Abstract

Abstract. Recurring transboundary haze from Indonesian wildfires in previous decades significantly elevated particulate matter (PM) concentrations in Southeast Asia. During that event on 10 to 31 October 2015, we conducted a real-time observation of non-refractory submicron PM (NR-PM1) in Singapore using an Aerodyne aerosol mass spectrometer. Simultaneously, we characterized carbonaceous components and organic aerosol (OA) tracers from fine PM (PM2.5) samples to support source apportionment of the online measurements. The real-time analysis demonstrated that OA accounted for approximately 80 % of NR-PM1 mass during the wildfire haze period. Source apportionment analysis applied to the OA mass spectra using the multilinear-engine (ME-2) approach resulted in four factors: hydrocarbon-like OA (HOA), biomass burning OA (BBOA), peat burning OA (PBOA), and oxygenated OA (OOA). The OOA can be considered as a surrogate of both secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA), while the other factors are considered as surrogates of primary organic aerosol (POA). The OOA accounted for approximately 50 % of the total OA mass in NR-PM1, while POA subtypes from wildfires (BBOA and PBOA) contributed to approximately 30 % of the total OA mass. Our findings highlight the importance of atmospheric chemical processes, which likely include POA oxidation and SOA formation from oxidation of gaseous precursors, to the OOA concentration. As this research could not separately quantify the POA oxidation and SOA formation processes, further studies should attempt to investigate the contribution of gaseous precursor oxidation and POA aging to the OOA formation in wildfire plumes.

Highlights

  • Transboundary haze caused by wildfires has been a recurring issue in Southeast Asia for the past few decades, causing economic and health problems (Atwood et al, 2013; Engling et al, 2014; Heil and Goldammer, 2001; Nichol, 1997, 1998; Pavagadhi et al, 2013)

  • Back-trajectories of air masses arriving at Singapore during this period show that the air mass was influenced by wildfires in Kalimantan and Sumatra, Indonesia (Fig. S6)

  • We found a good correlation (R2 = 0.6–0.7, Table S4 and Fig. 4b) between peat burning OA (PBOA) and levoglucosan as well as the sum of Brown carbon (BrC) constituents characterized from laboratory peat burning aerosol and the ambient samples of the 2015 haze event (Budisulistiorini et al, 2017a)

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Summary

Introduction

Transboundary haze caused by wildfires has been a recurring issue in Southeast Asia for the past few decades, causing economic and health problems (Atwood et al, 2013; Engling et al, 2014; Heil and Goldammer, 2001; Nichol, 1997, 1998; Pavagadhi et al, 2013). Haze occurrence has been associated with anomalously low precipitation induced by the El Niño Southern Oscillation and the Indian Ocean Dipole (Field et al, 2009, 2016; Gaveau et al, 2015). During the 1997 El Niño period, the wildfires in Indonesia consumed both peat and surface vegetation and caused a severe transboundary haze (Heil and Goldammer, 2001)

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