Comparison of particle concentration vertical profiles between downtown and urban forest park in Nanjing (China)

This study attempts to characterize and compare the vertical distributions of the PM2.5 and PM10 concentrations in downtown and surrounding national forest park. A contrastive measurement was performed using the portable particle sampler in Nanjing (China), from Apr. 22, 2016 to Jan. 24, 2017. The particle concentrations were found to be negatively associated with height in the forest park. The same but slighter phenomena were also found in the downtown in most time, however, peak values were observed at the height of roadside tall tree (25 m) instead of at the ground level at most of the sampling time. At 100 m, particle concentrations decreased by about 30% in the forest park, and only a 20% attenuation was found in the downtown. An unmanned aerial vehicle (UAV) measurement was conducted under the hypothesis that the roadside trees can limit the vertical diffusion of particles. It was found that the interception of trees could reduce 24% and 26% of the PM2.5 and PM10 concentrations above the road, respectively. The correlation analysis between the particle concentrations and five meteorological parameters (temperature, relative humidity, air pressure, solar energy and precipitation) showed higher correlations in the downtown than in the forest park. Both the temperature and the relative humidity contributed to the variation of the particle concentrations at different heights. This work serves to better understanding of particles dynamic characteristics in urban areas and has a significant implication for assessment of indoor air quality in high-rise buildings.