Characterization of carbonaceous aerosols in Singapore: insight from black carbon fragments and trace metal ions detected by a soot particle aerosol mass spectrometer

Abstract

Abstract. Understanding sources and atmospheric processes that can influence the physiochemical properties of carbonaceous aerosols is essential to evaluate their impacts on air quality and climate. However, resolving the sources, emission characteristics, and aging processes of carbonaceous aerosols in complex urban environments remains challenging. In this work, a soot particle aerosol mass spectrometer (SP-AMS) was deployed to characterize organic aerosols (OAs), refractory black carbon (rBC), and trace metals in Singapore, a highly urbanized city with multiple local and regional air pollution sources in the tropical region. rBC (C1+–C9+) fragments and trace metal ions (K+, Na+, Ni+, V+, and Rb+) were integrated into our positive matrix factorization of OA. Two types of fossil fuel combustion-related OAs with different degrees of oxygenation were identified. This work provides evidence that over 90 % of rBC originated from local combustion sources with a major part related to traffic and ∼30 % associated with fresh secondary organic aerosol (SOA) produced under the influence of shipping and industrial emission activities (e.g., refineries and petrochemical plants) during daytime. The results also show that ∼43 % of the total rBC was emitted from local traffic, while the rest of the rBC fraction stemmed from multiple sources including vehicular sources, shipping, and industrial emissions, but was not fully resolved. There was only a weak association of the cooking-related OA component with rBC. Although there was no observable biomass burning episode during the sampling period, K+ and Rb+ were mainly associated with the more oxidized oxygenated OA component, indicating the potential contribution of regional biomass burning and/or coal combustion emissions to this aged OA component. Furthermore, the aerosol pollutants transported from the industrial area and shipping ports presented higher C1+/C3+ and V+/Ni+ ratios than those associated with traffic. The observed association between Na+ and rBC suggests that the contribution of anthropogenic emissions to total particulate sodium should not be ignored in coastal urban environments. Overall, this work demonstrates that rBC fragments and trace metal ions can improve our understanding of the sources, emission characteristics, and aging history of carbonaceous aerosol (OA and rBC) in this type of complex urban environment.

Technical note: A new approach to discriminate different black carbon sources by utilising fullerene and metals in positive matrix factorisation analysis of high-resolution soot particle aerosol mass spectrometer data

“…In the previous research, PMF has been used extensively to apportion organics with the standard AMS data but not so often to apportion BC from SP-AMS data Saarikoski et al, 2014). In this research study positive matrix factorisation (PMF) was applied to HR-SP-AMS data to apportion BC in to more than two sources.…”

Elemental analysis of oxygenated organic coating on black carbon particles using a soot-particle aerosol mass spectrometer

“…The average enhancement factor of f C 2 H 4 O + 2 for alcohol, dicarboxylic acids, and multifunctional groups are 2.62 ± 0.92, 2.90 + 0.78, and 2.69 ± 1.11, respectively. Levoglucosan, a known cellulose-derived compound produced during biomass burning (Simoneit et al, 1999), gives an enhancement of f C 2 H 4 O + 2 by a factor of 2.33. Different to f C 2 H 3 O + /f CO + 2 ratios that show scattered data between vaporization schemes, a strong linear correlation was obtained for all the tested species (R = 0.95) with the slope equal to 2.45.…”

Sources of black carbon at residential and traffic environments

“…In terms of the PMF analysis for the refractory material, rBC and metal fragments are typically included in the mass spectra matrix of organics. For example, Rivellini et al (2020) found five sources for rBC, trace metals and organics in the ambient air of Singapore by applying PMF to the SP-AMS data while Bibi et al (2020) utilized PMF to separate rBC originated from bonfires and domestic wood burning in UK. On the other 60 hand, have investigated the sources of rBC in an underground mine with PMF and Carbone et al (2019) have distinguished fuel and lubricating oil related rBC in the diesel engine exhaust particles in the laboratory by using PMF for the mass spectra of rBC, organics and metals.…”

“…One disadvantage of using PMF for the SP-AMS data is that the mass spectra of rBC contains relatively few fragments (typically largest signal observed for C1 + -C5 + fragments), and therefore, the identification of the sources is typically based on organic 65 fragments. However, the rBC mass spectra has been noticed to be somewhat source specific differing for example for laboratory generated rBC particles and particles from aircraft turbine (Corbin et al, 2012), diesel truck and biomass burning particles (Onasch et al, 2015), and ambient hydrocarbon like organic aerosol (HOA) and oxygenated organic aerosol (OOA) factors (Rivellini et al, 2020). One option to improve the separation of BC sources is to include larger Cx fragments in the PMF matrix, as was done in the study of Bibi et al (2020), where 70 the addition of fullerenes signals (for example C60 + ) increased the number of meaningful sources.…”