Brown carbon (BrC) is an aerosol carbonaceous matter that absorbs light at the near-ultraviolet and visible (UV-vis) wavelengths (Andreae & Gelencser, 2006;Kirchstetter et al., 2004). BrC has an important impact on atmospheric radiation and global climate (Feng et al., 2013;Zhang et al., 2017). BrC is also actively involved in atmospheric chemistry (Jacobson, 1999). For example, some BrC chromophores, such as imidazole-2-carboxaldehyde, can trigger photosensitized reactions (Kampf et al., 2012;Lee et al., 2013;Powelson et al., 2014). Triplet excited BrC participated in aerosol aging by generating singlet molecular oxygen (Kaur et al., 2019). BrC in cloud/fog water can accelerate water evaporation and cloud dissipation by absorbing light and thus affect the indirect effect of aerosols (Hansen et al., 1997).

Abstract. Iodine-initiated new particle formation (I-NPF) has long been recognized in coastal hotspot regions. However, no prior work has studied the exact chemical composition of organic compounds and their role in coastal I-NPF. Here we present an important complementary study to the ongoing laboratory and field research on iodine nucleation in the coastal atmosphere. Oxidation and NPF experiments with vapor emissions from real-world coastal macroalgae were simulated in a bag reactor. On the basis of comprehensive mass spectrometry measurements, we reported for the first time a variety of volatile precursors and their oxidation products in gas and particle phases in such a highly complex system. Organic compounds overwhelmingly dominated over iodine in the new particle growth initiated by iodine species. The identity and transformation mechanisms of organic compounds were proposed in this study to provide a more complete story of coastal NPF from low-tide macroalgal emission.

We present a data analysis workflow for nontarget tandem high-resolution mass spectrometry (MS), with the aim being full speciation of functionalized organic compounds in complex atmospheric samples without unambiguous molecular structure assignment. The workflow was demonstrated for four types of samples, including primary-emission aerosols, secondary organic aerosols, ambient aerosols, and rainwater, but could be applicable to other environmental samples. With a single mass spectrometry run, the combined MS1 and MS2 analysis provided molecular formula, functional group, and aromaticity information for 68.1–88.8% of deprotonated molecules and 58.6–84.7% of protonated molecules. We determined relative abundances of 22 and 21 compound categories for deprotonated and protonated molecules, respectively, on the basis of the assignment of a variety of oxygen-, nitrogen-, and sulfur-containing functional groups. Molar concentrations of compound categories were further semiquantified with surrogate standards in electrospray ionization negative mode, ranging from 10–4 to 1 nmol (μg of source aerosol mass)−1, from 3 × 10–3 to 2 nmol m–3 in the atmosphere, and from 2 × 10–3 to 1 nmol (mL of rainwater)−1. The assignment and quantification of functional groups provided new chemical fingerprints of organic compounds to trace their sources, formation, and aging in the atmosphere and also allowed the use of group contribution methods to study the physicochemical properties of organic aerosols.

This a preprint and has not been peer reviewed. Data may be preliminary.

Abstract. Iodine-initiated new particle formation (I-NPF) has long been recognized in coastal hotspot regions. However, no prior work has studied the exact chemical composition of organic compounds and their role in the coastal I-NPF. Here we present an important complementary study to the ongoing laboratory and field researches of iodine nucleation in coastal atmosphere. Oxidation and NPF experiments with vapor emissions from real-world coastal macroalgae were simulated in a bag reactor. On the basis of comprehensive mass spectrometry measurements, we reported for the first time a variety of volatile precursors and their oxidation products in gas and particle phases in such a highly complex system. Organic compounds overwhelmingly dominated over iodine in the new particle growth initiated by iodine species. The identity and transformation mechanisms of organic compounds were proposed in this study to provide a more complete story of coastal NPF from low-tide macroalgal emission.