This study examines the relationship between short-run variation in vessel activity and coastal air quality in a major coastal city. Hourly monitor-level air-quality readings in Busan, South Korea are linked to a port-exposure index that aggregates hourly vessel tonnage at piers using inverse-distance weights. Panel regressions with fixed effects suggest a positive relationship between port exposure and PM10 and PM2.5. A back-of-the-envelope calculation implies that a 1,000-unit increase in the exposure index corresponds to about 0.18% higher PM10 and 0.33% higher PM2.5. The estimates provide an exposure-concentration mapping that may serve as a basis for further study into port-related environmental impacts in coastal cities.