In October 2022, the European Commission published a proposal for a revision of the Ambient Air Quality Directive, introducing stricter thresholds for pollution, more closely aligned with new limits set by the WHO, and strengthening rules for air quality monitoring to support preventive action and targeted measures. One of the latter is the monitoring of the Reactive Oxygen Species (ROS) contained in ambient aerosol. Although a direct mechanism linking PM exposure to health outcomes has not yet been well established, it is believed that ROS (redox-active components, like metals and several organic species), present in polluted air or generated from photochemical reactions, can induce oxidative stress in the human organism. During an intensive measurement campaign, daytime and nighttime PM_2.5 samples were collected at the urban environment of Ioannina, a rural mountainous moderately inhabited city (~0.15M inhabitants), impacted by intense residential wood burning (RWB) for heating purposes especially during winter nighttime, that in combination with its topography, results in a magnified accumulation of atmospheric pollutants. The oxidative potential of the collected samples was determined using a semi-automated system, applying the dithiothreitol (DTT) assay. It is worth noting that nighttime DTT values were three times higher than the daytime ones, highlighting the critical role of RWB in population exposure. Furthermore, the measured OP levels were compared with carcinogenic markers such as polycyclic aromatic hydrocarbons (PAHs) and their oxygenated derivatives (OPAHs). All the aforementioned levels were also compared to the respective values from Athens, the capital of Greece with almost 4 million inhabitants, and from Heraklion, an urban center in Crete, with 0.2M inhabitants. The results elucidate the importance of regional aerosol transportation during the warmest period of the year, and the dominant impact of local sources in wintertime.