Abstract
This research quantifies current sources of non-exhaust particulate matter traffic emissions in London using simultaneous, highly time-resolved, atmospheric particulate matter mass and chemical composition measurements. The measurement campaign ran at Marylebone Road (roadside) and Honor Oak Park (background) urban monitoring sites over a 12-month period between 1 September 2019 and 31 August 2020. The measurement data were used to determine the traffic increment (roadside–background) and covered a range of meteorological conditions, seasons, and driving styles, as well as the influence of the COVID-19 “lockdown” on non-exhaust concentrations. Non-exhaust particulate matter (PM)10 concentrations were calculated using chemical tracer scaling factors for brake wear (barium), tyre wear (zinc), and resuspension (silicon) and as average vehicle fleet non-exhaust emission factors, using a CO2 “dilution approach”. The effect of lockdown, which saw a 32% reduction in traffic volume and a 15% increase in average speed on Marylebone Road, resulted in lower PM10 and PM2.5 traffic increments and brake wear concentrations but similar tyre and resuspension concentrations, confirming that factors that determine non-exhaust emissions are complex. Brake wear was found to be the highest average non-exhaust emission source. In addition, results indicate that non-exhaust emission factors were dependent upon speed and road surface wetness conditions. Further statistical analysis incorporating a wider variability in vehicle mix, speeds, and meteorological conditions, as well as advanced source apportionment of the PM measurement data, were undertaken to enhance our understanding of these important vehicle sources.
Highlights
Clean air is important for human health and the environment [1,2]
A 12-month measurement campaign was undertaken at Marylebone Road and Honor Oak Park to quantify non-exhaust emissions using highly time-resolved PM10 and elemental composition measurements
To determine the non-exhaust emission concentrations, previously developed scaling factors were applied to the measured concentrations of Ba, Zn, and Si, respectively
Summary
Clean air is important for human health and the environment [1,2]. Significant reductions in particulate matter (PM) exhaust emissions have occurred as a result of the adoption of diesel vehicle particulate filters, whilst gasoline particulate filters are expected to mitigate PM emissions from the uptake of gasoline direct injection technology [3,4]. Laboratory studies have assessed specific non-exhaust emission components under drive cycles which represent real-world driving conditions, simulating reproducible investigations in confined and controlled test conditions [15,16,17,18,19,20] These studies included the assessment of important variables such as material type and composition, vehicle speed, and temperature (ambient and component), to determine brake and tyre particle number and mass emissions [15,16,17,18,19,20]. To quantify real-world non-exhaust emissions in London, this study utilised simultaneous, highly time-resolved atmospheric PM mass and elemental composition measurements at roadside and background locations over a 12-month period to identify the increment in concentrations attributable to the vehicle fleet. The mean of these two sites was used to represent background CO2 concentrations to improve temporal coverage for the dilution approach
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