The North China Plain (NCP) has become one of the most polluted regions inChina, with the rapidly increasing economic growth in the past decades. Highconcentrations of ambient O and aerosol have been observed at urban aswell as rural sites in the NCP. Most of the in situ observations of airpollutants have been conducted near the ground so that current knowledgeabout the vertical distributions of tropospheric O and aerosol over theNCP region is still limited. In this study, vertical profiles of O andsize-resolved aerosol concentrations below 2.5 km were measured insummer 2014 over a rural site in the NCP, using an unmanned aerial vehicle(UAV) equipped with miniature analyzers. In addition, vertical profiles ofaerosol scattering property in the lower troposphere and vertical profiles ofO below 1 km were also observed at the site using a lidar and tetheredballoon, respectively. The depths of the mixed layer and residual layer weredetermined according to the vertical gradients of lidar particle extinction andaerosol number concentration. Average O and size-resolved aerosolnumber concentration in both the mixed and residual layer were obtained fromthe data observed in seven UAV flights. The results show that during most ofthe flights the O levels above the top of mixed layer were higher thanthose below. Such a positive gradient in the vertical distribution of O makesthe residual layer an important source of O in the mixed layer,particularly during the morning when the top of mixed layer is rapidly elevated.In contrast to O, aerosol number concentration was normally higher inthe mixed layer than in the residual layer, particularly in the early morning.Aerosol particles were overwhelmingly distributed in the sizerange 1 µm, showing slight differences between the mixed andresidual layers. Our measurements confirm that the lower troposphere overthe rural area of the NCP is largely impacted by anthropogenic pollutantslocally emitted or transported from urban areas. Compared with the historicO vertical profiles over Beijing from the Measurement of Ozone andWater Vapor by Airbus In-Service Aircraft (MOZAIC), a strong increase inO can be found at all heights below 2.5 km in the decade from 2004 to2014, with the largest enhancement of about 41.6 ppb. This indicates that thelower troposphere over the northern part of the NCP has experienced rapidlyworsening photochemical pollution. This worsening trend in photochemicalpollution deserves more attention in the future.
展开▼
