Impact of Shipping Emission Regulations on Atmospheric Vanadium Along U.S. North Atlantic Coast and Over the Western North Atlantic Ocean

Ship emissions from high sulfur residual fuel oil (RFO) are a major source of air pollution in coastal and marine environments. Emissions include sulfur oxides as well as vanadium (V) and nickel (Ni) enriched fine particulate matter (PM2.5) . Near coasts, the International Maritime Organization (IMO) has implemented Sulfur Emission Control Areas where ships have to operate on low sulfur marine fuel. In this study, we integrate 15 years of chemically speciated PM2.5 data collected at IMPROVE sites along the U.S. east coast with in-cloud observations from the 2020-2022 NASA ACTIVATE flight campaign over the northwest Atlantic to assess the impact of maritime regulations on ambient vanadium concentrations. We find statistically significant reductions in coastal atmospheric vanadium (~ 80% - 89%) after IMO regulations implementation. Reductions in particulate nickel (67% - 79%) and sulfate (53% - 59%) levels are also observed. While the V/Ni ratio is traditionally used as tracer for RFO-operated marine engines, we show measurements in shipping lanes comparable to those in areas not affected by shipping emissions. This means that V/Ni is no longer a reliable marker for detecting plume exhaust from ships running on low-sulfur fuel, while vanadium alone represents a stronger tracer. Under a low-sulfur fuel regime, cloud water vanadium concentrations over the northwest Atlantic are an order of magnitude lower than in PM2.5 at coastal sites. Vanadium
concentrations above 75th percentile were observed in cloud droplets enriched in nss-sulfate and nitrate suggesting a potential role of ship-emitted vanadium in catalyzing in-cloud oxidation reactions.