Mobile observations of air pollution characteristics and source tracking : the case of Megacity Chengdu, China

Precise pollution control and source tracking have been commonly used due to the development of portable on-line sampling instruments. This study investigated the spatial distribution characteristics of pollution during a local pollution period in the Shuangliu district of Chengdu, China. The persistent particle size distributions and ozone concentrations in the Shuangliu district were recorded using a mobile observation platform. The three-dimensional spatial and temporal changes in the aerosol size distributions and ozone concentrations were obtained by means of a portable optical particle profiler (POPS), a PO3M ozone detector, a hand-held meteorological station, and a Laser wind lidar. The results indicate that during polluted episodes, the daily particle number concentration (PNC) values ranged from 7,967.63 to 16,342.31 #·cm-3, compared to 4,290.87 to 11,039.61 #·cm-3 during clean episodes. The results revealed that human activities and meteorological conditions were the primary causes of local pollution. Regarding regional transport, 80% of the total particle pollution was likely to occur under the influence of northerly winds and came from the industrial emissions and human activities in upwind areas. Indeed, there are certain relationships between the planetary boundary layer height, the vertical wind direction and speed, and between the planetary boundary layer height and the number concentrations of different particle size ranges. According to the backward trajectory analysis, the industrial cities in northeastern Chengdu, Chongqing Province, were identified as the major regional sources of particle emissions in winter. Our results provide a scientific basis for the control of particulate matter and ozone in the Shuangliu district, which enables targeted pollution prevention and control measures by the relevant departments.