Atmospheric particulate matter (PM), a public health concern worldwide, is at present regulated according to its mass concentration1. However, it is increasingly thought that mass concentration may not fully capture the physicochemical properties of PM linked to its health impact2. Consequently, it has been suggested to further investigate the adequacy of this metric as an unequivocal indicator of PM health effects3–5. The new European regulation on air quality introduced oxidative potential (OP) as a recommended parameter to be monitored at supersites1, to explore further deciphering information about PM reactivity and health impacts6,7. Here we use a database of almost 11,500 OP measurements from 43 locations across parts of Europe that were analysed with the two most commonly used OP assays8, OPAA and OPDTT, with a standardized protocol9,10. We find high spatial variability of OP across Europe, strongly influenced by site type, such as urban or rural. Accounting for OP alongside PM mass suggests that further improvements in urban air quality may require consideration, particularly near roads, where volumetric OP of PM10 exceeds background levels by a factor of 2.4 to 3.1, depending on the assay used. Analysis of mitigation strategies shows that traffic is a key source to target for effectively reducing OP in cities, whereas comprehensive reductions in PM from both traffic and biomass burning are required to also meet World Health Organization mass guidelines. Although the epidemiological evidence for OP health impacts is still evolving2,8, our findings may help inform the interpretation of future work.
