Application of roadside air purifiers in urban street canyons: A pilot-scale study in Hong Kong

Xinwei Li; Shuwen Han; Pengge Wang; Han Mei; Zhi Ning; Fan Dong; Long Cui; Yu Huang; Tao Wang; Shao-Yuan Leu; Meng Wang; Shun-Cheng Lee

doi:10.1016/j.scitotenv.2023.168671

Application of roadside air purifiers in urban street canyons: A pilot-scale study in Hong Kong

Sci Total Environ. 2024 Feb 20:912:168671. doi: 10.1016/j.scitotenv.2023.168671. Epub 2023 Nov 22.

Authors

Xinwei Li¹, Shuwen Han¹, Pengge Wang², Han Mei³, Zhi Ning³, Fan Dong⁴, Long Cui², Yu Huang⁵, Tao Wang¹, Shao-Yuan Leu¹, Meng Wang¹, Shun-Cheng Lee⁶

Affiliations

¹ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
² State Key Laboratory of Loess and Quaternary Geology (SKLLQG) and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
³ Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
⁴ Research Center for Carbon-Neutral Environmental & Energy Technology, Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China.
⁵ State Key Laboratory of Loess and Quaternary Geology (SKLLQG) and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China. Electronic address: huangyu@ieecas.cn.
⁶ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China; Thrust of Earth, Ocean and Atmospheric Sciences Function Hub, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, China. Electronic address: shun-cheng.lee@polyu.edu.hk.

PMID: 37996025
DOI: 10.1016/j.scitotenv.2023.168671

Abstract

The implementation of roadside air purifiers has emerged as an effective active control measure to alleviate air pollution in urban street canyons. However, technical questions raised under real conditions remain challenging. In this study, we conducted a pilot-scale investigation involving seven units of self-designed roadside air purifiers in an urban street canyon in Hong Kong. The air cleaning effects were quantified with an air quality sensor network after rigorous quality control. The removal efficiencies of Nitrogen dioxide (NO₂), Fine suspended particulates (PM_2.5), Carbon monoxide (CO), and Nitric oxide (NO) were determined by comparing with simultaneously measured ambient concentrations, with hourly average efficiencies of 14.0 %-16.9 %, 3.5-10.0 %, 11.9 %-18.7 %, and 19.2 %-44.9 %, respectively. Generally, the purification effects presented variations depending on the ambient pollutants' levels. Higher ambient concentrations of NO₂, PM_2.5, CO correlated with increased purification effects, while NO presented the opposite trend. The influence of interval distance combined with spatial distribution indicated the operation of purifiers will induce local NO₂ attenuation even at an interval distance of four meters. Statistical analysis delivered evidence the air cleaning ability exhibited optimal performance when relative humidity level is ranged from 70 % to 90 %, aligning with the prevailing conditions in Hong Kong. Additionally, improved purification effects were observed at the downwind direction, and their performance was enhanced when the wind speed exceeded 2.5 m/s. Moreover, we estimated the operational lifetime of the air purifiers to be approximately 130 days, offering crucial information regarding the filter replacement cycle. This work serves as a pioneering case study, showcasing the feasibility and deployment considerations of roadside air purifiers in effectively controlling air pollution in urban environments.

Keywords: Hong Kong roadside; Meteorological variables; Roadside air purifiers; Urban air pollution.