Impact of SO2 Emission Controls on Water-Soluble Iron in Fine Particulate Matter Air Pollution in Atlantic Canada

Human exposure to fine particulate matter (PM2.5) pollution is linked to acute and chronic cardiovascular, pulmonary diseases, with numerous epidemiological and toxicological studies demonstrating that water-soluble iron (WS-Fe) in PM2.5 is an important contributor to these adverse health effects. Although the predominant source of Fe from mineral dust is initially emitted in an insoluble form at the time of emission, Fe solubility measured in ambient PM2.5 is greater, indicating the contribution of unknown WS-Fe primary and secondary sources (i.e., atmospheric chemical processing resulting in the iron dissolution). While studies have shown that proton-mediated and ligand-mediated reactions convert insoluble Fe into a soluble form during atmospheric transport in Ontario, the factors controlling WS-Fe in Atlantic Canada (Saint John, New Brunswick and Halifax, Nova Scotia) remain unclear. In addition, since Saint John and Halifax are both known as ports in Atlantic Canada, emissions of sulfur dioxide from large marine vessels can potentially influence WS-Fe production, as sulfur dioxide affects aerosol pH conditions by forming sulfuric acid that affects iron dissolution. Therefore, the impact of implementing the SO2 emission controls, including North American Emission Control Area (NAECA) low-sulfur fuel regulations and Nova Scotia annual SO2 emission caps under the Air Quality Regulations on WS-Fe in Atlantic Canada is explored in this study. Results demonstrate that the implementation of low-sulfur fuel regulations has led to a reduction in WS-Fe: (1) directly, by decreasing primary emissions of WS-Fe from ships, and (2) indirectly, by a potential reduction in sulfur dioxide emission, which influences aerosol pH and consequently, secondary production of WS-Fe through atmospheric processing of iron-containing aerosols.