Emission dynamics of reactive oxygen species and oxidative potential in particles from a petrol car and wood stove

Abstract. Air pollution is one of the largest environmental health risks and one of the leading causes of adverse health outcomes and mortality worldwide. The possible importance of the oxidative potential (OP) as a metric to quantify particle toxicity in air pollution is increasingly being recognised. In this work, the OP and reactive oxygen species (ROS) activity of particles from fresh and aged petrol passenger car emissions and residential wood combustion (RWC) emissions were investigated using two novel instruments. Applying online instruments using an ascorbic acid (AA) and 2′,7′-dichlorodihydrofluorescein (DCFH) assay provides a much higher temporal resolution compared with traditional filter-based methods and allows for new insights into the highly dynamic changes in the OP and ROS activity of these sources. Due to the efficiency of the particulate filter in the Euro 6d car, almost no primary particles were emitted and, thus, no particle OP or ROS activity was detected in primary exhaust. However, a substantial and highly dynamic OP and ROSs were observed after photochemical ageing due to the formation of secondary particles. Increasing OP and ROS activity due to ageing was also observed when comparing fresh and aged RWC emissions. Overall, RWC emissions had higher OP and ROS signals compared with car emissions. This suggests that aged RWC emissions could be a major contributor to air pollution toxicity and may be an intrinsically more harmful emission source than car exhaust, although the formation potential for secondary particles from car emissions was still high. These measurements illustrate the strong differences and highly dynamic nature of toxicity-relevant particle properties from two air pollution sources and could contribute to more efficient air pollution mitigation policies.