Evolution of the V/Ni Ratio in Response to IMO Regulation-Induced Fuel Shifts and Scrubber Use

The vanadium/nickel (V/Ni) ratio has long served as a chemical fingerprint of shipping emissions, typically exhibiting values around 3. Also, over the past two decades, the progressive implementation of the International Maritime Organization (IMO) fuel sulfur content (FSC) regulations has driven major shifts in both fuel characteristics and compliance technologies. The widespread adoption of desulfurized marine fuels has markedly decreased average V/Ni ratios in coastal environments (to ∼1), whereas the continued use of heavy fuel oil (HFO) with exhaust gas cleaning systems (scrubbers) appears to maintain pre-IMO values. Compiling two decades of V/Ni data from ship emission studies, this work assesses temporal and technological trends to evaluate the robustness of this ratio as a diagnostic marker. The results show a global decrease in V/Ni ratios driven by fuel desulfurization with residual variability reflecting fuel type, sampling context, and industrial influence. Overall, the V/Ni ratio is a relevant tracer of shipping emissions in coastal areas and a potential indicator of scrubber operation in an evolving regulatory landscape.