Dominant contribution of oxygenated organic aerosol to haze particles from real-time observation in Singapore during an Indonesian wildfire event in 2015

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.

Changes in PM<sub>2.5</sub> peat combustion source profiles with atmospheric aging in an oxidation flow reactor

“…These patterns, termed "source profiles," have been measured in diluted exhaust emissions and resuspended mineral dusts for a variety of representative emitters. Many of these source profiles are compiled in country-specific source profile data bases (Cao, 2018;CARB, 2019;Liu et al, 2017;Mo et al, 2016;Pernigotti et al, 2016; and have been widely used for source apportionment and speciated emission inventories.…”

“…Despite this lack of peat-specific fresh and aged source profiles, results have been published for source apportionment in Indonesia (See et al, 2007), Malaysia (Fujii et al, 2017), Singapore (Budisulistiorini et al, 2018), and Ireland (Dall'Osto et al, 2013;Kourtchev et al, 2011;Lin et al, 2019). These have involved sampling under environments dominated by near-source and far-from-source emissions, such as the 2015 Indonesia burning episode, to determine changes in thermally derived carbon fractions with aging (Tham et al, 2019) and inference of aged peat burning profiles from positive matrix factorization (PMF) application to chemically speciated ambient PM samples (Fujii et al, 2017).…”

Constraining the Emission of Particulate Matter From Indonesian Peatland Burning Using Continuous Observation Data

“…Peat sampled in Riau province contains small (~0.1%) fraction of sulfur (Budisulistiorini et al, ; Neuzil et al, ). In addition, aerosol particles emitted from Indonesian peat combustion also include sulfur containing species (Budisulistiorini et al, ; Ikegami et al, ).…”

“…In addition, aerosol particles emitted from Indonesian peat combustion also include sulfur containing species (Budisulistiorini et al, ; Ikegami et al, ). Sulfate concentration in Singapore increased when the country was covered by wildfire haze transported from Indonesia (Budisulistiorini et al, ). These results could be considered as supporting evidence that combustion of Indonesian peat emit SO 2 to the atmosphere.…”

“…Emission of sulfur dioxide (SO 2 ), which is an important precursor of aerosol particles, from peatland burning is also uncertain, even though tropical peatland contains sulfur (Budisulistiorini et al, ; Langmann & Graf, ; Neuzil et al, ). An experimental combustion of tropical peat indicated that the combustion of tropical peat emitted SO 2 (SO 2 /CO = 0.011 ± 0.004 g g −1 ; Othman & Latif, ).…”