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

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.

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

Atmospheric Environment ◽

10.1016/j.atmosenv.2021.118738 ◽

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

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Characterization of aerosol and cloud water at a mountain site during WACS 2010: secondary organic aerosol formation through oxidative cloud processing

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-6019-2012 ◽

2012 ◽

Vol 12 (2) ◽

pp. 6019-6047 ◽

Cited By ~ 3

Author(s):

A. K. Y. Lee ◽

K. L. Hayden ◽

P. Herckes ◽

W. R. Leaitch ◽

J. Liggio ◽

...

Keyword(s):

Aqueous Phase ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Cloud Water ◽

Water Soluble ◽

Photochemical Oxidation ◽

Aerosol Formation ◽

Aerosol Mass ◽

Dissolved Organics ◽

Organic Spectra

Abstract. The water-soluble fractions of aerosol samples and cloud water collected during Whistler Aerosol and Cloud Study (WACS 2010) were analyzed using an Aerodyne aerosol mass spectrometer (AMS). This is the first study to report AMS organic spectra of re-aerosolized cloud water, and to make direct comparison between the AMS spectra of cloud water and aerosol samples collected at the same location. In general, the aerosol and cloud organic spectra were very similar, indicating that the cloud water organics likely originated from secondary organic aerosol (SOA) formed nearby. By using a photochemical reactor to oxidize both aerosol filter extracts and cloud water, we find evidence that fragmentation of aerosol water-soluble organics increases their volatility during oxidation. By contrast, enhancement of AMS-measurable organic mass by up to 30% was observed during aqueous-phase photochemical oxidation of cloud water organics. We propose that additional SOA material was produced by functionalizing dissolved organics via OH oxidation, where these dissolved organics are sufficiently volatile that they are not usually part of the aerosol. This work points out that water-soluble organic compounds of intermediate volatility (IVOC), such as cis-pinonic acid, produced via gas-phase oxidation of monoterpenes, can be important aqueous-phase SOA precursors in a biogenic-rich environment.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-2871-2014 ◽

2014 ◽

Vol 14 (6) ◽

pp. 2871-2885 ◽

Cited By ~ 45

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.

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Characterization of Products from the Aqueous-Phase Photochemical Oxidation of Benzene-Diols

Atmosphere ◽

10.3390/atmos12050534 ◽

2021 ◽

Vol 12 (5) ◽

pp. 534

Author(s):

Yang Ou ◽

Dongyang Nie ◽

Hui Chen ◽

Zhaolian Ye ◽

Xinlei Ge

Keyword(s):

Aqueous Phase ◽

Irradiation Time ◽

Chemical Properties ◽

Oxidation Products ◽

Photochemical Oxidation ◽

Reaction Products ◽

Reaction Conditions ◽

Oxidative Potential ◽

Photo Degradation

Chemical processing in atmospheric aqueous phases, including cloud and fog drops, might be significant in reconciling the gap between observed and modeled secondary organic aerosol (SOA) properties. In this work, we conducted a relatively comprehensive investigation of the reaction products generated from the aqueous-phase photochemical oxidation of three benzene-diols (resorcinol, hydroquinone, and methoxyhydroquinone) by hydroxyl radical (·OH), triplet excited state (3C*) 3,4-dimethoxybenzaldehyde (3,4-DMB), and direct photolysis without any added oxidants. The results show that OH-initiated photo-degradation is the fastest of all the reaction systems. For the optical properties, the aqueous oxidation products generated under different reaction conditions all exhibited photo-enhancement upon illumination by simulated sunlight, and the light absorption was wavelength dependent on and increased as a function of the reaction time. The oxygen-to-carbon (O/C) ratio of the products also gradually increased against the irradiation time, indicating the persistent formation of highly oxygenated low-volatility products throughout the aging process. More importantly, aqueous-phase products from photochemical oxidation had an increased oxidative potential (OP) compared with its precursor, indicating they may more adversely impact health. The findings in this work highlight the importance of aqueous-phase photochemical oxidation, with implications for aqueous SOA formation and impacts on both the chemical properties and health effects of OA.

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Formation of low molecular weight mono- and di-carboxylic acids and related compounds from photochemical oxidation of stearic and linoleic acids in aqueous-phase

10.5194/egusphere-egu2020-20887 ◽

2020 ◽

Author(s):

Chandra Mouli Pavuluri ◽

Subba Rao Devineni ◽

Zhanjie Xu ◽

Kimitaka Kawamura ◽

Pingqing Fu ◽

...

Keyword(s):

Fatty Acids ◽

Aqueous Phase ◽

Cloud Condensation Nuclei ◽

Oxidation Products ◽

Photochemical Oxidation ◽

Air Water Interface ◽

Volatile Organic ◽

Product Species ◽

Related Compounds ◽

Atmospheric Waters

Secondary organic aerosols (SOA) that account for a substantial and often a dominant fraction of total OA mass are formed by photooxidation of various precursors derived from anthropogenic and biogenic sources in the atmosphere. They have serious impacts on the Earth&#8217;s climate system directly by scattering and absorbing solar radiation and indirectly by acting as cloud condensation nuclei, and adverse effects on human health. In recent times, considerable attention has been paid on laboratory studies, preferably in gas-phase, in order to understand the chemistry of SOA formation. However, the studies on SOA formation in aqueous phase are limited, which are mainly focused on high abundant volatile organic compounds (e.g., isoprene) and/or their oxidation products, but not on fatty acids (except oleic acid). To better understand the air-water interface photochemistry of fatty acids and their transformations to lower homologous monoacids and more oxygenated species such as diacids and related compounds in atmospheric waters (fog, cloud and aqueous aerosol), we conducted batch UV irradiation experiments on a saturated (stearic acid, C18H36O2) and an unsaturated (linoleic acid, C18H32O2) fatty acids for different time periods (age, 0-120 h) in aqueous-phase. All the irradiated samples were analyzed for measurements of mono- and di-acids, oxoacids and &#945;-dicarbonyls. We found high abundances of monoacids followed by diacids, pyruvic acid and &#945;-dicarbonyls in less aged samples, whereas C3&#160;and C4&#160;diacids were abundant in the more aged samples. Our results imply that the photochemical oxidation of fatty acids and subsequent transformations of the product species in atmospheric waters are significant and their contribution to more oxygenated SOA is increased with aging in the atmosphere.

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Characteristics, primary sources and secondary formation of water-soluble organic aerosols in downtown Beijing

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-1775-2021 ◽

2021 ◽

Vol 21 (3) ◽

pp. 1775-1796

Author(s):

Qing Yu ◽

Jing Chen ◽

Weihua Qin ◽

Siming Cheng ◽

Yuepeng Zhang ◽

...

Keyword(s):

Organic Carbon ◽

Aqueous Phase ◽

Critical Role ◽

Organic Aerosols ◽

Sampling Period ◽

Water Soluble ◽

Photochemical Oxidation ◽

Primary Sources ◽

Secondary Formation ◽

The Impact

Abstract. Water-soluble organic carbon (WSOC) accounts for a large proportion of aerosols and plays a critical role in various atmospheric chemical processes. In order to investigate the primary sources and secondary production of WSOC in downtown Beijing, day and night fine particulate matter (PM2.5) samples in January (winter), April (spring), July (summer) and October (autumn) 2017 were collected and analyzed for WSOC and organic tracers in this study. WSOC was dominated by its moderately hydrophilic fraction and showed the highest concentration in January and comparable levels in April, July and October 2017. Some typical organic tracers were chosen to evaluate the emission strength and secondary formation of WSOC. Seasonal variation of the organic tracers suggested significantly enhanced formation of anthropogenic secondary organic aerosols (SOAs) during the sampling period in winter and obviously elevated biogenic SOA formation during the sampling period in summer. These organic tracers were applied into a positive matrix factorization (PMF) model to calculate the source contributions of WSOC as well as its moderately and strongly hydrophilic portions. The secondary sources contributed more than 50 % to WSOC, with higher contributions during the sampling periods in summer (75.1 %) and winter (67.4 %), and the largest contributor was aromatic SOC. In addition, source apportionment results under different pollution levels suggested that controlling biomass burning and aromatic precursors would be effective to reduce WSOC during the haze episodes in cold seasons. The impact factors for the formation of different SOA tracers and total secondary organic carbon (SOC) as well as moderately and strongly hydrophilic SOC were also investigated. The acid-catalyzed heterogeneous or aqueous-phase oxidation appeared to dominate in the SOC formation during the sampling period in winter, while the photochemical oxidation played a more critical role during the sampling period in summer. Moreover, photooxidation played a more critical role in the formation of moderately hydrophilic SOC, while the heterogeneous or aqueous-phase reactions had more vital effects on the formation of strongly hydrophilic SOC.

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Photochemical oxidation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in aqueous phase

Safety and Security Engineering III ◽

10.2495/safe090101 ◽

2009 ◽

Author(s):

S. M. Celin ◽

M. Pandit ◽

J. C. Kapoor

Keyword(s):

Aqueous Phase ◽

Photochemical Oxidation

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Distinctions in source regions and formation mechanisms of secondary aerosol in Beijing from summer to winter

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-10319-2019 ◽

2019 ◽

Vol 19 (15) ◽

pp. 10319-10334 ◽

Cited By ~ 17

Author(s):

Jing Duan ◽

Ru-Jin Huang ◽

Chunshui Lin ◽

Wenting Dai ◽

Meng Wang ◽

...

Keyword(s):

Chemical Composition ◽

Aqueous Phase ◽

Regional Scale ◽

Late Summer ◽

Photochemical Oxidation ◽

Formation Mechanisms ◽

Early Winter ◽

Secondary Aerosol ◽

Haze Pollution ◽

Sulfate Formation

Abstract. To investigate the sources and evolution of haze pollution in different seasons, long-term (from 15 August to 4 December 2015) variations in chemical composition of PM1 were characterized in Beijing, China. Positive matrix factorization (PMF) analysis with a multi-linear engine (ME-2) resolved three primary and two secondary organic aerosol (OA) sources, including hydrocarbon-like OA (HOA), cooking OA (COA), coal combustion OA (CCOA), local secondary OA (LSOA) and regional SOA (RSOA). The sulfate source region analysis implies that sulfate was mainly transported at a large regional scale in late summer, while local and/or nearby sulfate formation may be more important in winter. Meanwhile, distinctly different correlations between sulfate and RSOA or LSOA (i.e., better correlation with RSOA in late summer, similar correlations with RSOA and LSOA in autumn, and close correlation with LSOA in early winter) confirmed the regional characteristic of RSOA and local property of LSOA. Secondary aerosol species including secondary inorganic aerosol (SIA – sulfate, nitrate, and ammonium) and SOA (LSOA and RSOA) dominated PM1 during all three seasons. In particular, SOA contributed 46 % to total PM1 (with 31 % as RSOA) in late summer, whereas SIA contributed 41 % and 45 % to total PM1 in autumn and early winter, respectively. Enhanced contributions of secondary species (66 %–76 % of PM1) were also observed in pollution episodes during all three seasons, further emphasizing the importance of secondary formation processes in haze pollution in Beijing. Combining chemical composition and meteorological data, our analyses suggest that both photochemical oxidation and aqueous-phase processing played important roles in SOA formation during all three seasons, while for sulfate formation, gas-phase photochemical oxidation was the major pathway in late summer, aqueous-phase reactions were more responsible during early winter and both processes had contributions during autumn.

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Summertime and wintertime atmospheric processes of secondary aerosol in Beijing

10.5194/egusphere-egu2020-7440 ◽

2020 ◽

Author(s):

Jing Duan ◽

Rujin Huang ◽

Chunshui Lin ◽

Haiyan Ni ◽

Meng Wang

Keyword(s):

Aqueous Phase ◽

Liquid Water ◽

Fine Particles ◽

Photochemical Oxidation ◽

Formation Mechanisms ◽

Phase Reaction ◽

Aerosol Formation ◽

Secondary Aerosol ◽

Atmospheric Processes ◽

Sulfate Formation

Secondary aerosol constitutes a large fraction of fine particles in urban air of China. However, its formation mechanisms and atmospheric processes remain largely uncertain despite considerable studies in recent years. To elucidate the seasonal variations of fine particles composition and secondary aerosol formation, an Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM) combined with other online instruments were used to characterize the submicron particulate matter (diameter < 1 &#956;m, PM1) in Beijing during summer and winter 2015. Our results suggest that the photochemical oxidation was the major pathway for sulfate formation during summer, whereas aqueous-phase reaction became an important process for sulfate formation during winter. High concentration of nitrate (17% of the PM1 mass) was found during winter explained by enhanced gas-to-particle partitioning at low temperature, while high nitrate concentration (19%) was also observed under the conditions of high relative humidity (RH) during summer likely due to the hydrophilic property of NH4NO3 and hydrolysis of N2O5. As for SOA formation, photochemical oxidation perhaps played an important role for summertime oxygenated OA (OOA) formation and wintertime less oxidized OOA (LO-OOA) formation. The wintertime more oxidized OOA (MO-OOA) showed a good correlation with aerosol liquid water content (ALWC), indicating more important contribution of aqueous-phase processing than photochemical production to MO-OOA. Meanwhile, the dependence of LO-OOA and the mass ratio of LO-OOA to MO-OOA on atmospheric oxidative tracer (i.e., Ox) both degraded when RH were greater than 60%, suggesting that RH or aerosol liquid water may also affect the LO-OOA formation.

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