Ocean-going ships are mostly driven by high‑sulfur heavy fuel oil, which poses public health and environmental concerns. Emission control areas (ECA) have been developed for the regulatory control of the sulfur content in fuel. We tracked 28 sample vessels that entered and exited Shanghai Port, to understand how air pollutants, including oxysulfides (SOx), nitric oxide (NOx), and particulate matter smaller than 10 μm (PM10), would change under the ECA regulations. Emission reductions vary with the types and sizes of the ships. In our sample pool, oil/chemical tankers and container ships have the highest decline rates of SOx emissions at 26.8%–56.4% and 17.4%–56.6%, respectively. Cruise ships, container ships, and liquefied gas carriers occupy the highest share ratios of pollutant emissions in the sample pool because of the higher average gross tonnage and correspondingly higher-rated power of the ships' main engines. As expected, SOx and PM10 emissions under hoteling conditions (operations while stationary at dock) can be considerably reduced by switching to low-sulfur fuel. Using fuel with the much lower sulfur content of 0.1% m/m in the ECA, the SOx and PM10 emissions of our sample pool could be reduced considerably by up to 94.4% and 78.3%, respectively, compared to the 0.5% m/m sulfur content used during ship hoteling. •Emission control areas (ECA) have been developed for regulatory control of sulfur content in fuel.•We tracked 28 vessels to understand how air pollutants would change under the ECA regulations.•Emission reductions vary with the types and sizes of the ships.•Oil/chemical tankers and container ships have the highest decline rates of SOx emissions.•Oxysulfides and particulate matter emissions under hoteling conditions can be considerably reduced with lower sulfur fuel.•ECA regulations are effective and more coastal nations should consider implement a similar scheme.