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COMMUNICATIONS EARTH & ENVIRONMENT | https://doi.org/10.1038/s43247-023-01050-7 
SO, annual proportional difference (%) 
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Fig. 8 Impact NECA on NO,. Box plot of annual NO, VCD levels between different areas before (BFNC) and after (AFNC) the European NECA entered into 
force in 2021, with minimum, 25% percentile, median, 75% percentile and maximum. 
satellite data clearly reveals visible shipping patterns (Supple- 
mentary Fig. 11). Consequently, it can be stated that emissions 
from OGVs provide the dominant factor in the observed NO, 
VCD data. 
When looking at the average NO, levels before and after the 
implementation of the NECA for the different areas, it was 
demonstrated that NO, levels after the introduction of the NECA 
were impacted in different ways. The BAQPZJR area remained 
ihe most polluted area, with the English Channel following 
closely behind. However, since the implementation of the NECA, 
che Bay of Biscay became the third most polluted area, before the 
Northern NECA. 
Temporal analysis of atmospheric NO; data. For the temporal 
analysis of NO,, an annual and a monthly approach was used. For 
the annual approach, the proportional difference between 2019 
OMMUNICATIONS EARTH & ENVIRONMENT | (2023)4:391 | https: //doi.0rg/10.1038/s43247-023-01050-7 | www.nature.com/commsenv