Impacts of land use change and interannual climate variability on biomass burning emissions, air quality and public health in Amazon

Biomass burning in Amazon Basin has a significant impact on regional climate and deteriorates regional air quality, which poses a threat to human and ecosystem health. The fire-induced pollution worsens during dry season (Jul to Nov) and shows a strong seasonal variation. Past research has demonstrated that the occurrence of wildfires in Amazon is not only influenced by deforestation, but also interannual climate variability, particularly droughts. Here we estimate the impacts of deforestation and droughts on fire emissions and regional air quality between 2010 to 2015 by using Global Fire Emission Database Version 4 (GFED v4) to drive a global 3-D atmospheric chemical transport model GEOS-Chem High Performance (GCHP) and further examine the effect of PM_2.5 and O₃ on premature mortality across the region. By comparing the “fire-on” and “fire-off” scenarios, we find that biomass burning alone in normal years (2011 and 2013) contributes 5.7 μg m^-3 (47.6% of the total concentration) PM_2.5, 0.08 ppm (46.3%) CO, 0.03 ppb (85.0%) NO_x, and 9.5 ppb (41.2%) O₃; and these numbers during drought years (2010, 2012, 2014 and 2015) increase to 19.6 μg m^-3 (74.7%) for PM_2.5, 0.20 ppm (67.0%) for CO, 0.19 ppb (97.4%) for NO_x, and 15.6 ppb (52.0%) for O₃. We find that these pollutants from wildfires mainly concentrate in the south-eastern Amazon and then transport southward, thus strongly impacting public health in the downwind regions. We estimate that premature mortality due to long-term exposure to particulate matter and ozone by applying the simulated concentration to the concentration-response functions from the European Environment Agency. We find that ~8,500 and ~10,400 deaths per year are attributable to PM_2.5 and O₃ exposure for 2010-2015 respectively. During drought years, we discover there are 2.8% and 3.4% more deaths than normal years for PM_2.5 and O₃ exposure. Our study shows the significance of biomass burning emissions in shaping the air quality in the Amazon region, and highlights the impact of drought events on enhancing biomass emissions, worsening regional air quality and causing public health issues. Therefore, it is important to address the underlying causes of biomass burning in the Amazon, such as deforestation and land use change, and droughts, to protect the region's ecosystems and mitigate the impacts of climate change.