Using a Pollution-to-Risk Method to Evaluate the Impact of a Cold Front: A Case Study in a Downstream Region in Southeastern China

Cold fronts frequently intrude China in winter, causing air pollution episodes in downwind regions. Fine particulate matter (PM_2.5) has been used as a major proxy of air pollution to examine the impacts of cold fronts. Compared to particles, gaseous pollutants can cause comparable or even higher levels of short-term health risks. In this study, a pollution-to-risk model was used to systematically evaluate the impacts of cold fronts on the combined health risks of air pollution mixtures, including PM_2.5, nitrogen dioxide (NO₂), ozone (O₃), and sulfur dioxide (SO₂). Dominant pollutants that caused significant mortality risks during a cold frontal passage in December 2019 over Fuzhou, a downwind city in southeastern China, were then examined. Under northerly frontal airflows, a pollution belt propagated southwards. In Fuzhou, two pollution peaks existed during the cold frontal passage. At the first peak, convergence and stagnant air in the frontal zone rapidly accumulated local air pollutants. The dominant pollutants that caused the mortality risk were identified as NO₂ and PM_2.5, both of which contributed 45% to the total risk. At the second peak, advection transported a significant amount of secondary pollutants from the upwind regions. Although PM_2.5 was the dominant pollutant at this peak, gaseous pollutants still accounted for 34% of the total risk. Our risk analyses underscore the significant health impacts of gaseous pollutants during cold frontal passages in winter. The results generated from this study will help guide environmental policy makers in forming and improving air pollution control strategies during pollution episodes.