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Characterization of the Complex Mixture of Urban and Biomass Burning Aerosols Under the Influence of Transboundary Smoke Haze in Southeast Asia
LAURA-HELENA RIVELLINI, Nethmi Kasthuriarachchi, Mutian Ma, Alex Lee, National University of Singapore
Abstract Number: 283
Working Group: Urban Aerosols
Abstract
Biomass burning (BB) emissions, including agricultural burning, peat fires and tropical forest wildfires, in Southeast Asia (SEA) can impact air quality and climate at local and regional scales. The mixture of BB and urban emissions together with active photochemistry encountered in SEA outflow lead to complex transboundary haze. In this study, a soot-particle aerosol mass spectrometer (SP-AMS) was deployed in Singapore, a highly urbanised city in SEA, to investigate BB and typical urban emissions over the northeast and southwest monsoons in 2019. The SP-AMS was operated with the dual vaporization scheme so that non-refractory particulate matter, refractory black carbon (rBC), and trace metals could be characterized simultaneously with a single instrument.
The inclusion of rBC and trace metal in positive matrix factorization (PMF) allows better identification of distinctive types of BB organic aerosol (BBOA) for each monsoon period compared to conventional PMF approach. BBOA components were clearly identified during both periods but they exhibited different chemical characteristics. In particular, the southwest monsoon was strongly impacted by transboundary smoke haze caused by Indonesian wildfires. Our results show that BBOA from transboundary smoke was highly oxygenated and associated different trace metals (e.g., K+, Rb+, Tl+ and Mn+). In contrast, the BBOA component identified during the northeast monsoon gave intense signals at C2H4O2+ (i.e., BBOA tracer), suggesting relatively fresh emissions, and higher N:C ratio. Although its associations with refractory materials were weak, it was correlated with a hydrocarbon-like OA with low refractory carbon association. Concurrent optical measurements further indicate that the transboundary smoke haze was less light absorptive compared to the one identified during northeast monsoon. This provides first field evidence that the types of BB and/or atmospheric processing can have substantial impacts on the chemical characteristics and light absorption properties of BBOA in Southeast Asia.