High Time Resolution Quantification of PM2.5 Oxidative Potential in London
STEVEN CAMPBELL, Alexandre Barth, Ian (Gang) Chen, Anja Tremper, Max Priestman, David Ek, Markus Kalberer, David Green, Imperial College London
Abstract Number: 143
Working Group: Health-Related Aerosols
Abstract
Exposure to airborne particulate matter (PM) has been attributed to a wide range of adverse health impacts and millions of premature deaths annually. Despite decades of compelling evidence from epidemiological and laboratory studies, the components of PM responsible for observed health effects remain unclear. Recent studies have widely suggested that oxidative potential (OP), defined as the capability of particles to catalytically produce reactive oxygen species (ROS) with subsequent depletion of antioxidants, is key to determining the health effects of PM exposure. However, accurate quantification of OP has somewhat been hindered by a lack of suitable measurement methods, as many chemical components contributing to OP are short-lived and in low ambient concentrations, posing a significant analytical-chemical challenge.
To overcome this issue, we have developed the online oxidative potential ascorbic acid instrument (OOPAAI), which utilises a direct-to-reagent sampling approach, impinging PM2.5 into an ascorbic acid reagent within seconds, whilst also providing continuous, automated quantification of OP, with a time resolution of 5 minutes.
In this work, the OOPAAI was deployed in a series of ambient measurement campaigns for the first time - in an urban traffic monitoring station, adjacent to a heavily congested arterial route through central London for 3 months during Summer 2023, and at a rural background site for 2 months during Winter 2024. OP was quantified alongside a wide range of established air pollution measurements, including high time resolution elemental PM2.5 composition (XRF, XACT 625i), non-refractory PM (aerosol chemical speciation monitor, ACSM), and black carbon (Aethalometer).
High time resolution measurements reveal the temporal dynamics of OP in London, with changes occurring on timescales of ~hours at the roadside site. This variability in OP was observed at average PM2.5 mass concentrations of 7.1 ± 4.1 µg m-3, below the World Health Organisation interim annual mean target of 10 µg m-3. High time resolution composition measurements and source apportionment analysis reveals transient changes in PM2.5 composition and sources such as break wear, emissions from London underground vents, wood burning, and firework activity are key drivers of OP. Determining the PM composition and sources that drive OP will help synthesise more targeted and effective air pollution mitigation strategies.