After a period of relative stability between 2017 and 2019 (at around 9 µg/m3), the average concentration decreased to 7 µg/m3 in 2020 and 2021 and increased slightly to 8 µg/m3 in 2022.
Ar ôl cyfnod o sefydlogrwydd cymharol rhwng 2017 a 2019 (tua 9 µg/m3), gostyngodd y crynodiad cyfartalog i 7 µg/m3 yn 2020 a 2021 a chynyddodd rywfaint i 8 µg/m3 yn 2022.