Naphthalene‐Derived Secondary Organic Aerosols Interfacial Photosensitizing Properties

Abstract

We investigated the photosensitizing properties of secondary organic aerosol (SOA) formed during the hydroxyl radical (OH) initiated oxidation of naphthalene. This SOA was injected into an aerosol flow tube and exposed to UV radiation and gaseous volatile organic compounds or sulfur dioxide (SO2). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO2, a photosensitized production (0.2–0.3 µg m−3 h−1) of sulfate was observed at all relative humidity (RH) levels. Some sulfate also formed on particles in the dark, probably due to the presence of organic peroxides. The dark and photochemical pathways exhibited different trends with RH, unraveling different contributions from bulk and surface chemistry. As naphthalene and other polycyclic aromatics are important SOA precursors in the urban and suburban areas, these dark and photosensitized reactions are likely to play an important role in sulfate and SOA formation.

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

“…Photosensitization processes have been reported to contribute to photoenhanced sulfate formation. 29,30,70 In brief, photosensitizers absorb light and transfer from their ground state to a singlet excited state. Some singlet excited state molecules are further converted to their triplet excited state and then oxidize SO 2 .…”

“…Some singlet excited state molecules are further converted to their triplet excited state and then oxidize SO 2 . 29,30 Incense burning emits photosensitizers such as vanillin (VL) (Figure S2). 19,71−74 We aged the atomized KCl+VL mixed particles (mass ratio = 1:1) by SO 2 .…”

“…Photosensitization processes have been reported to contribute to photoenhanced sulfate formation. ,, In brief, photosensitizers absorb light and transfer from their ground state to a singlet excited state. Some singlet excited state molecules are further converted to their triplet excited state and then oxidize SO 2 . , Incense burning emits photosensitizers such as vanillin (VL) (Figure S2). ,− We aged the atomized KCl+VL mixed particles (mass ratio = 1:1) by SO 2 .…”

“…17,28 Recent studies have shown that photosensitization in single model compounds (e.g., naphthalene) and PM 2.5 extracts (as an ensemble of different types of particles or model chemicals) can oxidize SO 2 to sulfate. 29,30 However, there are very limited studies of sulfate formation in incense/biomass burning particles.…”

“…Numerous investigations on incense burning particles have been conducted but mainly focus on the chemical composition and potential health impact of the fresh particles, particularly in the indoor environment. − , However, many incense-burning activities are in outdoor or semi-outdoor environments. After emission, the fresh particles are exposed to other atmospheric pollutants and light, which can result in changes in their physicochemical properties and secondary pollutant (e.g., sulfate) formation. − In particular, NO 2 and peroxides can oxidize SO 2 to sulfate, and soot and transition metals can promote catalytic oxidation of SO 2 by O 2 . − Biomass burning particles have been found to exhibit photosensitization in oxidizing organic precursors to form secondary organic aerosols (SOAs). , Recent studies have shown that photosensitization in single model compounds (e.g., naphthalene) and PM 2.5 extracts (as an ensemble of different types of particles or model chemicals) can oxidize SO 2 to sulfate. , However, there are very limited studies of sulfate formation in incense/biomass burning particles.…”