Measurement Study of Diurnal Variations of PM2.5 Mass Concentrations and Affecting Factors on Pollutant Dispersion in Urban Street Canyons under Weak-Wind Conditions in Xi’an

Yun-Wei Zhang,Zhen-Xing Shen,Shun-Cheng Lee,Yan Cheng,Jun-Gang Dong,Zhao-Lin Gu

doi:10.4209/aaqr.2011.11.0215

Abstract

Daytime variations of PM2.5 concentration in three street canyons in Xi’an were measured during June 11–15, 2010. Weather conditions, including the ambient wind condition and the street canyon air temperature, were also recorded. These measurements were conducted on weak-wind summer days, when the mean ambient wind velocity was 1.26 m/s. The results show that, under weak-wind conditions, there were no good correlation between PM2.5 concentrations and vehicle flux inside the street canyons. The vehicle related PM2.5 concentrations accumulated in the daytime inside the street canyons. The PM2.5 concentrations at the pedestrian level were of near uniform horizontal distribution. These results indicate the absence of the typical primary air flow re-circulation inside the street canyons under weak-wind conditions, and that the dispersion and transportation of vehicle exhausts inside and/or outside the street canyons are influenced by vehicle induced air flow and thermal induced buoyancy.

Highlights

The links between certain respiratory health issues, such as the increase in asthma cases and mortality, and suspended particulate matter (Ali-Toudert and Mayer, 2006) in the atmosphere, especially in urban environments have been established by epidemiological and toxicological studies (Nag et al, 2005; Cooke et al, 2007)
The results show that, under weak-wind conditions, there were no good correlation between PM2.5 concentrations and vehicle flux inside the street canyons
These results indicate the absence of the typical primary air flow re-circulation inside the street canyons under weak-wind conditions, and that the dispersion and transportation of vehicle exhausts inside and/or outside the street canyons are influenced by vehicle induced air flow and thermal induced buoyancy

Summary

Introduction

The links between certain respiratory health issues, such as the increase in asthma cases and mortality, and suspended particulate matter (Ali-Toudert and Mayer, 2006) in the atmosphere, especially in urban environments have been established by epidemiological and toxicological studies (Nag et al, 2005; Cooke et al, 2007). It is important to understand the dispersion and diurnal variation characteristics of pollutants in the street canyons under various urban meteorological conditions, to formulate effective strategies such as positioning of ventilation air intake, for emission control; and for urban planning. Several methods, such as laboratory-scale experiments (Pavageau and Schatzmann, 1999; Ahmad et al, 2005), in-situ. Measurements and simulations of the air flow and pollutant distributions and dispersions under weakwind conditions are relatively rare

Methods

Results

Conclusion