Emissions of NOx, SO2, CO, and HCHO from commercial marine shipping during Texas Air Quality Study (TexAQS) 2006

We report measurements of NOx, SO2, CO, and HCHO mass‐based emission factors from more than 200 commercial vessel encounters in the Gulf of Mexico and the Houston‐Galveston region of Texas during August and September, 2006. For underway ships, bulk freight carriers have the highest average NOx emissions at ∼87 g NOx (kg fuel)−1, followed by tanker ships at ∼79 g NOx (kg fuel)−1, while container carriers, passenger ships, and tugs all emit an average of about ∼60 g NOx (kg fuel)−1. Emission of NOx from stationary vessels was lower, except for container ships and tugs, and likely reflects use of medium‐speed diesel engines. Overall, our mean NOx emission factors are 10–15% lower than published data. Average emission of SO2 was lower for passenger ships and tugs and tows (6–7 g SO2 (kg fuel)−1) than for larger cargo vessels (20–30 g SO2 (kg fuel)−1). Our data for large cargo ships in this region indicate an average residual fuel sulfur content of ∼1.4% which is a factor of two lower than the global average of 2.7%. Emission of CO was low for all categories (7–16 g CO (kg fuel)−1), although our mean overall CO emission factor is about 10% higher than published data. Emission of HCHO was less than 5% that of CO. Despite considerable variability, no functional relationships, such as emissions changes with engine speed or load, could be discerned. Comparison of emission factors from ships to those from other sources suggests ship emissions in this region cannot be ignored.