Impacts of the 2019 extreme Indonesian wildfires on black carbon across Southeast Asia

The late dry season of 2019 featured one of the most severe Indonesian wildfire events of the past decade, driven by persistent drought and extensive peatland burning. These extreme wildfires emitted large amounts of carbonaceous aerosols, substantially degrading air quality and posing risks to human health. However, the impacts of extreme wildfire events on black carbon (BC) across Southeast Asia remain poorly quantified. Here, we evaluate the influence of Indonesian wildfires during August–October 2019 using the GEOS-Chem chemical transport model at 0.25° × 0.3125° resolution. Sensitivity simulations with and without Indonesian fire emissions are conducted to isolate fire-driven contributions to BC. Results indicate dominant wildfire control over BC across Southeast Asia. Fire contributions reach about 91% over both Borneo and Sumatra during peak burning. Comparable fire influence extends to nearby seas, particularly the South China Sea, with contributions exceeding 90% over the southern South China Sea. Contributions remain near 70% over the Sulu and Celebes Seas and still reach about 50% over the Philippine Sea. In contrast, impacts over the East China Sea are episodic, occurring only during short-lived northeastward outflow events. These findings demonstrate the strong and spatially heterogeneous influence of Indonesian wildfires on regional BC across Southeast Asia, highlighting the role of extreme wildfire events in shaping air quality through fire-driven transboundary transport.