Do we need high temporal resolution modelling of exposure in urban areas? A test case

H Woodward; A Schroeder; A de Nazelle; C C Pain; M E J Stettler; H ApSimon; A Robins; P F Linden

doi:10.1016/j.scitotenv.2023.163711

Do we need high temporal resolution modelling of exposure in urban areas? A test case

Sci Total Environ. 2023 Aug 10:885:163711. doi: 10.1016/j.scitotenv.2023.163711. Epub 2023 May 4.

Authors

H Woodward¹, A Schroeder², A de Nazelle³, C C Pain⁴, M E J Stettler⁵, H ApSimon³, A Robins⁶, P F Linden⁷

Affiliations

¹ Centre for Environmental Policy, Imperial College London, London, UK. Electronic address: huw.woodward@imperial.ac.uk.
² MRC Epidemiology Unit, University of Cambridge School of Clinical Medicine, Clifford Allbutt Building, Cambridge Biomedical Campus, Cambridge, UK.
³ Centre for Environmental Policy, Imperial College London, London, UK.
⁴ Department of Earth Science and Engineering, Imperial College London, London, UK.
⁵ Centre for Transport Studies, Faculty of Engineering, Department of Civil and Environmental Engineering, Imperial College London, London, UK.
⁶ Department of Mechanical Engineering Sciences, University of Surrey, Guildford, UK.
⁷ Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge, UK.

PMID: 37149198
DOI: 10.1016/j.scitotenv.2023.163711

Abstract

Roadside concentrations of harmful pollutants such as NO_x are highly variable in both space and time. This is rarely considered when assessing pedestrian and cyclist exposures. We aim to fully describe the spatio-temporal variability of exposures of pedestrians and cyclists travelling along a road at high resolution. We evaluate the value added of high spatio-temporal resolution compared to high spatial resolution only. We also compare high resolution vehicle emissions modelling to using a constant volume source. We highlight conditions of peak exposures, and discuss implications for health impact assessments. Using the large eddy simulation code Fluidity we simulate NO_x concentrations at a resolution of 2 m and 1 s along a 350 m road segment in a complex real-world street geometry including an intersection and bus stops. We then simulate pedestrian and cyclist journeys for different routes and departure times. For the high spatio-temporal method, the standard deviation in 1 s concentration experienced by pedestrians (50.9 μg.m^-3) is nearly three times greater than that predicted by the high-spatial only (17.5 μg.m^-3) or constant volume source (17.6 μg.m^-3) methods. This exposure is characterised by low concentrations punctuated by short duration, peak exposures which elevate the mean exposure and are not captured by the other two methods. We also find that the mean exposure of cyclists on the road (31.8 μg.m^-3) is significantly greater than that of cyclists on a roadside path (25.6 μg.m^-3) and that of pedestrians on a sidewalk (17.6 μg.m^-3). We conclude that ignoring high resolution temporal air pollution variability experienced at the breathing time scale can lead to a mischaracterization of pedestrian and cyclist exposures, and therefore also potentially the harm caused. High resolution methods reveal that peaks, and hence mean exposures, can be meaningfully reduced by avoiding hyper-local hotspots such as bus stops and junctions.

Keywords: Air pollution; Exposure; High resolution; Modelling; NOx; Road transport.

MeSH terms

Air Pollutants* / analysis
Air Pollution* / analysis
Environmental Monitoring / methods
Environmental Pollutants*
Particulate Matter / analysis
Vehicle Emissions / analysis

Substances

Air Pollutants
Vehicle Emissions
Environmental Pollutants
Particulate Matter