Health impacts of long-range transported air pollution in South America: compound events, cascading hazards and the Pantanal 2020 fire crisis.

Human-induced climate changes have increased the frequency of simultaneous hot–dry events. In 2020, the occurrence of compound droughts and heat waves (CDHW) conditions in the Pantanal (the largest continuous tropical wetland located in central-western Brazil) exacerbated fire risk, leading to unusual amounts of burned area (BA). Despite the well-documented local impacts on the ecosystem and economy, besides regional effects that included black sky episodes in South and Southeastern Brazil, the number of studies investigating the long-range impacts associated with Pantanal fires is still limited, compared to Amazon and Cerrado biomes. Here, we analyzed the long-range transport of smoke from the Pantanal during the 2020 mega fires to the São Paulo state (SPS) and the cascading impacts on air quality and human health statewide, integrating observational, satellite-based, and reanalysis data and atmospheric dispersion models. Three main episodes of transport of smoke-related to peaks of fire events in the Pantanal were identified through air mass trajectories simulated with HYSPLIT, leading to a substantial enhancement in PM2.5 levels over SPS, surpassing World Health Organization guidelines by over 70%-600% in different regions of the state. The EURAD-modeled PM2.5 concentrations during the fire episode aligned with those observed from air quality monitoring stations. Model results highlighted the key role of the South American Low-Level Jet (SALLJ) in the redistribution of smoke plumes in South America, as previously observed in central Brazil and the Amazon basin. Two smoke-induced air pollution episodes coincided with heat waves observed in the SPS, contributing to worsening air quality and amplifying health risks. Thus, the period between October 1st and October 14th was marked by excess mortality of 2,150 (2,095 - 2,206) over 14 days, representing a 21% (17-24%) mortality increase. The impact on mortality was higher in the northwestern SPS, regions more affected by the transported smoke. Our findings reinforce the need to implement public policies associated with fire control and management in the Pantanal, considering the country's large-scale interactions among different regions and biomes, besides adaptation strategies to concurrent and cascading extreme events expected to increase under any future global warming scenarios.