Comparison of pollution characteristics and magnetic response of heavy metals in dustfall before and after COVID-19 outbreak in Shanghai

In this study, dustfall samples were systematically collected in various regions of Shanghai before and after the occurrence of COVID-19 in December 2019 and December 2020. The magnetic response, content and pollution status of relevant heavy metal elements in the samples were analyzed using environmental magnetism, geochemistry, scanning electron microscopy (SEM) and the enrichment factor (EF) method. The results show that the magnetic particles in the dustfall samples are mainly pseudo-single-domain (PSD) and multi-domain (MD) ferrimagnetic minerals, and Fe, Zn, Cr, and Cu are mainly concentrated in the districts with intensive human activities. Due to restrictions on human activities following the COVID-19 epidemic, both the values of magnetic parameters and the heavy metal pollution level in 2019 are more significant than those in 2020, which is consistent with the Air Quality Index (AQI) results. In addition, magnetic susceptibility (χlf), non-hysteresis remanence (χARM) and saturation isothermal remanence (SIRM) have different degrees of correlation with heavy metal elements, and the correlations with Fe, Pb, Cr and Zn are extremely prominent. The magnetic parameters can effectively and quickly reflect the level of particulate matter pollution, making them a useful tool for monitoring urban air quality