Effects of urban functional fragmentation on nitrogen dioxide (NO2) variation with anthropogenic-emission restriction in China

Yuan Meng,Hanfa Xing,Rui Zhu,Kwon Ho Lee,Mei-Po Kwan,Kai Qin,Coco Yin Tung Kwok,Man Sing Wong,Hon Li

doi:10.1038/s41598-021-91236-w

Abstract

Urban functional fragmentation plays an important role in assessing Nitrogen Dioxide (NO2) emissions and variations. While the mediated impact of anthropogenic-emission restriction has not been comprehensively discussed, the lockdown response to the novel coronavirus disease 2019 (COVID-19) provides an unprecedented opportunity to meet this goal. This study proposes a new idea to explore the effects of urban functional fragmentation on NO2 variation with anthropogenic-emission restriction in China. First, NO2 variations are quantified by an Autoregressive Integrated Moving Average with external variables-Dynamic Time Warping (SARIMAX-DTW)-based model. Then, urban functional fragmentation indices including industrial/public Edge Density (ED) and Landscape Shape Index (LSI), urban functional Aggregation Index (AI) and Number of Patches (NP) are developed. Finally, the mediated impacts of anthropogenic-emission restriction are assessed by evaluating the fragmentation-NO2 variation association before and during the lockdown during COVID-19. The findings reveal negative effects of industrial ED, public LSI, urban functional AI and NP and positive effects of public ED and industrial LSI on NO2 variation based on the restricted anthropogenic emissions. By comparing the association analysis before and during lockdown, the mediated impact of anthropogenic-emission restriction is revealed to partially increase the effect of industrial ED, industrial LSI, public LSI, urban functional AI and NP and decrease the effect of public ED on NO2 variation. This study provides scientific findings for redesigning the urban environment in related to the urban functional configuration to mitigating the air pollution, ultimately developing sustainable societies.

Highlights

Urban functional fragmentation plays an important role in assessing Nitrogen Dioxide (NO2) emissions and variations
This study explored the impact of urban functional fragmentation on N O2 variations with anthropogenicemission restriction in China
Counterfactual N O2 concentrations during COVID-19 were predicted based on historical NO2 patterns using SARIMAX and were further utilized to quantify the variations comparing with the NO2 in normal days using DTW

Summary

Introduction

Urban functional fragmentation plays an important role in assessing Nitrogen Dioxide (NO2) emissions and variations. Due to the policies of lockdowns and restricted social distancing proposed by the governments, the regular socioeconomic activities are drastically reduced[12], leading to the variation of anthropogenic-generated e missions[13,14,15] These changes have brought opportunities to estimate the impact of urban functional fragmentation under different circumstances of N O2 emissions, i.e. the differences between NO2 emissions before and after lockdowns[16,17]. Li, et al.[23] proposed multiple dimensions including hourly average values, daily average values and the standard deviation of the peak hours to depict the variation of NO2 concentrations Such approach only quantifies the N O2 changes within the research period and cannot evaluate the historical N O2 trends that may be drastically different from the research-period trends caused by unprecedent events, i.e. COVID-19. Venter, et al.[16] defined the N O2 differential as the difference between the N O2 concentration in the research period and the average values of the historical three-year baseline

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