| With development of economy, the aerosol pollutants due to the anthropogenicemissions have gotten more and more attentions in China. Especially when there arelong-range transport of dust in spring, many cities suffer more serious andcomplicated air pollution problems. MPL (Micro Pulse Lidar) system with Fernaldalgorithm can retrieve the aerosol vertical distribution, which provides a good way tostudy optical characteristics of aerosol during the air pollution episode.In this study, data from various monitoring instruments was used to evaluate theresults from the MPL. The spatial and temporal distribution of PBL and aerosoloptical characteristics retrieved from lidar system, together with the meteorologicaldata and aerosol monitoring data, were used to analyze the urban air pollutionprocesses including the causes, the sources, and the regional transport processes. Theconclusions are listed as follows:1. The results from the MPL are comparable with the data from other monitoringinstruments. The changes in the PBL can be reflected by the lidar system accuratelyand quickly. The correlation of height of PBL from the lidar system with the LidarCeilometer was0.95during the clean days, while it was0.58during the air pollutionepisode. The lidar system matched the microwave radiometer well in determining theposition of extinction layer and the nature of extinction particle. The trends of thelight extinction coefficient of aerosol in330m agreed well with the light extinctioncoefficient and the concentration of PM2.5measured on the ground, and thecorrelations were0.77and0.75respectively.2. The aerosol pollution background of Beijing from December2012toNovember2013was counted in this study. In this period, there were twice strong dustprocesses with8hours totally and there were3851hours (46%of our study period)with haze. The sequence of seasons according to the hours of haze was as follows: summer> autumn> winter> spring. The frequency of dry haze was higher than damphaze which causes worse visibility. There was more serious haze in autumn andwinter than in summer and spring. The days with AQI higher than3level were55%of this study period and were major in the autumn and winter. The primary pollutantwas fine particulate matter in this period. The low visibility was consistent with thehigh AQI, which indicates the visibility could be used to reflect the aerosol pollution.3. The measured results from the MPL during a dust aerosol pollution processindicated that the dust was above the PBL in the early of this process because of thelow height of PBL. During this process, the dust depolarization ratio on the groundlevel increased to0.4and the thickness of dust was up to3km. The light extinctioncoefficient during this process was0.8km-1less than it in the haze days without dust.The height of PBL is up to904m. The results of HYSPLIT suggested that thelong-range transport of dust from Mongolia and the raising of local dust caused bywind should be responsible for this dust process.4. During the study of a serious haze process by MPL, the average PBL heightwas only293m, when91%of the time it was less than500m. Extinction coefficient ofeach vertical height reached more than1.5km-1above the ground. By comparing theanalysis of the aerosol depolarization ratio, we found that the atmospheric extinctionabove the city was caused by the combined effect of particulate aerosols andatmospheric moisture. The aerosol optical depth (AOD) at532nm in this severe hazeevent was high and affected by the relative humidity greatly. In lower RH, the valueof AOD was contributed by particulate aerosols, and atmospheric moisture made asignificant contribution due to the hygroscopicity of fine particle when the RH washigh. The ground and high altitude meteorological data analyzed with the MODISdata shows that continuous static stability is the immediate cause of what happened inthe haze process, the regional pollution and high humidity made the haze more worse. |
PDF Full Text Request