Applicability of Compact Low- and Mid-Cost Sensors to Monitor Air Pollutant Emissions from Inland Ships

Abstract Inland ships emit relevant quantities of air pollutants, including nitrogen oxides, particulate matter, ultrafine particles and black carbon. However, onshore measurements of ship exhaust emissions under real-driving conditions are rare due to the high cost of specialized instrumentation and the effort for setup, operation and maintenance. Using compact and flexible low- and mid-cost air pollutant sensors can increase the spatial coverage of these measurements in monitoring activities. This offers a broader and more representative overview of the dispersion of ship emissions in densely populated areas, enabling a better quantification of their impact on local air quality. We investigated the suitability of various particle and gas sensors by conducting co-located onshore measurements alongside reference instruments on the banks of the river Rhine in Germany over the course of one year. We identified suitable sensors that met specific criteria, such as having a sufficiently low instrumental noise level, a good correlation with the reference instrument, and a fast response time. These criteria are essential for analysing the rapidly changing concentrations observed in ship plumes, as well as for meeting requirements that fundamentally differ from those involved in investigating urban air pollution. Applicable sensors include the mid-cost black carbon sensor MA350 (slope of 0.77 and R² = 0.95 when compared with the reference instrument), the mid-cost ultrafine particle sensor Partector 2 Pro (R² = 0.85) as well as the low-cost carbon dioxide sensor K30 FR (R² = 0.98), and the nitrogen monoxide (R² = 0.99) and nitrogen dioxide (R² = 0.81) sensors from Alphasense. Although the selected sensors were generally suitable for measuring ship exhaust emissions onshore, the elevated noise level of these sensors and the challenging correction of the temperature dependence of the electrochemical sensors reduced the number of analysable ship peaks.