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

Abstract

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.

Urban Heat Island Over Delhi Punches Holes in Widespread Fog in the Indo‐Gangetic Plains

“…The central valley fog is a persistent low-cloud feature observed in late autumn-winter months (Baldocchi & Waller, 2014;Herckes et al, 2015). Similar observations are seen over the Po valley, a low-lying extensive basin south of the Alps, where winter fog and pollution haze is frequently observed across the basin (Decesari et al, 2017;Giulianelli et al, 2014), with fog holes evident over urban/industrial cities (e.g., Milan).…”

“…Owing to its rich hydrological resources and agriculture, the IGP is among the most densely populated regions with over 900 million inhabitants. The fog period coincides with the severe anthropogenic winter haze in south and east Asia as well as elevated winter time pollution levels in the Po valley and California's central valley, with significant degradation to air quality (Decesari et al, 2017;Herckes et al, 2015;Sun et al, 2006;Wang et al, 2016). Polluted fog is widely known to affect public health (Stone, 2002).…”

Local Arctic Air Pollution: A Neglected but Serious Problem

“…In fact, recent investigations of the toxicology of PM-in form of reactive oxygen species (ROS) present in the aerosol particleshave shown that ROS can be produced in fog droplets. Hence, the fog-processed PM can be more harmful to health (Decesari et al, 2017).…”

“…Health effects research has primarily focused on contaminants such as polycyclic aromatic hydrocarbons, persistent organic pollutants, heavy metals, and mercury, rather than the most abundant air pollutants. Further, there is evidence that fog processes PM contains more reactive oxygen species (Decesari et al, 2017) and is hence more toxic. There is also a clear bias toward air pollution information in larger Arctic cities.…”

Fogs: Physical Basis, Characteristic Properties, and Impacts on the Environment and Human Health

“…Bourcier et al [33] have provided experimental evidence of biomass burning as a source of atmospheric 137 Cs present in cloud water. Fog droplets capturing radio-nuclides could either prolong or shorten the residence time of the radioactive atmospheric pollutants, by preventing fast deposition or enhancing it by scavenging [34]. Thus, fogs can play an important role in spreading, keeping close to the surface, and in wet deposition of radioactive particles, with direct impacts on the human health and ecosystems.…”