Maritime shipping is a significant source of anthropogenic emissions, with annual growth of shipping continually on the rise. In the marine environment, shipping emissions often dominate the atmospheric deposition of sulfur and contribute significantly to global sulfur emissions. As a result, the International Maritime Organisation (IMO) introduced a regulation on 01/01/2020 restricting global marine fuel sulfur content from 3.5% to 0.5% w/w. The present study investigated the changes in airmass marine aerosol chemical character arriving at the Penlee Point Atmospheric Observatory (PPAO; 50∘19′ N, 4∘11′ W) to gain insight into the efficacy of the IMO-2020 regulation. The observatory in Southwest England is ideally located next to the port of Plymouth and near to a major international shipping lane in the English Channel with high density marine traffic. Aerosol filter samples were collected from 2020-2021 (n=64). Filter samples were water-leached and subsequent leachates were analysed for major ions using Ion Chromatography, and trace elements using Inductively Coupled Plasma – Mass Spectrometry. Concentrations of V/Ni and calculated non-sea-salt sulfate (nss-SO42-) were compared to PPAO datasets from 2015-16 and 2017-18 respectively. The vanadium/nickel (V/Ni) ratio has been widely used as a marker of shipping emissions in the marine boundary layer, with the range of 2.5 to 4 indicating shipping activity. Trace element analysis showed a drop in V from 2.91 pmol/m3 to 1.44 pmol/m3, and Ni increase from 0.95 pmol/m3 to 4.8 pmol/m3. V/Ni ratio post-IMO-2020 decreased from 3.3 to 0.28, showing a significant change to the trace metal signature of marine aerosols. Post-IMO-2020 nss-SO42- concentrations were significantly lower than pre-IMO-2020 values (n=109, p<0.05), with total nss-SO42- concentration dropping from 1.35 µg/m3 to 0.33 µg/m3. A change from nss-SO42- dominated atmospheric sulfur pre-IMO-2020 to primarily natural dimethylsulfide dominated sulfur was observed. Clear seasonal nss-SO42- fluctuations increasing during spring and summer were visible post-IMO-2020. These results indicate a major change to the atmospheric chemistry of sulfur in the lower atmosphere near to regions of intense shipping.

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