A Source Focused Approach Applied to Urban Mobile Measurements

Mobile measurements have emerged as a powerful tool for characterising air pollutant sources, providing high-resolution spatial and temporal information that complements fixed monitoring stations. In this study, we used mobile measurements to investigate air pollution across York, England. High time resolution measurements were made of nitrogen oxides (NOx), carbon dioxide (CO2), methane (CH4), fine particulate matter (PM2.5) and over 20 individual volatile organic compounds (VOCs). The measurements were made on a pre-defined route and repeated 19 times across different times of the day, days of the week, and seasons. The measurement route covered the densely populated city centre, characterised by heavy traffic and numerous commercial activities, such as restaurants and beauty salons, and extended to the outskirts dominated by agricultural land and green spaces. This spatial coverage allows the investigation of contrasting local emission sources, including poorly quantified source types such as restaurants and traffic-related emissions, as well as background pollutant concentrations affected by regional source contributions. Our study explores how best to partition the measurements into background and local increments to investigate the nature of the sources affecting measurements across the city. We also explore the potential of using information on individual source locations for sectors such as restaurants as a method to examine the relationship between source density and pollutant concentration. We derive the source factor through advanced Gaussian modelling of individual sources based on their location and local meteorology. The results demonstrate the applicability of mobile measurements combined with the source factor method for resolving fine-scale variability in urban air pollution.