The effect of urban morphological characteristics on the spatial variation of PM2.5 air quality in downtown Nanjing.

Tom V Kokkonen,Tuukka Petäjä,Aijun Ding,Bo Wang,Derong Zhou,Veli-Matti Kerminen,Yuning Xie,Markku Kulmala,Jianning Sun,Pauli Paasonen,Wei Nie,Wei Qin,Lin Jiang,Shahzad Gani

doi:10.1039/d1ea00035g

Abstract

The effects of the urban morphological characteristics on the spatial variation of near-surface PM2.5 air quality were examined. Unlike previous studies, we performed the analyses in real urban environments using continuous observations covering the whole scale of urban densities typically found in cities. We included data from 31 measurement stations divided into 8 different wind sectors with individually defined morphological characteristics leading to highly varying urban characteristics. The urban morphological characteristics explained up to 73% of the variance in normalized PM2.5 concentrations in street canyons, indicating that the spatial variation of the near-surface PM2.5 air quality was mostly defined by the characteristics studied. The fraction of urban trees nearby the stations was found to be the most important urban morphological characteristic in explaining the PM2.5 air quality, followed by the height-normalized roughness length as the second important parameter. An increase in the fraction of trees within 50 m of the stations from 25 percentile to 75 percentile (i.e. by the interquartile range, IQR) increased the normalized PM2.5 concentration by up to 24% in the street canyons. In open areas, an increase in the trees by the IQR actually decreased the normalized PM2.5 by 6% during the pre-COVID period. An increase in the height-normalized roughness length by the IQR increased the normalized PM2.5 by 9% in the street canyons. The results obtained in this study can help urban planners to identify the key urban characteristics affecting the near-surface PM2.5 air quality and also help researchers to evaluate how representative the existing measurement stations are compared to other parts of the cities.

Highlights

The rapid industrialization and urbanization have led to many environmental problems in China.[1,2,3,4] As a consequence of this rapid development, eastern China is one of the most populated areas in the world which suffers from atmospheric pollution especially in urban areas.[5,6] The air pollutants have been estimated to cost over 1 million lives annually in China[7] and ne particulate pollutants have been identi ed as one of the most harmful air pollutants in terms of human health.[8,9,10]The air quality can vary substantially in different parts of the city
When the stations located in the open areas were examined, the effect of z0/zH was much smaller on the normalized PM2.5 concentration than it was for the street canyons (Fig. 4b and Table 2), but it was still signi cant (p-value < 0.01)
This was quite expected since the increased surface roughness due to the increased z0/zH in the upwind direction could induce more turbulence and even bene t the ventilation of open areas, whereas the increasing z0/zH was clearly deteriorating the PM2.5 air quality in the street canyons

Summary

Introduction

The rapid industrialization and urbanization have led to many environmental problems in China.[1,2,3,4] As a consequence of this rapid development, eastern China is one of the most populated areas in the world which suffers from atmospheric pollution especially in urban areas.[5,6] The air pollutants have been estimated to cost over 1 million lives annually in China[7] and ne particulate pollutants have been identi ed as one of the most harmful air pollutants in terms of human health.[8,9,10]The air quality can vary substantially in different parts of the city.

Methods

Results

Discussion

Conclusion