Enhanced aerosols over the southeastern Tibetan Plateau induced by open biomass burning in spring 2020

The Tibetan Plateau is the third pole of the world, with an essential role in regulating Northern Hemisphere climate. Previous studies showed that atmospheric aerosols over the Tibetan Plateau are influenced by biomass burning (BB) products from South and Southeast Asia. In fact, open biomass burning (OBB) is also an important form of BB in Southeast Asian countries, causing serious springtime air pollution yearly. However, there are still scientific gaps in the contribution of OBB to surrounding regional aerosols, especially on the Tibetan Plateau. In order to quantify this contribution, we collected samples of fine particulate matter and derived the concentrations of major water soluble ion, water soluble organic carbon (WSOC), and total carbon (TC) and total nitrogen (TN) as well as the dual isotopic compositions of carbon and nitrogen (δ¹³C and δ¹⁵N) during March-June on the southeastern Tibetan Plateau. δ¹³C and δ¹⁵N showed no significant difference (p > 0.05) between the OBB and non-OBB periods. Furthermore, both δ¹³C and δ¹⁵N (-25.7 ± 0.7 ‰ and 8.0 ± 3.6 ‰) values calculated during the whole sampling period were similar to the BB value, indicating that the primary source of TC and TN in aerosols was BB, whether OBB or non-OBB burning periods. TC and TN concentrations during the OBB period (6.5 ± 2.9 μg m^-3 and 1.2 ± 0.4 μg m^-3, respectively) were significantly higher than during the non-OBB period (4.1 ± 1.7 μg m^-3, with p = 0.014, and 0.7 ± 0.3 μg m^-3, with p = 0.013, respectively). Active fire data and surface smoke concentrations further indicated that BB emissions from Southeast Asia were higher during the OBB period. This suggests that OBB-related high BB emissions significantly enhanced atmospheric aerosols concentrations on the southeastern Tibetan Plateau.