autumn.The correlation between the MODIS-AOD inversion results and the foundation monitoring CE-318 AOD results in Lanzhou area is poor,and the correlation coefficient is only 0.44.However,most satellite remote sensing inversion AOD values are within the confidence interval,accounting for 69%of the total number of samples.The MODIS-AOD value of Lanzhou is underestimated and shows a certain seasonality.Most of the aerosol optical depth in autumn is underestimated.?4?The most obvious change of the six types of atmospheric pollutants during special weather is PM₁₀,and the smallest change is CO.PM_2.5 and NO₂ concentrations are highest in haze weather,and PM₁₀ concentration is highest in sandy episode.The concentration of SO₂ was the highest during the fireworks display period,and the concentration ratio of PM_2.5 to PM₁₀0 was the highest,which was 3.02 times the lowest value during the sandy weather.The average?ngstr?m wavelength index during sand and dust weather is only 0.18,which is 16%of clean weather,reflecting the dominant distribution of coarse particles in atmospheric aerosols during sand and dust episode.The value of the wavelength index is large during the haze event and during the fireworks display,and the fine-grained aerosols are dominant in the aerosols;during sand weather,the high AOD_{500 nm}?>0.8?and low?ngstr?m wavelength index?<0.6?are coupled,the atmospheric aerosols are dominated by coarse-grained sand-dust aerosols.?5?Different types of pollution episodes have different origins of air masses,and transport routes are also different.Except for the sand dust event,the trajectory paths of the other two pollution events come from different regions at different altitudes.During haze weather,the air mass that affects Lanzhou mainly comes from northwest China.During the fireworks display,the airflow that affects the air quality in Lanzhou mainly comes from the local and nearby areas.During the sand activities,the airflow trajectories affecting the Lanzhou area all come from western Mongolia,passing through the Gobi,Gurbantonggut Desert,Badain Jaran Desert and Tengger Desert.