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Analysing and predicting the fine-scale distribution of traffic particulate matter in urban nonmotorized lanes by using wavelet transform and random forest methods

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Abstract

Dynamic traffic and complex roadside environments always cause fine variations in traffic pollutants with many uncertainties in nonmotorized lanes located close to motorways; thus, reliable methods for identifying pollution risks are urgently needed so that measures can be taken to reduce these slow-moving risks. Focusing on the nonmotorized lanes along an expressway in Fuzhou, China, in this study, we established a cycling platform instrumented by portable detectors to collect fine particle (PM2.5), coarse particle (PM10), and black carbon (BC) concentrations at a high spatiotemporal resolution; then, wavelet transform (WT) and random forest (RF) methods were combined to reveal the fine-scale distribution of different particulate matter types. The results indicated that WT was able to accurately decompose the total measurement value (\({C}_{t}\)) of each particulate matter into immediate vehicle-emitted (\({C}_{v}\)) and background-contributed (\({C}_{b}\)) values, thereby successfully identifying the spatiotemporal variations in traffic-induced pollution hotspots rather than background-disguised hotspots. Furthermore, the RF results were substantially better than the land-use regression results with regards to the fine-scale prediction of each particle in nonmotorized lanes. Although the RF predictions of \({C}_{t}\) and \({C}_{v}\) particles differed, traffic pollution hotspots could still be captured by the results. Compared to the measurements, the spatial distributions of the PM2.5 and PM10 predictions presented R2 values larger than 0.96, higher than those of BC (R2 = 0.77); this was the result of the different impacts of the same predictors, especially their differentiated determinants such as barometric pressure, relative humidity and air temperature. This study highlights the potential of using WT and RF methods to reveal fine-scale variations in roadside traffic pollution, which is beneficial for preventing and controlling air pollution in road microenvironments.

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Acknowledgements

We also express appreciation to Xin Chen, Shuting Chen, Fan Ma and Jie Wu from the Traffic Pollution Research Group at the Fujian Agriculture and Forestry University as well as others not mentioned here who provide assistance in this study. Comments and suggestions from the reviewers and editor are highly appreciated.

Funding

This work is supported by the Natural Science Foundation of Fujian Province, China (No. 2021J01105), the National Natural Science Foundation of China (No. 4170155), the Science and Technology Innovation Foundation by Fujian Agriculture and Forestry University (No. KFb22101XA), and the Social Science Foundation of Fujian Province, China (No. FJ2022B065).

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BL: Investigation, methodology, software, validation, visualization, writing—original draft, writing—review and editing; RC: Investigation, software, visualization, writing—original draft, writing—review and editing; WY: Investigation, writing—review and editing; ZW: Conceptualization, data curation, formal analysis, funding acquisition, project administration, resources, supervision, investigation, methodology, writing—original draft, writing—review and editing; XH: Formal analysis, resources, supervision, writing—review and editing; QX, ZF: Formal analysis, resources, writing—review and editing; LZ: Funding acquisition, writing—review and editing.

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Correspondence to Zhanyong Wang.

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Luo, B., Cao, R., Yang, W. et al. Analysing and predicting the fine-scale distribution of traffic particulate matter in urban nonmotorized lanes by using wavelet transform and random forest methods. Stoch Environ Res Risk Assess 37, 2657–2676 (2023). https://doi.org/10.1007/s00477-023-02411-6

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  • DOI: https://doi.org/10.1007/s00477-023-02411-6

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