Multi‐year variations of submicron aerosol composition and sources in Ireland

The air quality in Ireland was once significantly deteriorated by air pollutants emitted from domestic coal combustion activities in the 1980s. Thanks to the smoky coal ban which was put into force in 1990, the air pollution in Ireland has been improved gradually and surely. However, extreme air pollutions with the mass concentration of submicron aerosols (PM₁) exceeding 300 μg m^-3 were still observed sporadically during cold months, which were mainly related to domestic solid fuel combustion, and the disproportionate impacts from so-called “low-carbon” and “carbon-neutral” solid fuels (e.g., peat and wood). Moreover, due to the increasing wood stove advertisements and significant fuel price increase caused by Ukrainian-Russian war, the emissions from local solid fuel combustion activities could greatly impair the air quality in Ireland in the future. Since the situation is changing year to year, it’s very critical to conduct continuous field aerosol measurements and have a deeper insight into the medium/long-term variations for more targeted and effective regulations in the future. In this study, based on the parallel real-time measurements of submicron aerosol species at three representative sites over Ireland, the multi-year variations of aerosol chemical composition and source emissions have been analyzed.

The air quality in Dublin has been improved gradually since 2016, with the annual average mass concentration of PM₁ decreased from 8.0 μg m^-3 in 2016 to 4.1 μg m^-3  in 2022, and the total number of days when PM₁ concentration exceeds the WHO recommendation value (15 μg m^-3) has decreased to 11 days in 2022. Specifically, the extreme air pollutions have been reduced significantly, e.g., the maximum hourly PM₁ concentration has decreased to 77 μg m^-3 in 2022 compared to 317 μg m^-3 in 2016.  The high PM₁ concentrations in Dublin were more related to local emissions, especially domestic solid fuel burning, characterized by large contributions from primary organic aerosols. While long-range transport also plays an important role with high fractions of inorganics especially Nitrate (NO₃). The chemical composition of PM₁ in Dublin was similar over the years, i.e., dominated by Organics (Org) and then followed by NO₃ or sulfate (SO₄). However, it’s worrisome to find that the mass concentration of SO₄ has been increasing since 2021 and showed higher contribution to PM₁ especially during cold months, indicating that the sharply increasing fuel prices recently may have led to a change in fuel usage, possibly with more coal and solid fuel combustion in households. This could indicate severe air pollution episodes that need further and more effective regulations in the near future to ensure good enough air quality.