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Professor Junshi XU  許駿什 助理教授

Assistant Professor

Room 10.15

391 03254

junshixu@hku.hk

HKU Scholar Hub
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Junshi Xu is a tenure-track Assistant Professor in the Department of Geography at The University of Hong Kong (HKU). Prior to joining HKU, Professor Xu worked as a Research Associate at the University of Toronto’s Department of Civil & Mineral Engineering, where he earned his Ph.D. in Transportation Engineering in 2020. He also served as the Director of Positive Zero Transport Futures, a living lab initiative evaluating transport decarbonization innovations with positive societal impacts.

At HKU, Professor Xu leads the PEACE (People-oriented, Equitable, Accessible, Community-focused, and Environmental) urban mobility research group, focusing on addressing complex urban transport and environmental challenges. His multidisciplinary research bridges data science, engineering, and social sciences to investigate the interactions between transportation, air quality, climate change, public health, and socioeconomics.

Professor Xu's recent work explores urban air quality and population exposure, particularly concerning emerging and unregulated air pollutants. He leverages machine learning modelling and deep learning applications to investigate environmental justice issues, especially for marginalized individuals facing transport and social challenges. His research aims to achieve thriving, equitable, and sustainable cities through diverse collaborations with academia, government, industry, and communities.

Research Interests

  • Transportation Decarbonization and Air Quality

  • Environmental Monitoring and Population Exposure

  • Machine Learning and Deep Learning Applications in Environmental Science

  • Sustainability, Equity, and Justice in Urban Mobility

  • Urban Transport and City Dynamics

On-going Research Project

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A 60-participant cohort study involving three waves of one-week monitoring among working-age adults living in Sham Shui Po, Central & Western, Kwun Tong, and Tuen Mun.

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A city-wide study aiming to recruit 500 participants to examine environmental stressors and mental health across Hong Kong.

Courses

Profile

GEOG2018

Transport Geography

6

credits

Annual; 2nd Semester

Profile

GEOG2078

Cities and the Urban World: A Global Introduction to Urban Geography

6

credits

Annual; 2nd Semester

Selected Publications

2025

  • Batisse, E., Lloyd, M., Cavanaugh, A., Ganji, A., Xu, J., Hatzopoulou, M.,…Weichenthal, S. (2025). Examining the social distributions in neighbourhood black carbon and ultrafine particles in Montreal and Toronto, Canada. Environment international, 198, 109395. https://doi.org/10.1016/j.envint.2025.109395

  • Ganji, A., Lloyd, M., Xu, J., Weichenthal, S., & Hatzopoulou, M. (2025). Traffic-related air pollution backcasting using convolutional neural network and long short-term memory approach. The Science of the total environment, 976, 179286. https://doi.org/10.1016/j.scitotenv.2025.179286

  • Jaafar, W., Zalzal, J., Xu, J., Ganji, A., & Hatzopoulou, M. (2025). Refining Air Pollution Exposure Estimates: A Comparison of Citywide and Neighborhood Land Use Regression Models in Toronto. Environmental science & technology, 59(35), 18783-18794. https://doi.org/10.1021/acs.est.5c08371

  • Saeedi, M., Xu, J., Ahmed, U., Roorda, M., & Hatzopoulou, M. (2025). Urban Air Pollution Data Collection, Mapping, and Prediction Using Mobile Sensors Installed on Courier Trucks. Transportation Research Record, 2679(7), 236-250. https://doi.org/10.1177/03611981251324208

  • Sun, X., Zou, R., & Xu, J. (2025). Impact of jobs-housing balance on neighborhood traffic and air quality. Urban climate, 60, 102361. https://doi.org/10.1016/j.uclim.2025.102361

  • Wang, K., Li, M., Xu, J., Hatzopoulou, M., & Nurul Habib, K. (2025). Behavioural nudging for greener travel: A discrete choice experiment in the Greater Toronto Area. Energy (Oxford), 322, 135745. https://doi.org/10.1016/j.energy.2025.135745

  • Weichenthal, S., Lavigne, E., Lloyd, M., Venuta, A., Ganji, A., Xu, J.,…Hatzopoulou, M. (2025). Within-city spatiotemporal variations in outdoor ultrafine particles and emergency room visits for cardiovascular outcomes. Environmental epidemiology, 9(5), e419. https://doi.org/10.1097/EE9.0000000000000419

  • Zhang, L., Song, G., Zhang, Z., Zhai, Z., Xu, J., Fan, P., & Ding, Y. (2025). Can Eco-Driving Evaluation Cross Cities? Data Localization and Behavioral Heterogeneity from Beijing to Toronto. Sustainability, 17(9), 3957. https://doi.org/10.3390/su17093957

2024

  • Ganji, A., Saeedi, M., Lloyd, M., Xu, J., Weichenthal, S. and Hatzopoulou, M. (2024). "Air pollution prediction and backcasting through a combination of mobile monitoring and historical on-road traffic emission inventories." Science of The Total Environment 915: 170075. DOI:https://doi.org/10.1016/j.scitotenv.2024.170075

  • Lloyd, M., Olaniyan, T., Ganji, A., Xu, J., Venuta, A., Simon, L., . . . Weichenthal, S. (2024). "Airborne nanoparticle concentrations are associated with brain cancer incidence in Canada’s two largest cities." ISEE Conference Abstracts 2024(1). DOI:https://doi.org/10.1289/isee.2024.0090

  • Lloyd, M., Olaniyan, T., Ganji, A., Xu, J., Venuta, A., Simon, L., . . . Weichenthal, S. (2024). "Airborne Nanoparticle Concentrations Are Associated with Increased Mortality Risk in Canada’s Two Largest Cities." American Journal of Respiratory and Critical Care Medicine 210(11): 1338-1347. DOI:https://doi.org/10.1164/rccm.202311-2013oc

  • Lloyd, M., Olaniyan, T., Ganji, A., Xu, J., Simon, L., Zhang, M., . . . Weichenthal, S. (2024). "Airborne ultrafine particle concentrations and brain cancer incidence in Canada’s two largest cities." Environment International 193: 109088. DOI:https://doi.org/10.1016/j.envint.2024.109088

  • Xu, J., Farrar, E., Jeong, C.-H., Jaafar, W., Anwar, D., Nielsen, I., . . . Hatzopoulou, M. (2024). "Aircraft Activities and Ultrafine Particle Concentrations near a City Airport: Insights from a Measurement Campaign in Toronto, Canada." ACS ES&T Air 1(8): 801-814. DOI:https://doi.org/10.1021/acsestair.3c00114

  • Farrar, E., Kobayaa, N., Jaafar, W., Torbatian, S., Gamage, S. M., Brook, J., . . . Hatzopoulou, M. (2024). "Campus–Community Partnership to Characterize Air Pollution in a Neighborhood Impacted by Major Transportation Infrastructure." ACS ES&T Air 1(12): 1601-1616. DOI:https://doi.org/10.1021/acsestair.4c00155

  • Jaafar, W., Xu, J., Farrar, E., Jeong, C.-H., Ganji, A., Evans, G. and Hatzopoulou, M. (2024). "Challenges and opportunities of low-cost sensors in capturing the impacts of construction activities on neighborhood air quality." Building and Environment 254: 111363. DOI:https://doi.org/10.1016/j.buildenv.2024.111363

  • Xu, J., Saeedi, M., Zalzal, J., Zhang, M., Ganji, A., Mallinen, K., . . . Hatzopoulou, M. (2024). "Exploring the triple burden of social disadvantage, mobility poverty, and exposure to traffic-related air pollution." Science of The Total Environment 920: 170947. DOI:https://doi.org/10.1016/j.scitotenv.2024.170947

  • Weichenthal, S., Lloyd, M., Ganji, A., Simon, L., Xu, J., Venuta, A., . . . Hatzopoulou, M. (2024). "Long-Term Exposure to Outdoor Ultrafine Particles and Black Carbon and Effects on Mortality in Montreal and Toronto, Canada." Res Rep Health Eff Inst 2024(217): 1-63.

  • Venuta, A., Lloyd, M., Ganji, A., Xu, J., Simon, L., Zhang, M., . . . Weichenthal, S. (2024). "Predicting within-city spatiotemporal variations in daily median outdoor ultrafine particle number concentrations and size in Montreal and Toronto, Canada." Environmental Epidemiology 8(4): e323. DOI:https://doi.org/10.1097/ee9.0000000000000323

  • Torbatian, S., Saleh, M., Xu, J., Minet, L., Gamage, S. M., Yazgi, D., . . . Hatzopoulou, M. (2024). "Societal Co-benefits of Zero-Emission Vehicles in the Freight Industry." Environmental Science & Technology 58(18): 7814-7825. DOI:https://doi.org/10.1021/acs.est.3c08867

2023

  • Lloyd, M., A. Ganji, J. Xu, A. Venuta, L. Simon, M. Zhang, M. Saeedi, S. Yamanouchi, J. Apte, K. Hong, M. Hatzopoulou, S. Weichenthal. Predicting spatial variations in annual average outdoor ultrafine particle concentrations in Montreal and Toronto, Canada: Integrating land use regression and deep learning models. 2023. Environment International, 178, 108106. https://doi.org/10.1016/j.envint.2023.108106

  • Ganji, A., O. Youssefi, J. Xu, K. Mallinen, M. Lloyd, A. Wang, A. Bakhtari, S. Weichenthal, M. Hatzopoulou. 2023. Design, calibration, and testing of a mobile sensor system for air pollution and built environment data collection: The Urban Scanner platform. Environmental Pollution, 120720. https://doi.org/10.1016/j.envpol.2022.120720

  • Z. Zhai, J. Xu, M. Zhang, A. Wang, M. Hatzopoulou. Quantifying start emissions and impact of reducing cold and warm starts for gasoline and hybrid vehicles. 2023. Atmospheric Pollution Research, 101646. https://doi.org/10.1016/j.apr.2022.101646

2022

  • Xu, J., M. Zhang, A. Ganji, K. Mallinen, A. Wang, M. Lloyd, A. Venuta, L. Simon, J. Kang, J. Gong, Y. Zamel, S. Weichenthal, M. Hatzopoulou. 2022. Prediction of short-term ultrafine particle exposures using real-time street-level images paired with air quality measurements. Environmental Science & Technology, 56, 12886 - 12897. https://doi.org/10.1021/acs.est.2c03193

  • Ahmed, U., R. Tu, J. Xu, G. Amirjamshidi, M. Hatzopoulou, M. J. Roorda. 2023. GPS-based traffic conditions classification using machine learning approaches. Transportation Research Record, 036119812211113. https://doi.org/10.1177/03611981221111370

  • Zhai Z., J. Xu, G. Song, M. Hatzopoulou. Comparative analysis of drive-cycles, speed limit violations, and emissions in two cities: Toronto and Beijing. 2022. Science of the Total Environment, 811 (x), 152323. https://doi.org/10.1016/j.scitotenv.2021.152323

  • Tu, R., J. Xu, T. Li, H. Chen. 2022. Effective and acceptable eco-driving guidance for human-driving vehicles: a review. International Journal of Environmental Research and Public Health, 19 (12). https://doi.org/10.3390/ijerph19127310

  • Tu, R., J. Xu, A. Wang, M. Zhang, Z. Zhai, M. Hatzopoulou. 2022. Real-world emissions and fuel consumption of gasoline and hybrid light duty vehicles under local and regulatory drive cycles. Science of the Total Environment, 805, 150407. https://doi.org/10.1016/j.scitotenv.2021.150407

  • Wang, A., J. Xu, M. Zhang, Z. Zhai, G. Song, M. Hatzopoulou. 2022. Emissions and fuel consumption of a hybrid electric vehicle in real-world metropolitan traffic conditions. Applied Energy, 306 (PB), 118077. https://doi.org/10.1016/j.apenergy.2021.118077

2021

  • Xu, J., R. Tu, U. Ahmed, G. Amirjamshidi, M. Hatzopoulou, M. J. Roorda. 2021. An eco-score system incorporating driving behavior, vehicle characteristics, and traffic conditions. Transportation Research Part D, 95: 102866. https://doi.org/10.1016/j.trd.2021.102866

  • Wang, A., R. Tu, J. Xu, Z. Zhai, M. Hatzopoulou. 2021. A novel model emission modelling approach and its application with on-road emission measurements. Applied Energy, 306 (PA), 117967. https://doi.org/10.1016/j.apenergy.2021.117967

  • Talaat, H., J. Xu, M. Hatzopoulou, H. Abdelgawad. 2021. Mobile monitoring and spatial prediction of black carbon in Cairo, Egypt. Environmental Monitoring and Assessment, 193 (9). https://doi.org/10.1007/s10661-021-09351-0

  • Wang, A., J. Xu, R. Tu, M. Zhang, M. Adams, M. Hatzopoulou. 2021. Near-road air quality modelling that incorporates input variability and model uncertainty. Environmental Pollution, 284: 117145. DOI: 10.1016/j.envpol.2021.117145

  • Tu, R., J. Xu, A. Wang, Z. Zhai, M. Hatzopoulou. 2021. Effects of ambient temperature and cold starts on excess NOx emissions in a gasoline direct injection vehicle. Science of The Total Environment, 143402. https://doi.org/10.1016/j.scitotenv.2020.143402

2020

  • Xu, J., A. Wang, N. Schmidt, M. Adams, M. Hatzopoulou. 2020. A gradient boost approach for predicting near-road ultrafine particle concentrations using detailed traffic characterization. Environmental Pollution, 265: 114777. https://doi.org/10.1016/j.envpol.2020.114777

  • Xu, J., R. Tu, A. Wang, Z. Zhai, M. Hatzopoulou. 2020. Generation of spikes in ultrafine particle emissions from a gasoline direct injection vehicle during on-road emission tests. Environmental Pollution, 267: 115695. https://doi.org/10.1016/j.envpol.2020.115695

  • Wang, A., J. Xu, R. Tu, M. Saleh, M. Hatzopoulou. 2020. Potential of machine learning for prediction of traffic related air pollution. Transportation Research Part D, 88: 102599. https://doi.org/10.1016/j.trd.2020.102599

  • Zhai, Z., R. Tu, J. Xu, A. Wang, M. Hatzopoulou. 2020. Capturing the variability in instantaneous vehicle emissions based on field test data. Atmosphere (Basel), 11. https://doi.org/10.3390/atmos11070765

  • Xu, J., M. Saleh, M. Hatzopoulou. 2020. A machine learning approach capturing the effects of driving behaviour and driver characteristics on trip-level emissions. Atmospheric Environment, 224: 117311. https://doi.org/10.1016/j.atmosenv.2020.117311

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