Intraurban distributions of NO_2 and PM_(2.5) at three dimensions in Lanzhou, China

摘要

Previous research linked maternal exposures to NO_2 or PM_(10) with increased risks of adverse birth outcomes in Lanzhou. To improve exposure assessment, a land use regression study at ground level with consideration of vertical variation by building height was conducted in Lanzhou. In each of four seasons in 2016-2017, NO_2 was measured using Ogawa badges for 2 weeks at 75 ground-level sites. PM_(2.5) was measured using DataRAM at a subset (N=38) of the 75 sites. The PM_(2.5) monitor was systematically moved in pre-determined patterns around each site. The measurements were adjusted for temporal trend using government monitoring data. Vertical profile measurements were conducted at 18 sites evenly distributed at increasing floors of 2 buildings: one facing traffic and the other facing away from traffic. The annual and seasonal concentrations of NO_2 and PM_(2 5) at ground level were regressed against spatial predictors, including elevation, population, road network, land cover, and land use with buffers 100-2000 m around each site. The vertical variations were investigated using polynomial models. NO_2 concentrations were associated with lengths of major roads and of all roads, slope, and cultivated land (adjusted R~2: 0.61). PM_(2.5) concentrations were higher in certain districts, and associated with population density, lengths of roads with vehicles, and elevation (adjusted R~2: 0.56). From the 1st to 32nd floors in the building facing traffic, NO_2 and PM_(2.5) concentrations decreased 22% and 26%, respectively. These distributions showed seasonal and diurnal variations. The ground-level NO_2 and PM_(2.5) showed different patterns, which was not captured by the 4 government monitors in Lanzhou. Concentrations of these pollutants decreased substantially with height. Therefore, characterizing 3-dimensional distributions of multiple pollutants might be crucial for exposure and risk assessment in cities with mixed pollution sources and tall buildings, and potentially have policy implications.