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Optical Properties of Secondary Organic Aerosol Produced by Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds.

ABSTRACT: Nighttime oxidation of biogenic volatile organic compounds (BVOCs) by nitrate radicals (NO₃·) represents one of the most important interactions between anthropogenic and natural emissions, leading to substantial secondary organic aerosol (SOA) formation. The direct climatic effect of such SOA cannot be quantified because its optical properties and atmospheric fate are poorly understood. In this study, we generated SOA from the NO₃· oxidation of a series BVOCs including isoprene, monoterpenes, and sesquiterpenes. The SOA were subjected to comprehensive online and offline chemical composition analysis using high-resolution mass spectrometry and optical properties measurements using a novel broadband (315-650 nm) cavity-enhanced spectrometer, which covers the wavelength range needed to understand the potential contribution of the SOA to direct radiative forcing. The SOA contained a significant fraction of oxygenated organic nitrates (ONs), consisting of monomers and oligomers that are responsible for the detected light absorption in the 315-400 nm range. The SOA created from β-pinene and α-humulene was further photochemically aged in an oxidation flow reactor. The SOA has an atmospheric photochemical bleaching lifetime of >6.2 h, indicating that some of the ONs in the SOA may serve as atmosphere-stable nitrogen oxide sinks or reservoirs and will absorb and scatter incoming solar radiation during the daytime.

SUBMITTER: He Q

PROVIDER: S-EPMC8023652 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature

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Optical Properties of Secondary Organic Aerosol Produced by Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds.

He Quanfu Q Tomaz Sophie S Li Chunlin C Zhu Ming M Meidan Daphne D Riva Matthieu M Laskin Alexander A Brown Steven S SS George Christian C Wang Xinming X Rudich Yinon Y

Environmental science & technology 20210217 5

Nighttime oxidation of biogenic volatile organic compounds (BVOCs) by nitrate radicals (NO<sub>3</sub>·) represents one of the most important interactions between anthropogenic and natural emissions, leading to substantial secondary organic aerosol (SOA) formation. The direct climatic effect of such SOA cannot be quantified because its optical properties and atmospheric fate are poorly understood. In this study, we generated SOA from the NO<sub>3</sub>· oxidation of a series BVOCs including isop ...[more]

PMID: 33596062

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Project description:The nitrate radical (NO3) oxidation of isoprene is an important contributor to secondary organic aerosol (SOA). Isoprene has two double bonds which allow for multigeneration oxidation to occur. The effects of multigeneration chemistry on the gas- and particle-phase product distributions of the isoprene + NO3 system are not fully understood. In this study, we conduct chamber experiments by varying the ratio of N2O5 (precursor of NO3) to isoprene concentration from 1:1 to 14:1 to investigate the formation of products in both phases under different oxidation levels. Multigeneration chemistry leads to the formation of gas-phase products which then partition into particle phase depending on the product volatility; first-generation products (15-36% of total SOA) such as C5H9NO5 and C10H16N2O9 have volatility (log10C* = 1.0-3.0 using the partitioning method and log10C* = 2.6-4.5 using the formula method) 1-5 orders of magnitude higher than second-generation products (37-57% of total SOA, log10C* = -0.8-2.1 using the partitioning method and log10C* = -3.7-1.8 using the formula method) such as C5H8,10N2O8, C5H9N3O10, and C10H17N3O13. The fast reaction rate constants of first-generation products (estimated to be on the order of 10-13 cm3 molecules-1 s-1 at 295 K) and the lower volatility of second-generation products result in increased SOA yields when NO3 availability increases and multigeneration chemistry is enhanced. Specifically, an increase of up to 300% in SOA yield is observed when the N2O5/isoprene ratio increases from 1:1 to 3:1; from 5.7% (organic aerosol mass concentration, ΔM o = 4.2 μg/m3) to 16.3% (ΔM o = 11.9 μg/m3) when the reacted isoprene concentration is 25 ppb and from 3.1% (ΔM o = 1.2 μg/m3) to 12.4% (ΔM o = 5.4 μg/m3) when the reacted isoprene concentration is 15 ppb. The maximum SOA yield occurs when the N2O5/isoprene ratio is greater than or equal to 3:1 as a combined result of multigeneration chemistry and peroxy radicals (RO2) fate. We encourage future studies to consider both factors, which can vary under different laboratory and ambient conditions, when comparing SOA yields to better understand any differences observed. Our results highlight that multigeneration chemistry and the updated parameters including reaction rate constants and volatility distribution of products should be considered to enable a more comprehensive representation and prediction of SOA formation from NO3 oxidation of isoprene in atmospheric models.

Dataset Information

Optical Properties of Secondary Organic Aerosol Produced by Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds.

Publications

Optical Properties of Secondary Organic Aerosol Produced by Nitrate Radical Oxidation of Biogenic Volatile Organic Compounds.

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