Sulfate Formation in Incense Burning Particles: A Single-Particle Mass Spectrometric Study

Abstract

Incense burning is a common ritual in Asian communities, and it emits massive amounts of particles. These particles can undergo atmospheric aging upon exposure to sunlight and other pollutants. In this work, we observed sulfate formation in fresh incense particles upon exposure to SO 2 , using a single-particle aerosol mass spectrometer (SPAMS). Analysis of the positive mass spectra classified the particles as K-type and OC-type. In both dark and light experiments, SO 2 uptake and oxidation were found preferentially in OC-type particles over K-type particles. Sulfate formation, as represented by the number fraction of sulfate-containing particles (FS), under dark was likely due to gaseous oxidants. FS increased with UV, mainly attributable to photosensitization reactions. While more sulfate formed at higher relative humidity (RH) under dark, sulfate formation under light was independent of RH. The increase in FS due to photochemistry was more effective under lower RH, where the photoactive compounds were more concentrated and likely generated more photo-oxidants. This effect outweighed that due to reduced SO 2 dissolution. Since incense burning particles contain organic photosensitizers that have also been found in biomass burning particles, our findings could shed light on the potential of biomass burning particles to trigger sulfate formation.

Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation

“…The relative peak area (RPA), defined as the peak area of a specific peak divided by the total positive or negative mass spectral peak area, can reflect the relative abundance of particulate components (Liang et al, 2022a). The average spectra of the incense burning particles (Figure 1a) are similar to our previous work on incense burning at 50% RH (Liang et al, 2022b). +39 [K] dominates the positive spectra, and organic nitrogen (ON) peaks (i.e., -26 [CN] and -42 [CNO]) from nitrogen-containing organics (NOC) dominate the negative spectra Zhai et al, 2015;.…”

“…The average spectra of each category can be found in Figure S2. There are slightly fewer K-ON particles and more K-ONEC particles observed at 80% RH (this work) than at 50% RH in Liang et al (Liang et al, 2022b), probably due to the lower organic concentrations at higher RH to limit particle-phase partitioning of volatile organic compounds (Donaldson and Vaida, 2006;Mcfall et al, 2020;Chan and Chan, 2011;Chan et al, 2010). Overall, the number fraction (NF) of each category is similar to our previous work, with a descending order of K-ON (47.3±5.2%) >> OC-ON (25.7±4.7%) ≈ K-ONEC (20.2±2.8%) > K-Cl (5.1±1.1%) (Figure 1c), reflecting the fresh incense burning particles are organic-rich (Li et al, 2012;.…”

“…In descending order, the NF of oxalate and malonate was K-N > K-ONN > OC-N. The mass hygroscopic grow factor (i.e., the mass ratio of wet particles to dry particles) of inorganic potassium salts KNO3 and KCl at 80% RH are around 1.6 and 2.2 based on AIOMFAC model predictions (Text S1, https://aiomfac.lab.mcgill.ca/about.html (Zuend et al, 2008)), much higher than that in the water extract of biomass burning particles (1.1-1.4, including both lab-generated and ambient collected) (Rissler et al, 2006;Carrico et al, 2008;Chan et al, 2005), as well as fresh incense burning particles (around 1) (Liang et al, 2022b), which are organic-rich. The likely higher fraction of hygroscopic inorganic of inorganic fraction allows K-N and K-ONN to retain more liquid water to dissolve gaseous SOA precursors for oxalate and malonate formation.…”

Sulfate formation via aerosol phase SO2 oxidation by model biomass burning photosensitizers: 3,4-dimethoxybenzaldehyde, vanillin and syringaldehyde using single particle characterization

“…area (RPA, defined as the fractional contribution of the targeted ion peak area to the sum of all ion peak areas) were applied to indicate the variations of different species (e.g., sulfate) in individual particles (Hu et al, 2022). Sulfate-containing particles were distinguished by m/z -97 [HSO4 -] or m/z-96 [SO4 -] ( Guazzotti et al, 2001;Liang et al, 2022). In addition, an adaptive resonance theory based neural network algorithm (ART-2a) (Li et al, 2011) was used to separate and cluster particles in external and internal mixtures according to the similarities in individual mass spectra of single particles.…”

In-depth study of the formation processes of single atmospheric particles in the southeastern margin of Tibetan Plateau

“…In this study, we chose the relative number fractions of 43 C2H3O + , 89 HC2O4 − , 62 NO3 − , 97 HSO4 − , and 18 NH4 + -containing particles to the total detected particles to indicate the secondary formation (Liang et al, 2022), respectively. The correlations between the number fraction of each secondary species with the oxidant concentrations (Ox = O3 + NO2) and RH are used to reflect the formation pathways during the two events (Chen et al, 2016).…”