Influence of ship emissions on PM_2.5 in Shanghai: From COVID19 to OMICRON22 lockdown episodes

Air quality has improved significantly in the recent 10 years, but there is still a wide gap compared to the WHO AQG level. The concentration of PM_2.5 during OMICRON in 2022 was 21.7 μg m⁻³, which marked the lowest historical record under the lockdown status of the whole urban area, still exceeding the national Level 1 standard. PMF results have shown that the contributions of ship emissions increased from 2020 to 2022 during the historical OMICRON episodes, with growth rates of 9.7% and 10.7%, respectively. AIS data indicated an overall increase in shipping activities around Shanghai during the OMICRON22-2021 period. The strict control of urban activities during the silent period in 2022 reduced ship activities by 21.0% and 31.8% in the ChongMingMsa and WuSongMsa ranges close to Shanghai, respectively. However, significant growth was observed in the sea regions of ShanghaiMsa and ZhouShan-NingBoMsa, with growth rates of 44.2% and 33.7%, respectively. The total number of anchored ships in the sea region of YangShanGangMsa increased by 56.7%. CWT analysis indicated that the lockdown measures only changed the distributions of the ship emissions. More forceful measures for the reductions of the ship emissions should be considered.