ORCID Profile
0000-0003-0891-0052
Current Organisation
University of California, Irvine
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Publisher: Copernicus GmbH
Date: 02-01-2019
Publisher: Copernicus GmbH
Date: 13-05-2020
Abstract: Abstract. Secondary organic aerosol (SOA) is an important constituent of the atmosphere where SOA particles are formed chiefly by the condensation or reactive uptake of oxidation products of volatile organic compounds (VOCs). The mass yield in SOA particle formation, as well as the chemical composition and volatility of the particles, is determined by the identity of the VOC precursor(s) and the oxidation conditions they experience. In this study, we used an oxidation flow reactor to generate biogenic SOA from the oxidation of Scots pine emissions. Mass yields, chemical composition and volatility of the SOA particles were characterized and compared with SOA particles formed from oxidation of α-pinene and from a mixture of acyclic–monocyclic sesquiterpenes (farnesenes and bisabolenes), which are significant components of the Scots pine emissions. SOA mass yields for Scots pine emissions dominated by farnesenes were lower than for α-pinene but higher than for the artificial mixture of farnesenes and bisabolenes. The reduction in the SOA yield in the farnesene- and bisabolene-dominated mixtures is due to exocyclic C=C bond scission in these acyclic–monocyclic sesquiterpenes during ozonolysis leading to smaller and generally more volatile products. SOA particles from the oxidation of Scots pine emissions had similar or lower volatility than SOA particles formed from either a single precursor or a simple mixture of VOCs. Applying physical stress to the Scots pine plants increased their monoterpene, especially monocyclic β-phellandrene, emissions, which further decreased SOA particle volatility and increased SOA mass yield. Our results highlight the need to account for the chemical complexity and structure of real-world biogenic VOC emissions and stress-induced changes to plant emissions when modelling SOA production and properties in the atmosphere. These results emphasize that a simple increase or decrease in relative monoterpene and sesquiterpene emissions should not be used as an indicator of SOA particle volatility.
Publisher: Copernicus GmbH
Date: 02-01-2019
Abstract: Abstract. The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced a-pinene SOA with three different oxidation levels (characterised by average oxygen to carbon ratio, O : C = 0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH
Publisher: American Geophysical Union (AGU)
Date: 03-07-2021
DOI: 10.1029/2021GL093465
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 (SO 2 ). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO 2 , 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.
Publisher: Copernicus GmbH
Date: 22-10-2019
Publisher: Copernicus GmbH
Date: 02-04-2019
Abstract: Abstract. The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced α-pinene SOA with three different oxidation levels (characterized by average oxygen-to-carbon ratio O:C‾=0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH %, 40 %, and 80 %) and used a filter-based thermal desorption method to gain volatility and chemical composition information. We observed reduced particle evaporation for particles with increasing O:C‾ ratio, indicating that particles become more resilient to evaporation with oxidative aging. Particle evaporation was increased in the presence of water vapour and presumably particulate water at the same time the resistance of the residual particles to thermal desorption was increased as well. For SOA with O:C‾=0.96, the unexpectedly large increase in mean thermal desorption temperature and changes in the thermogram shapes under wet conditions (80 % RH) were an indication of aqueous phase chemistry. For the lower O:C‾ cases, some water-induced composition changes were observed. However, the enhanced evaporation under wet conditions could be explained by the reduction in particle viscosity from the semi-solid to liquid-like range, and the observed higher desorption temperature of the residual particles is a direct consequence of the increased removal of high-volatility and the continued presence of low-volatility compounds.
Publisher: Springer Science and Business Media LLC
Date: 14-05-2022
DOI: 10.1007/S40279-022-01682-3
Abstract: Research has shown the effectiveness of sedentary behaviour interventions on reducing sedentary time. However, no systematic review has studied where the reduced sedentary time after such interventions is displaced to. Our objective was to synthesize the evidence from interventions that have reduced sedentary behaviour and test the displacement of sedentary time into physical activity (light physical activity [LPA], moderate-to-vigorous physical activity [MVPA], standing, and stepping). Two independent researchers performed a systematic search of the EBSCOhost, PubMed, Scopus, and Web of Science electronic databases. Meta-analyses were performed to examine the time reallocated from sedentary behaviour to physical activity during working time and the whole day in intervention trials (randomized/non-randomized controlled/non-controlled). A total of 36 studies met all the eligibility criteria and were included in the systematic review, with 26 studies included in the meta-analysis. Interventions showed a significant overall increase in worksite LPA (effect size [ES] 0.24 95% confidence interval [CI] 0.05 to 0.43 P < 0.013) and daily LPA (ES 0.62 95% CI 0.34 to 0.91 P = 0.001). A statistically significant increase in daily MVPA was observed (ES 0.47 95% CI 0.26 to 0.67 P < 0.001). There was a significant overall increase in worksite standing time (ES 0.76 95% CI 0.56 to 0.95 P < 0.001), daily standing time (ES 0.52 95% CI 0.38 to 0.65 P < 0.001), and worksite stepping time (ES 0.12 95% CI 0.04 to 0.20 P = 0.002). Effective interventions aimed at reducing sedentary behaviour result in a consistent displacement of sedentary time to LPA and standing time, both at worksites and across the whole day, whereas changes in stepping time or MVPA are dependent on the intervention setting. Strategies to reduce sedentary behaviour should not be limited to worksite settings, and further efforts may be required to promote daily MVPA. PROSPERO registration number CRD42020153958.
Publisher: Copernicus GmbH
Date: 22-10-2019
DOI: 10.5194/ACP-2019-939
Abstract: Abstract. Secondary organic aerosol (SOA) is an important constituent of the atmosphere where SOA particles are formed chiefly by the condensation or reactive uptake of oxidation products of volatile organic compounds (VOC). The mass yield in SOA particle formation, as well as the chemical composition and volatility of the particles are determined by the identity of the VOC precursor(s) and the oxidation conditions they experience. In this study, we used an oxidation flow reactor to generate biogenic SOA from the oxidation of Scots pine emissions. Mass yields, chemical composition, and volatility of the SOA particles were characterized and compared with SOA particles formed from oxidation of α-pinene and of a mixture of acyclic/monocyclic sesquiterpenes (farnesenes and bisabolenes), which are significant components of the Scots pine emissions. SOA mass yields for Scots pine emissions dominated by farnesenes were lower than for α-pinene, but higher than for the artificial mixture of farnesenes and bisabolenes. The reduction in the SOA yield in the farnesenes and bisabolenes dominated mixtures is due to C=C bond scission in these acyclic/monocyclic sesquiterpenes during ozonolysis leading to smaller and generally more volatile products. SOA particles from the oxidation of Scots pine emission had similar or lower volatility than SOA particles formed from either of single precursor. Applying physical stress to the Scots pine plants increased monoterpene emissions, which further decreased SOA particle volatility and increased SOA mass yield. Our results highlight the need to account for the chemical complexity and structure of real-world biogenic VOC emissions and stress-induced changes to plant emissions when modelling SOA production and properties in the atmosphere. These results emphasize that simple increase or decrease of relative monoterpene and sesquiterpene emissions should not be used as indicator of SOA particle volatility.
Publisher: Proceedings of the National Academy of Sciences
Date: 03-04-2023
Abstract: Hydroxyl radical (OH) is a key oxidant that triggers atmospheric oxidation chemistry in both gas and aqueous phases. The current understanding of its aqueous sources is mainly based on known bulk (photo)chemical processes, uptake from gaseous OH, or related to interfacial O 3 and NO 3 radical-driven chemistry. Here, we present experimental evidence that OH radicals are spontaneously produced at the air–water interface of aqueous droplets in the dark and the absence of known precursors, possibly due to the strong electric field that forms at such interfaces. The measured OH production rates in atmospherically relevant droplets are comparable to or significantly higher than those from known aqueous bulk sources, especially in the dark. As aqueous droplets are ubiquitous in the troposphere, this interfacial source of OH radicals should significantly impact atmospheric multiphase oxidation chemistry, with substantial implications on air quality, climate, and health.
Location: United States of America
No related grants have been discovered for Sergey Nizkorodov.