Articles | Volume 17, issue 12
Research article
28 Jun 2017
Research article |  | 28 Jun 2017

Enhanced toxicity of aerosol in fog conditions in the Po Valley, Italy

Stefano Decesari, Mohammad Hossein Sowlat, Sina Hasheminassab, Silvia Sandrini, Stefania Gilardoni, Maria Cristina Facchini, Sandro Fuzzi, and Constantinos Sioutas

Abstract. While numerous studies have demonstrated the association between outdoor exposure to atmospheric particulate matter (PM) and adverse health effects, the actual chemical species responsible for PM toxicological properties remain a subject of investigation. We provide here reactive oxygen species (ROS) activity data for PM samples collected at a rural site in the Po Valley, Italy, during the fog season (i.e., November–March). We show that the intrinsic ROS activity of Po Valley PM, which is mainly composed of biomass burning and secondary aerosols, is comparable to that of traffic-related particles in urban areas. The airborne concentration of PM components responsible for the ROS activity decreases in fog conditions, when water-soluble species are scavenged within the droplets. Due to this partitioning effect of fog, the measured ROS activity of fog water was contributed mainly by water-soluble organic carbon (WSOC) and secondary inorganic ions rather than by transition metals. We found that the intrinsic ROS activity of fog droplets is even greater (> 2.5 times) than that of the PM on which droplets are formed, indicating that redox-active compounds are not only scavenged from the particulate phase, but are also produced within the droplets. Therefore, even if fog formation exerts a scavenging effect on PM mass and redox-active compounds, the aqueous-phase formation of reactive secondary organic compounds can eventually enhance ROS activity of PM when fog evaporates. These findings, based on a case study during a field campaign in November 2015, indicate that a significant portion of airborne toxicity in the Po Valley is largely produced by environmental conditions (fog formation and fog processing) and not simply by the emission and transport of pollutants.

Short summary
Exposure to atmospheric particulate matter (PM) represents one of the biggest environmental health risks. We show that the intrinsic PM toxicity at a rural site, far from traffic emissions, is comparable to that of urban areas heavily impacted by traffic. Potentially toxic, redox-active compounds in PM are efficiently scavenged in the presence of fog but are also produced in fog. These findings provide evidence that atmospheric processing can significantly alter the toxicity of airborne PM.
Final-revised paper