Surface monitoring underestimates air-pollution burden of a major Global South port

Maritime ports are major sources of urban air pollution, but surface monitoring often fails to capture pollution at higher levels from ship exhaust stacks and coastal atmospheric processes, a gap especially important for Global South ports. Here we conducted a height-resolved assessment at the Port of Paranaguá in Brazil during the southern hemisphere spring. Using multi-height measurements combined with meteorological analysis and a space-and-time-stratified case-crossover approach, we identified strong vertical differences in pollutant concentrations. Sulfur dioxide was consistently elevated at heights corresponding to ship exhaust, indicating interception of ship plumes. Nitrogen dioxide showed a weaker but consistent increase at mid-levels, influenced by port activity and atmospheric mixing. Fine particulate matter showed modest enhancement aloft, while the strongest operation-related episodes occurred near the surface. Pollution risk increased substantially during port operations, rising by up to 74% during cargo handling. These findings show that surface-only monitoring fails to capture the full extent of exposure-relevant pollution in port environments. Air pollution in a major Brazilian port is strongly elevated above the surface and intensifies during port operations, which surface monitoring misses, based on multi-height air measurements combined with meteorology and a case crossover analysis during spring.