The hidden risk in high-temperature urban environments: assessment of metal elements and human health risks of particulate matter at street.

With the exacerbated urban heat island effect, urban populations are exposing to high temperatures and increased exposure to particulate matter (PM) during daily commutes (especially vulnerable groups). Under high-temperature urban environments, the traffic emissions and the individual respiratory rate would rise simultaneously, causing an elevated risk of air particulate exposure. Most previous studies on PM at bus stations have focused on concentration levels, while neglecting chemical analyses of metal elements or increased human respiratory intake in high-temperature environments. This study conducted PM sampling and physiological parameter measurements of waiting passengers under high temperature conditions at six distinct bus stations in Nanjing. The health risks associated with exposure to metallic elements were evaluated alongside the impact of elevated temperatures on human health, employing chemical analyses to substantiate these assessments. The results indicated that the average PM concentration at bus stations exceeded the urban background by approximately 15 μg/m³, while As, Cd, and Cr were identified as hazards posing significant health risks. Notably, under high-temperature conditions, the core body temperature of individuals reached 37.91 °C, with the health risk increasing by around 20-30 %. In view of the risk of human being exposed to high temperature environment, active and passive mitigation measures are proposed.