Dataset Information

Light Absorption of Secondary Organic Aerosol: Composition and Contribution of Nitroaromatic Compounds.

ABSTRACT: Secondary organic aerosol (SOA) can affect the atmospheric radiation balance through absorbing light at shorter visible and UV wavelengths. However, the composition and optical properties of light-absorbing SOA is poorly understood. In this work, SOA filter samples were collected during individual chamber experiments conducted with three biogenic and eight aromatic volatile organic compound (VOC) precursors in the presence of NOX and H2O2. Compared with the SOA generated using the aromatic precursors, biogenic SOA generally exhibits negligible light absorption above 350 nm; the aromatic SOA generated in the presence of NOX shows stronger light absorption than that generated with H2O2. Fifteen nitroaromatic compound (NAC) chemical formulas were identified and quantified in SOA samples. Their contributions to the light absorption of sample extracts were also estimated. On average, the m-cresol/NOX SOA sample has the highest mass contribution from NACs (10.4 ± 6.74%, w/w), followed by naphthalene/NOX (6.41 ± 2.08%) and benzene/NOX (5.81 ± 3.82%) SOA. The average contributions of NACs to total light absorption were at least two times greater than their average mass contributions at 365 and 400 nm, revealing the potential use of chromophoric NACs as brown carbon (BrC) tracers in source apportionment and air quality modeling studies.

SUBMITTER: Xie M

PROVIDER: S-EPMC7372712 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Light Absorption of Secondary Organic Aerosol: Composition and Contribution of Nitroaromatic Compounds.

Xie Mingjie M Chen Xi X Hays Michael D MD Lewandowski Michael M Offenberg John J Kleindienst Tadeusz E TE Holder Amara L AL

Environmental science & technology 20170929 20

Secondary organic aerosol (SOA) can affect the atmospheric radiation balance through absorbing light at shorter visible and UV wavelengths. However, the composition and optical properties of light-absorbing SOA is poorly understood. In this work, SOA filter samples were collected during individual chamber experiments conducted with three biogenic and eight aromatic volatile organic compound (VOC) precursors in the presence of NOX and H2O2. Compared with the SOA g ...[more]

PMID: 28930472

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Project description:This study seeks to understand the compositional details of N-containing aromatic compounds (NACs) emitted during biomass burning (BB) and their contribution to light-absorbing organic carbon (OC), also termed brown carbon (BrC). Three laboratory BB experiments were conducted with two U.S. pine forest understory fuels typical of those consumed during prescribed fires. During the experiments, submicron aerosol particles were collected on filter media and subsequently extracted with methanol and examined for their optical and chemical properties. Significant correlations (p < 0.05) were observed between BrC absorption and elemental carbon (EC)/OC ratios for individual burns data. However, the pooled experimental data indicated that the BB BrC absorption depends on more than the BB fire conditions as represented by the EC/OC ratio. Fourteen NAC formulas were identified in the BB samples, most of which were also observed in simulated secondary organic aerosol (SOA) from photo-oxidation of aromatic VOCs with NOX. However, the molecular structures associated with the identical NAC formula from BB and SOA are different. In this work, the identified NACs from BB are featured by methoxy and cyanate groups, and are predominately generated during the flaming phase. The mass concentrations of identified NACs were quantified using authentic and surrogate standards, and their contributions to bulk light absorption of solvent extractable OC were also calculated. The contributions of identified NACs to organic matter (OM) and BrC absorption were significantly higher in flaming-phase samples than those in smoldering-phase samples, and correlated with EC/OC ratio (p < 0.05) for both individual burns and pooled experimental data, indicating that the formation of NACs from BB largely depends on burn conditions. The average contributions of identified NACs to overall BrC absorption at 365 nm ranged from 0.087 ± 0.024 to 1.22 ± 0.54%, 3 - 10 times higher than their mass contributions to OM (0.023 ± 0.0089 to 0.18 ± 0.067%), so the NACs with light absorption identified in this work from BB are likely strong BrC chromophores. Further studies are warranted to identify more light-absorbing compounds to explain the unknown fraction (> 98%) of BB BrC absorption.

Project description:The analytical capabilities associated with the use of silylation reactions have been extended to a new class of organic molecules, nitroaromatic compounds (NACs). These compounds are a possible contributor to urban particulate matter of secondary origin which would make them important analytes due to their (1) detrimental health effects, (2) potential to affect aerosol optical properties, and (3) and usefulness for identifying PM2.5 from biomass burning. The technique is based on derivatization of the parent NACs by using N,O-bis-(trimethylsilyl)-trifluoro acetamide, one of the most prevalent derivatization reagent for analyzing hydroxylated molecules, followed by gas chromatography-mass spectrometry using electron ionization (EI) and methane chemical ionization (CI). This method is evaluated for 32 NACs including nitrophenols, methyl-/methoxy-nitrophenols, nitrobenzoic acids, and nitrobenzyl alcohols. Electron ionization spectra were characterized by a high abundance of ions corresponding to [M+ ] or [M+ - 15]. Chemical ionization spectra exhibited high abundance for [M+ + 1], [M+ - 15], and [M+ + 29] ions. Both EI and CI spectra exhibit ions specific to nitro group(s) for [M+ - 31], [M+ - 45], and [M+ - 60]. The strong abundance observed for [M+ ] (EI), [M+ - 15] (EI/CI), or [M+ + 1] (CI) ions is consistent with the high charge stabilizing ability associated with aromatic compounds. The combination of EI and CI ionization offers strong capabilities for detection and identification of NACs. Spectra associated with NACs, containing hydrogen, carbon, oxygen, and nitrogen atoms only, as silylated derivatives show fragment/adduct ions at either (a) odd or (b) even masses that indicate either (a) odd or (b) even number of nitro groups, respectively. Mass spectra associated with silylated NACs exhibited 3 distinct regions where characteristic fragmentation with a specific pattern associated with (1) ─OH and/or ─COOH groups, (2) ─NO2 group(s), and (3) benzene ring(s). These findings were confirmed with applications to chamber aerosol and ambient PM2.5 .

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Dataset Information

Light Absorption of Secondary Organic Aerosol: Composition and Contribution of Nitroaromatic Compounds.

Publications

Light Absorption of Secondary Organic Aerosol: Composition and Contribution of Nitroaromatic Compounds.

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