Large presence of bromine and toxic metals in ambient fine particles from urban fires

Urban fires in densely populated areas can burn large amounts of manmade structures and synthetic materials. Realworld chemical composition data of urban fire plumes are vital for evaluating health impacts; however, they are rarely available. Online monitoring of trace elements in ambient PM2.5 at five sites throughout Hong Kong in 2021 provided unprecedented opportunities to observe the highly transient fire plumes. Sharp spikes were captured for bromine (up to 0.65 μg m−3), chlorine (7.0 μg m−3), and certain metals such as lead (0.97 μg m−3), zinc (8.3 μg m−3), and copper (0.32 μg m−3) during four urban fires, showing ∼10–6000 times higher concentrations than pre-fire periods. These elements showed decreased concentrations with increased distance from the fire location, but their concentration ratios remained relatively constant. During fire-influenced hours, these elements exhibited 3–101 times enrichment relative to iron, an element that had no discernible increase in concentration. Our results represent the first observation of the co-emissions of Br and certain metals from urban fires. Reactive bromine released from burning of the wide-spread brominated synthetic chemicals was suggested to facilitate the mobilization of toxic metals into the atmosphere. This mechanistic knowledge will help us understand the emissions and impacts of fires occurring in wildland urban interface zones. The work also calls attention to previously overlooked influence of urban fires-mobilized metals on human health and of bromine on atmospheric oxidizing capacity in megacities.