scholarly journals Aqueous-phase photochemical oxidation and direct photolysis of vanillin – a model compound of methoxy-phenols from biomass burning

2013 ◽  
Vol 13 (10) ◽  
pp. 27641-27675
Author(s):  
Y. J. Li ◽  
D. D. Huang ◽  
H. Y. Cheung ◽  
A. K. Y. Lee ◽  
C. K. Chan
Keyword(s):  
Aqueous Phase ◽  
Biomass Burning ◽  
Model Compound ◽  
Photochemical Oxidation ◽  
Particle Phase ◽  
Organic Mass ◽  
Direct Photolysis ◽  
Volatile Products ◽  
Reacting Mixtures ◽  
Condition B

Abstract. We present here experimental results on aqueous-phase (A) photochemical oxidation (with UV and OH radicals generated from H2O2 photolysis) and (B) direct photolysis (with only UV irradiation) of a methoxy-phenol, vanillin (VL), as a model compound from biomass burning. Both on-line aerosol mass spectrometric (AMS) characterization and off-line chemical analyses were performed. AMS analyses of dried atomized droplets of the bulk reacting mixtures showed that VL almost entirely evaporates during the drying process. Large amounts of organic mass remained in the particle phase after reactions under both conditions. Under condition (A), AMS measured organic mass first increased rapidly and then decreased, attributable to the formation of non-volatile products and subsequent formation of smaller and volatile products, respectively. The oxygen-to-carbon (O:C) ratio of the products reached 1.5 after about 80 min, but dropped substantially thereafter. In contrast, organic mass increased slowly under condition (B). The O:C ratio reached 1.0 after 180 min. In off-line analyses, small oxygenates were detected under condition (A), while hydroxylated products and dimers of VL were detected under condition (B). Particle hygroscopic growth factor (GF) and cloud condensation nuclei (CCN) activity of the reacting mixtures were found to be dependent on both organic volume fraction and the degree of oxygenation of organics. Results show that (1) aqueous-phase processes can lead to the retention of a large portion of the organic mass in the particle phase; (2) once retained, this portion of organic mass significantly changes the hygroscopicity and CCN activity of the aerosol particles; (3) intensive photochemical oxidation gave rise to an O:C ratio as high as 1.5 but the ratio decreased as further oxidation led to smaller and more volatile products; and (4) polymerization occurred with direct photolysis, resulting in high-molecular-weight products of a yellowish color. This study demonstrates that aqueous-phase reactions of a methoxy-phenol can lead to substantial amount of secondary organic aerosol (SOA) formation. Given the vast amount of biomass burning input globally, model representation of either the SOA budget or their subsequent effects would not be adequate if the contribution of SOA formation from aqueous-phase reactions of methoxy-phenols is not considered.

scholarly journals Aqueous-phase photochemical oxidation and direct photolysis of vanillin – a model compound of methoxy phenols from biomass burning

2014 ◽  
Vol 14 (6) ◽  
pp. 2871-2885 ◽  
Author(s):  
Y. J. Li ◽  
D. D. Huang ◽  
H. Y. Cheung ◽  
A. K. Y. Lee ◽  
C. K. Chan
Keyword(s):  
Aqueous Phase ◽  
Biomass Burning ◽  
Model Compound ◽  
Photochemical Oxidation ◽  
Particle Phase ◽  
Organic Mass ◽  
Direct Photolysis ◽  
Volatile Products ◽  
Reacting Mixtures ◽  
Condition B

Abstract. We present here experimental results on aqueous-phase (A) photochemical oxidation (with UV and OH radicals generated from H2O2 photolysis) and (B) direct photolysis (with only UV irradiation) of a methoxy phenol, vanillin (VL), as a model compound from biomass burning. Both on-line aerosol mass spectrometric (AMS) characterization and off-line chemical analyses were performed. AMS analyses of dried atomized droplets of the bulk reacting mixtures showed that VL almost entirely evaporates during the drying process. Large amounts of organic mass remained in the particle phase after reactions under both conditions. Under condition (A), AMS measured organic mass first increased rapidly and then decreased, attributable to the formation of non-volatile products and subsequent formation of smaller and volatile products, respectively. The oxygen-to-carbon (O : C) ratio of the products reached 1.5 after about 80 min, but dropped substantially thereafter. In contrast, organic mass increased slowly under condition (B). The O : C ratio reached 1.0 after 180 min. In off-line analyses, small oxygenates were detected under condition (A), while hydroxylated products and dimers of VL were detected under condition (B). Particle hygroscopic growth factor (GF) and cloud condensation nuclei (CCN) activity of the reacting mixtures were found to depend on both organic volume fraction and the degree of oxygenation of organics. Results show that (1) aqueous-phase processes can lead to the retention of a large portion of the organic mass in the particle phase; (2) once retained, this portion of organic mass significantly changes the hygroscopicity and CCN activity of the aerosol particles; (3) intensive photochemical oxidation gave rise to an O : C ratio as high as 1.5 but the ratio decreased as further oxidation led to smaller and more volatile products; and (4) polymerization occurred with direct photolysis, resulting in high-molecular-weight products of a yellowish color. This study demonstrates that aqueous-phase reactions of a methoxy phenol can lead to substantial amount of secondary organic aerosol (SOA) formation. Given the vast amount of biomass burning input globally, model representation of either the SOA budget or their subsequent effects would not be adequate if the contribution of SOA formation from aqueous-phase reactions of methoxy phenols is not considered.

Photosensitization by Cd 3P1 atoms. I. Decomposition of acetone

1970 ◽  
Vol 48 (8) ◽  
pp. 1333-1334 ◽  
Author(s):  
B. L. Kalra ◽  
A. R. Knight
Keyword(s):  
Acetone Vapor ◽  
Direct Photolysis ◽  
Virtual Identity ◽  
Excited Species ◽  
Volatile Products ◽  
Acetone System

The photodecomposition of acetone vapor at 255 °C sensitized by Cd 3P1 atoms has been investigated. On irradiation of the Cd–acetone system at 3261 Å, both direct and sensitized reaction occur. CO and CH4 are the only significant volatile products, and their yield is decreased by addition of SF6 as inert quenching gas. The required participation of triplet acetone molecules in the sensitized reaction and the virtual identity of the direct and sensitized decompositions provide additional evidence for the importance of this excited species in direct photolysis.

The Roles of Aqueous-Phase Chemistry and Photochemical Oxidation in Oxygenated Organic Aerosols Formation

2021 ◽  
pp. 118738
Author(s):  
Bixin Zhan ◽  
Haobin Zhong ◽  
Hui Chen ◽  
Yunqian Chen ◽  
Xiang Li ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Organic Aerosols ◽  
Photochemical Oxidation ◽  
Phase Chemistry

Modelling the Tropospheric Multiphase Chemistry of Biomass Burning Trace Compounds Using the Chemical Aqueous Phase Radical Mechanism (CAPRAM)

2021 ◽  
Author(s):  
Lin He ◽  
Erik Hans Hoffmann ◽  
Andreas Tilgner ◽  
Hartmut Herrmann
Keyword(s):  
Aqueous Phase ◽  
Biomass Burning ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Radical Mechanism ◽  
Aerosol Formation ◽  
Detailed Model ◽  
Model Studies ◽  
Trace Species

<p>Biomass burning (BB) is a significant contributor to air pollution on global, regional and local scale with impacts on air quality, public health and climate. Anhydrosugars (levoglucosan, mannosan and galactocan) and methoxyphenols (guaiacol, creosol, etc.) are important tracer compounds emitted through biomass burning. Once emitted, they can undergo complex multiphase chemistry in the atmosphere contributing to secondary organic aerosol formation. However, their chemical multiphase processing is not yet well understood and investigated by models. Therefore, the present study aimed at a better understanding of the multiphase chemistry of these BB trace species by means of detailed model studies with a new developed detailed chemical CAPRAM biomass burning module (CAPRAM-BB). This module was developed based on the kinetic data from the laser flash photolysis measurements in our lab at TROPOS and other literature studies. The developed CAPRAM-BB module includes 2991 reactions (thereof 9 phase transfers and 2982 aqueous-phase reactions). By coupling with the multiphase chemistry mechanism MCMv3.2/CAPRAM4.0 and the extended CAPRAM aromatics (CAPRAM-AM1.0) and halogen modules (CAPRAM-HM3.0), it is being applied for some residential wood burning cases in Europe and wildfire cases in the US. Our model results show that the BB chemistry could significantly affect the budgets of important atmospheric oxidants such as H<sub>2</sub>O<sub>2</sub> and HONO, and contribute to the SOA formation especially the fraction of brown carbon and substituted organic acids.</p>

A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol

2019 ◽  
Vol 685 ◽  
pp. 976-985 ◽  
Author(s):  
Zhaolian Ye ◽  
Zhenxiu Qu ◽  
Shuaishuai Ma ◽  
Shipeng Luo ◽  
Yantong Chen ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Photochemical Oxidation ◽  
Comprehensive Investigation

scholarly journals Composition and light absorption of nitroaromatic compounds in organic aerosols from laboratory biomass burning

2018 ◽  
Author(s):  
Mingjie Xie ◽  
Xi Chen ◽  
Michael D. Hays ◽  
Amara L. Holder
Keyword(s):  
Experimental Data ◽  
Biomass Burning ◽  
Organic Aerosols ◽  
Chemical Properties ◽  
Nitroaromatic Compounds ◽  
Forest Understory ◽  
Prescribed Fires ◽  
Organic Mass ◽  
Total Contribution ◽  
Mass Spectral

Abstract. This study seeks to understand the compositional details of nitroaromatic 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 test specific 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 NACs were identified in the BB samples, four of which (C10H11NO4, C10H11NO5, C11H13NO5 and C11H13NO6) have not been observed previously in chamber-based secondary organic aerosols, and are expected to have methoxyphenol-type structure specific to the pyrolized biomass lignin based on mass spectral evidence, suggesting these compounds may be unique to BB aerosols. The average total contribution of NACs to organic mass (0.023 ± 0.0089 to 0.18 ± 0.067 %) was 5–10 times lower than the average contribution to the overall BrC absorption at 365 nm (0.12 ± 0.047 to 2.44 ± 0.67 %). The average contributions (%) of total NACs to organic mass and aqueous extracts absorption correlated significantly (p < 0.05) with EC/OC for both test specific and pooled experimental data. These results suggested that the formation of NACs from BB depended more on burn conditions than the bulk absorptive properties of BB BrC.

scholarly journals Kinetic modeling studies of SOA formation from <i>α</i>-pinene ozonolysis

2017 ◽  
Vol 17 (21) ◽  
pp. 13187-13211 ◽  
Author(s):  
Kathrin Gatzsche ◽  
Yoshiteru Iinuma ◽  
Andreas Tilgner ◽  
Anke Mutzel ◽  
Torsten Berndt ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Organic Compounds ◽  
Diffusion Coefficients ◽  
Bulk Diffusion ◽  
Organic Aerosol ◽  
Successful Implementation ◽  
Particle Phase ◽  
Organic Mass ◽  
Model Framework ◽  
Aerosol Mass Concentration

Abstract. This paper describes the implementation of a kinetic gas-particle partitioning approach used for the simulation of secondary organic aerosol (SOA) formation within the SPectral Aerosol Cloud Chemistry Interaction Model (SPACCIM). The kinetic partitioning considers the diffusion of organic compounds into aerosol particles and the subsequent chemical reactions in the particle phase. The basic kinetic partitioning approach is modified by the implementation of chemical backward reaction of the solute within the particle phase as well as a composition-dependent particle-phase bulk diffusion coefficient. The adapted gas-phase chemistry mechanism for α-pinene oxidation has been updated due to the recent findings related to the formation of highly oxidized multifunctional organic compounds (HOMs). Experimental results from a LEAK (Leipziger Aerosolkammer) chamber study for α-pinene ozonolysis were compared with the model results describing this reaction system.The performed model studies reveal that the particle-phase bulk diffusion coefficient and the particle-phase reactivity are key parameters for SOA formation. Using the same particle-phase reactivity for both cases, we find that liquid particles with higher particle-phase bulk diffusion coefficients have 310 times more organic material formed in the particle phase compared to higher viscous semi-solid particles with lower particle-phase bulk diffusion coefficients. The model results demonstrate that, even with a moderate particle-phase reactivity, about 61 % of the modeled organic mass consists of reaction products that are formed in the liquid particles. This finding emphasizes the potential role of SOA processing. Moreover, the initial organic aerosol mass concentration and the particle radius are of minor importance for the process of SOA formation in liquid particles. A sensitivity study shows that a 22-fold increase in particle size merely leads to a SOA increase of less than 10 %.Due to two additional implementations, allowing backward reactions in the particle phase and considering a composition-dependent particle-phase bulk diffusion coefficient, the potential overprediction of the SOA mass with the basic kinetic approach is reduced by about 40 %. HOMs are an important compound group in the early stage of SOA formation because they contribute up to 65 % of the total SOA mass at this stage. HOMs also induce further SOA formation by providing an absorptive medium for SVOCs (semi-volatile organic compounds). This process contributes about 27 % of the total organic mass. The model results are very similar to the LEAK chamber results. Overall, the sensitivity studies demonstrate that the particle reactivity and the particle-phase bulk diffusion require a better characterization in order to improve the current model implementations and to validate the assumptions made from the chamber simulations. The successful implementation and testing of the current kinetic gas-particle partitioning approach in a box model framework will allow further applications in a 3-D model for regional-scale process investigations.

The changing nature of particulate organic carbon and the relation to aerosol liquid water

2020 ◽  
Author(s):  
Annmarie Carlton ◽  
Amy Christiansen ◽  
William Porter ◽  
Madison Flesch
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Liquid Water ◽  
Phase State ◽  
Monitoring Network ◽  
Particle Phase ◽  
Organic Mass ◽  
West Texas ◽  
Isoprene Oxidation ◽  
Mass Concentrations

&lt;p&gt;Particulate organic carbon (OC) mass concentrations demonstrate decreasing trends in many regions across the contiguous US (CONUS). We investigate decadal trends in specific total organic carbon (TOC) volatility fractions OC1, OC2, OC3, and OC4 as defined and reported at 121 locations in the Interagency Monitoring of PROtected Visual Environments (IMPROVE) monitoring network from 2005-2016 for 23 chemical climatology regions across the CONUS. Volatility fraction OC2 drives ubiquitous decadal decreases in TOC, and OC3 mass concentrations increase. The largest changes in OC2 and OC3 occur in the eastern US. In four focus regions (Northeast, Appalachia, West Texas, and Northwest), OC fraction mass concentrations are converted to organic mass (OM) using region-specific OM:OC ratios. GEOS-Chem simulations reproduce and correlate strongly (R&lt;sup&gt;2&lt;/sup&gt;&gt;0.7) with OM fraction decadal trends. Decreases in aerosol liquid water (ALW) concentrations are tightly linked to observed change in individual TOC thermal fractions, and aerosol products derived from aqueous-phase isoprene oxidation predicted by GEOS-Chem. These results lend insight to changing chemical regimes with implications for particle phase state, viscosity, and oxidation state.&lt;/p&gt;

scholarly journals Secondary organic aerosol formation in biomass-burning plumes: theoretical analysis of lab studies and ambient plumes

2017 ◽  
Vol 17 (8) ◽  
pp. 5459-5475 ◽  
Author(s):  
Qijing Bian ◽  
Shantanu H. Jathar ◽  
John K. Kodros ◽  
Kelley C. Barsanti ◽  
Lindsay E. Hatch ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Smog Chamber ◽  
Particle Phase ◽  
Wall Losses ◽  
Wall Loss ◽  
The Mean ◽  
Mass Enhancement ◽  
Fire Conditions

Abstract. Secondary organic aerosol (SOA) has been shown to form in biomass-burning emissions in laboratory and field studies. However, there is significant variability among studies in mass enhancement, which could be due to differences in fuels, fire conditions, dilution, and/or limitations of laboratory experiments and observations. This study focuses on understanding processes affecting biomass-burning SOA formation in laboratory smog-chamber experiments and in ambient plumes. Vapor wall losses have been demonstrated to be an important factor that can suppress SOA formation in laboratory studies of traditional SOA precursors; however, impacts of vapor wall losses on biomass-burning SOA have not yet been investigated. We use an aerosol-microphysical model that includes representations of volatility and oxidation chemistry to estimate the influence of vapor wall loss on SOA formation observed in the FLAME III smog-chamber studies. Our simulations with base-case assumptions for chemistry and wall loss predict a mean OA mass enhancement (the ratio of final to initial OA mass, corrected for particle-phase wall losses) of 1.8 across all experiments when vapor wall losses are modeled, roughly matching the mean observed enhancement during FLAME III. The mean OA enhancement increases to over 3 when vapor wall losses are turned off, implying that vapor wall losses reduce the apparent SOA formation. We find that this decrease in the apparent SOA formation due to vapor wall losses is robust across the ranges of uncertainties in the key model assumptions for wall-loss and mass-transfer coefficients and chemical mechanisms.We then apply similar assumptions regarding SOA formation chemistry and physics to smoke emitted into the atmosphere. In ambient plumes, the plume dilution rate impacts the organic partitioning between the gas and particle phases, which may impact the potential for SOA to form as well as the rate of SOA formation. We add Gaussian dispersion to our aerosol-microphysical model to estimate how SOA formation may vary under different ambient-plume conditions (e.g., fire size, emission mass flux, atmospheric stability). Smoke from small fires, such as typical prescribed burns, dilutes rapidly, which drives evaporation of organic vapor from the particle phase, leading to more effective SOA formation. Emissions from large fires, such as intense wildfires, dilute slowly, suppressing OA evaporation and subsequent SOA formation in the near field. We also demonstrate that different approaches to the calculation of OA enhancement in ambient plumes can lead to different conclusions regarding SOA formation. OA mass enhancement ratios of around 1 calculated using an inert tracer, such as black carbon or CO, have traditionally been interpreted as exhibiting little or no SOA formation; however, we show that SOA formation may have greatly contributed to the mass in these plumes.In comparison of laboratory and plume results, the possible inconsistency of OA enhancement between them could be in part attributed to the effect of chamber walls and plume dilution. Our results highlight that laboratory and field experiments that focus on the fuel and fire conditions also need to consider the effects of plume dilution or vapor losses to walls.

Photolysis and Photocatalysis of 1,4 Dichlorobenzene Using Sputtered TiO2 Thin Films

2012 ◽  
Vol 734 ◽  
pp. 215-225 ◽  
Author(s):  
Sawsan A. Mahmoud ◽  
Emre Yassitepe ◽  
S. Ismat Shah
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Aqueous Phase ◽  
Wavelength Range ◽  
Photoelectron Spectroscopy ◽  
X Ray Diffraction ◽  
Direct Photolysis ◽  
X Ray ◽  
Degradation Rates ◽  
Visible Irradiation

The rate of 1,4-dichlorobenzene (1,4-DCB) degradation in the aqueous phase was investigated under direct photolysis or photocatalysis in the presence of TiO2 thin film prepared by reactive sputtering using a metal Ti target and a reaction sputtering atmosphere of argon and oxygen. The prepared thin films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS confirmed the presence of completely oxidized TiO2 films whereas XRD showed that the films contained a mixture of rutile and anatase phases with rutile being approximately 30% of the total volume. Two lamps, both of the same power but different wavelength range were employed as irradiation sources. Photocatalysis showed faster removal of 1,4-DCB as compared to direct photolysis. The complete degradation was attained using the freshly prepared TiO2 sample. The intermediate produced during the photocatalysis was benzoquinone. Photolysis using visible irradiation was relatively slower and both benzoquinone and hydroquinone were formed as intermediates. Higher initial degradation rates were observed when the same film was re-used, most probably due to the effect of washing of the TiO2 thin films surface with methanol.

Sign in / Sign up

Export Citation Format

Share Document