WORKING PAPER 2023-20 - Real-world NO emissions from ships and implications for future

Calculating NOX emission rates from measurements Based on the sampled concentration of NOX and CO2 in each ship plume, the observed NOX emission rate was calculated by comparing the ratio of NOX to CO2 measured in the plume against background levels, as described by Balzani Lööv et al. [...] The emission rate is calculated by multiplying the observed ratio of NOX to CO2 by the molar mass ratio of NOX to carbon and then by the fuel carbon content (FCC). [...] NOX measured is the X concentration of NOX in the plume and NOX background is the background concentration of NOX. [...] Though mean values indicate compliance with NOX tier limits, results show that 3.5% of Tier I observations are higher than the weighted Tier I limit for all engines sampled, 20.2% of Tier II observations exceed the weighted Tier II limit, and 18.2% of Tier III observations exceed the weighted limit for Tier II, which is the NOX standard they were operating under in the Baltic at the time of observ. [...] To determine how the load distribution in the ECA compares to annual load profiles of the ships, we estimated the engine load distribution of these same ships globally over the full course of 2019 using ICCT’s SAVE model (Olmer et al., 2017) for Tier I and Tier II, as shown by the black lines in Figure 5.