We use scientific models to study the impact of ship emissions on air quality along the US East Coast. We find an increase in three major pollutants (PM_2.5, NO₂, and SO₂) in coastal regions. However, we detect a reduction in ozone (O₃) levels in major coastal cities. This reduction is linked to the significant emissions of nitrogen oxides (NO_x) from ships, which scavenged O₃, especially in highly polluted urban areas experiencing an NO_x-limited regime.