| During recent years,the increase of aerosols has also led to the frequent occurrence of various pollution events and the decline of visibility,which has seriously harmed the natural environment and human health.Nanjing has a developed economy and numerous industrial areas.Therefore,it is of great scientific and practical significance to study the temporal and spatial distribution of aerosol characteristics and visibility in Nanjing.Firstly,based on MODIS and CALIPSO,this paper analyzed the aerosol characteristics in Nanjing from 2011 to 2018.It is found that the AOD in Nanjing had a downward trend in the past eight years.The AOD in Nanjing is the highest in winter and the lowest in spring and autumn.In spring,the AOD results of MODIS are larger than those of CALIPSO,while in autumn,the results of CALIPSO are slightly larger than those of MODIS.In winter and June,the atmosphere is dominated by coarse particles,while in autumn,the content of coarse particles is the lowest.In winter,the atmosphere is dominated by absorption aerosol particles,and in summer,the atmosphere is dominated by non-absorption aerosol particles.In summer,the atmosphere is dominated by regular particles,and the other three seasons are dominated by irregular particles.The lower atmosphere is dominated by large particles,and the number of fine particles in the middle and upper layers is increasing gradually,the size of particles in each height layer is less affected by the month.Then we analyzed a June 2018 Nanjing haze event using ground-based and spaceborne sensors,with the ground-based and spaceborne sensor data exhibiting good consistency.Water vapor content showed significant positive correlation with AOD,and AOD measured in urban and industrial areas was much higher compared to other similar zones.The afternoon convection caused the aerosol uplift during the haze event.Higher aerosol concentration was detected below 2 km.Pollutants at high altitude were dominated by small particles,while the overall pollutant mix was dominated by mixed aerosols.During a stable period over June 11–18,a single,near-surface inversion layer,and occasional two inversion layers,stopped pollutant dispersal,with only very stable ocean air mass transport in the southeast direction available.The AQI drop which took place during June 28–30 was caused by two inversion layers,combined with the immigration of pollutants from inland air masses.Finally,by using CALIPSO data,the temporal and spatial distribution of visibility at different heights in Nanjing was analyzed.In spring,the visibility distribution at 0?4km is increasing fluctuatly with height;the distribution of aerosols at 0?3km is uneven,and the distribution of aerosols above 3km is even.In summer,the minimum value of visibility occurs at about 3km within 0?4km;the aerosol distribution at 0?1km,2?3km and 4?8km is uneven,and the aerosol distribution of other heights is even.In autumn,the fluctuation of visibility at 0?4km is the largest in four seasons;the distribution of aerosols at 0?4km is uneven,and the distribution of aerosols above 4km is even.In winter,the visibility fluctuation at 2?4km in the lower layer is greater than that of 1?2km,and the visibility is generally distributed within 20 km,which is the lowest in four seasons;the v aerosol distribution at 0?2.5km is uneven,and the aerosol distribution above 2.5km is even.It is noted that the visibility above 8km in four seasons is greater than 100 km,and there is no aerosol above 8km.During the pollution period,the concentration height of aerosols is much higher than that during the non-pollution period,and the visibility at low altitude is generally distributed in the range of 5?20km;during the nonpollution period,the visibility can rapidly increase to more than 100 km above the aerosol concentration layer. |
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