02 May 2023
 | 02 May 2023
Status: this preprint is currently under review for the journal ACP.

Impacts of maritime shipping on air pollution along the U.S. East Coast

Maryam Golbazi and Cristina Archer

Abstract. Air pollution is considered a leading threat to human health in the United States (U.S.) and worldwide. An important source of air pollution in coastal areas is the globally increasing maritime shipping traffic. In this study, we take a high-resolution modeling approach to investigate the impacts of ship emissions on concentrations of various atmospheric pollutants, under the meteorological conditions and emissions of the year 2018. We utilize the Comprehensive Air Quality Model with extensions (CAMx) to simulate transport, diffusion, and chemical reactions, and the Weather Research and Forecasting (WRF) model to provide the meteorological inputs. We focus on four criteria pollutants – fine particulate matter with a diameter smaller than 2.5 μm (PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2), and ozone (O3) – as well as nitrogen oxide (NO), and we calculate their concentrations in the presence and absence of the ship emissions along the U.S. East Coast, particularly in the proximity of major ports.

We find that ship emissions increase the PM2.5 concentrations over the ocean and sparse areas inland. The 98-th percentile of the 24-hour average PM2.5 concentrations (the "design value'' used by the U.S. Environmental Protection Agency) increased by up to 3.2 μm m−3 in some coastal areas. In addition, ships contribute significantly to SO2 concentrations, up to 95 % over the Atlantic and up to 90 % over land in coastal states, which represents a ~45 ppb increase in the SO2 design values in some states. The 98-th percentile of the hourly NO2 concentrations also increased by up to 15 ppb at the major ports and along the shore. In addition, we find that the impact of shipping emissions on O3 concentrations is not uniform, meaning that ships affect ozone pollution in both positive and negative ways. Over the ocean, O3 concentrations were significantly higher in the presence of ships, but in major coastal cities, O3 concentrations decreased in the presence of ships. Our simulation results show that ships emit significant amounts of fresh NO in the atmosphere, which then helps scavenge O3 in VOC-limited areas, such as major ports. By contrast, over the ocean (NOx-limited regime), enhanced NOx (NO2 + NO) concentrations due to ships contribute to the formation of O3 and therefore enhance O3 concentrations. Overall, due to the dominant southwesterly wind direction in the region, the impacts of ships on air pollutants mainly remain offshore. However, in coastal states near major ports, the impacts are significantly important.

Maryam Golbazi and Cristina Archer

Status: open (until 22 Jun 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Maryam Golbazi and Cristina Archer

Maryam Golbazi and Cristina Archer


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Short summary
We use scientific models to simulate the effects of the ships on air quality along the east coast of the USA. We find an increase in three major pollutants in coastal areas. We also find a decrease in ground-level ozone in large coastal cities. This is because ships produce high levels of nitrogen oxides, another harmful pollutant, which negatively interact with ozone in highly polluted urban areas. Overall, due to the dominant wind direction, the majority of air pollution remains offshore.