| Because particulate matter has a long life,it is usually carried downwind.More than 1000 observation stations have been established nationwide,and the distribution of aerosols has been basically obtained.However,because this transport phenomenon is not limited to the near surface,and is very strong in the upper boundary layer and even in the free atmosphere,it cannot be captured by observation only close to the ground.At present,it is urgent to develop real-time online observation methods to study the vertical profile of aerosols,so as to serve the prevention and control of air pollution in China.Multiaxial differential optical absorption spectroscopy(MAX-DOAS),as a real-time,online and continuous observation method,has become a hot topic at present,but its applicability has not been effectively evaluated.In 2019,the vertical profile of atmospheric spectrum in Beijing area was observed by ground-based MAX-DOAS at the Institute of Atmospheric Physics,Chinese Academy of Sciences.Based on the optimal estimation method(OEM)and the least square spectral fitting method,the vertical profile of the aerosol extinction coefficient was obtained by using Heidelberg profile(Heipro)algorithm,and the aerosol optical thickness(AOD)was obtained by integrating the aerosol extinction coefficient along its path.In order to verify the applicability of MAX-DOAS in monitoring aerosol profiles,the column concentration of the backscattering coefficient observed by ground-based solar photometer and cloud altimeter was compared with the total column concentration observed by MAX-DOAS.The vertical profile of particle mass concentration observed from high tower and the vertical profile of aerosol extinction coefficient of MAX-DOAS were compared at 0?300m.The backscattering coefficient observed by cloud altimeter was compared with the vertical profile of the aerosol extinction coefficient of MAX-DOAS at 300?4000m,so as to verify the applicability of MAX-DOAS in different seasons,different pollution processes and different spatial scales.The aerosol vertical profile data set was obtained,and the aerosol vertical evolution law was analyzed.The main results of this study are as follows:(1)The aerosol column concentration observed by MAX-DOAS was strongly correlated with that observed by solar photometer and ceilometer,which were 0.9 and0.8,respectively,indicating that the observation of MAX-DOAS column concentration had high accuracy.The data of tower gradient and vertical profile of ceilometer show that during the heavy haze and photochemical generation period,the aerosol profile observed by MAX-DOAS presents high correlation with tower gradient observation,the correlation is up to 0.9 and 0.85,and the correlation with vertical profile of laser ceilometer is also high when it is below 1km,both of which can reach about 0.8.While the aerosol profile has a good response to fine dust,it is found that the correlation between the aerosol profile and the tower gradient observation data and the vertical profile of the laser ceilometer altitudes decreases most obviously at high altitude.(2)Using the verified aerosol vertical profile data,the seasonal variation rule of the aerosol profile was obtained.It was found that the aerosol profile showed an exponential trend of decline with height,and the average aerosol extinction coefficient(AET)showed a situation that first decreased and then increased in the surface layer(except in winter).However,it showed different patterns in different seasons.The decreasing rate was the slowest in summer,from 0.34km-1 to 0.15km-1 at the altitude of 0-2 km,and the fastest in winter,from 0.31km-1 to 0.13km-1 at the altitude of 0-1km.Meanwhile,the aerosol extinction coefficient was the highest at the altitude in summer.Through the data set obtained,the diurnal variation of AOD and aerosol extinction coefficient profile was studied.In spring and winter,there was a change of "low in the morning and high in the afternoon",while in summer and autumn,the change was just the opposite,and the turning point of such change all occurred at 12:00.Compared with previous studies,this study has the following innovations: using a variety of vertical observation methods,this study evaluated the applicability of MAXDOAS inversion of aerosol profiles,obtained a complete annual aerosol vertical profile data set in Beijing area,and analyzed its vertical evolution rule. |
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