Implications of the Improvement in Atmospheric Fine Particles: A Case Study of COVID-19 Pandemic in Northern Taiwan

The outbreak of COVID-19 pandemic in northern Taiwan led to the implementation Level 3 alert measures during 2021 and thereby impacted air quality significantly, which provided an unprecedented opportunity better understand control strategies on pollutants future. This study investigated variations sources, chemical characteristics human health risks PM2.5 comprehensively. mass concentrations decreased from pre-alert by 49.4%, inorganic ions, i.e., NH4+, NO3- SO42-, dropped even more 71%, 90% 52%, respectively. Nonetheless, organic matter (OM) elemental carbon (EC) simply 36% 13%, caused composition change so that carbonaceous dominated instead ions. Correlation-based hierarchical clustering analysis further showed was clustered with alert, while ions both post-alert periods. Moreover, 6 sources were identified positive matrix factorization (PMF), secondary nitrate (i.e., aging traffic aerosols) exhibited most significant decrease yet primary traffic-related emissions, matter, changed insignificantly. implied aerosols could be easily controlled when volume declined, source needs efforts future, especially for reduction matter. Therefore, cleaner energy vehicles is still needed. Assessments carcinogenic risk non-carcinogenic induced trace elements insignificant decrease, can attributed factories did not shut down alert. serves as a metric underpin mitigation pollution future highlights importance PM2.5.