Methoxyphenols, which are emitted through biomass burning, are an important species in atmospheric chemistry. In the present study, temperature-dependent aqueous-phase OH radical reactions of six ...methoxyphenols and two related phenols have been investigated through laser flash photolysis and the density functional theory. The rate constants obtained were in a range of (1.1–1.9) × 1010 L mol–1 s–1 with k(3-MC) > k(Cre) ≈ k(Syr) ≈ k(MEP) > k(Res) > k(3-MP) > k(2-EP) ≈ k(2-MP). We derived the parameters of these reactions from the obtained T-dependent rate constants and found a mean Arrhenius activation energy of 16.9 kJ mol–1. The diffusion rate constants were calculated for each case and compared to the measured ones. Generally, the rate constants are found to be close to fully diffusion-controlled (k diff = (1.4–1.5) × 1010 L mol–1 s–1 for all reactions). A structure–function relationship was established through the measurement result, which could be used for predicting unknown rate constants of other phenolic compounds. All of these findings are expected to enhance the predictive capabilities of models, such as the chemical aqueous-phase radical mechanism.
Our current understanding of the importance of surface-active substances (SAS) on atmospheric aerosol cloud-forming efficiency is limited, as explicit data on the content of size-resolved ambient ...aerosol SAS, which are responsible for lowering the surface tension (σ) of activating droplets, are not available. We report on the first data comprising seasonal variability of size-segregated SAS concentrations in ambient aerosol particulate matter (PM). To assess the impact of SAS distribution within PM on cloud droplet activation and growth, a concept of surfactant activity was adopted and a parametrization developed; i.e., surfactant activity factor (SAF) was defined, which allowed translation of experimental data for use in cloud parcel modeling. The results show that SAS-induced σ depression during cloud activation may affect droplet number (N d) as much as a 2-fold increase in particle number, whereas by considering also the size distribution of particulate SAS, N d may increase for another 10%. This study underscores the importance of size-resolved SAS perspective on cloud activation, as data typically obtained from aqueous extracts of PM2.5 and PM10 may result in misleading conclusions about droplet growth due to large mass fractions of supermicron particles with SAS deficit and little or no influence on CCN and N d.
Many ambiguities surround the possible mechanisms of colored and toxic nitrophenols formation in natural systems. Nitration of a biologically and environmentally relevant aromatic compound, guaiacol ...(2-methoxyphenol), under mild aqueous-phase conditions (ambient temperatures, pH 4.5) was investigated by a temperature-dependent experimental modeling coupled to extensive ab initio calculations to obtain the activation energies of the modeled reaction pathways. The importance of dark nonradical reactions is emphasized, involving nitrous (HNO2) and peroxynitrous (HOONO) acids. Oxidation by HOONO is shown to proceed via a nonradical pathway, possibly involving the nitronium ion (NO2 +) formation. Using quantum chemical calculations at the MP2/6-31++g(d,p) level, NO2 • is shown capable of abstracting a hydrogen atom from the phenolic group on the aromatic ring. In a protic solvent, the corresponding aryl radical can combine with HNO2 to yield OH• and, after a subsequent oxidation step, nitrated aromatic products. The demonstrated chemistry is especially important for understanding the aging of nighttime atmospheric deliquesced aerosol. The relevance should be further investigated in the atmospheric gaseous phase. The results of this study have direct implications for accurate modeling of the burden of toxic nitroaromatic pollutants, and the formation of atmospheric brown carbon and its associated influence on Earth’s albedo and climate forcing.
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•The first toxicity data of guaiacol and its nitrated products are presented.•All studied compounds are considered harmful according to the European legislation.•This study revealed ...similar harmful potential of studied compounds to nitrophenols.•No significant joint actions between the four studied compounds were observed.•A synergistic effect between guaiacol and minor unidentified products is suggested.
Guaiacol (2-methoxyphenol) is an important atmospheric pollutant. It is the major component of wood lignin and is essentially emitted to the atmosphere during biomass burning. Its aging in the tropospheric aqueous phase leads to the generation of the following ring-retaining transformation products, also during nighttime: 4-nitroguaiacol, 6-nitroguaiacol, and dinitroguaiacol. This study presents the first toxicological data of guaiacol and its nitro derivatives and reveals their harmful potential for the ecosystem. Applying V. fischeri bioluminescence acute toxicity test, EC50 values range from 16.7 to 103mgL−1 after a 30-min incubation period, which classifies all investigated compounds as ‘harmful’ according to the European legislation. The investigation of environmentally relevant mixtures did not show significant joint actions between the four studied compounds. Therefore, their concentration addition can be considered for ecotoxicological purposes. However, a synergistic effect between guaiacol and a minor unidentified first-generation product of its aqueous-phase aging was observed and should be taken into account when assessing the reaction mixture toxicity. These results stress the need for further toxicological testing, including organisms of different trophic levels, to better evaluate the environmental hazard of guaiacol and especially its nitro derivatives.
The tropospheric aqueous-phase aging of guaiacol (2-methoxyphenol, GUA), a lignocellulosic biomass burning pollutant, is addressed in this work. Pathways of GUA nitration in aqueous solution under ...atmospherically relevant conditions are proposed and critically discussed. The influence of NaNO2 and H2O2, hydroxyl radical scavenger, and sunlight was assessed by an experimental-modeling approach. In the presence of the urban pollutant, nitrite, GUA is preferentially nitrated to yield 4- and 6-nitroguaiacol. After a short lag-time, 4,6-dinitroguaiacol is also formed. Its production accelerates after guaiacol is completely consumed, which is nicely described by the model function accounting for NO2 • and NO2 + as nitrating agents. Although the estimated second-order kinetic rate constants of methoxyphenol nitration with NO2 • are substantially higher than the corresponding rate constants of nitration with NO2 +, nitration rates are competitive under nighttime and liquid atmospheric aerosol-like conditions. In contrast to concentrations of radicals, which are governed by the interplay between diffusion-controlled reactions and are therefore mostly constant, concentrations of electrophiles are very much dependent on the ratio of NO2 – to activated aromatics in solution. These results contribute substantially to the understanding of methoxyphenol aging in the atmospheric waters and underscore the importance of including electrophilic aromatic substitution reactions in atmospheric models.
Covalent adaptable networks (CANs) play an important role in polymer chemistry, as they provide an innovative link between thermoplastics and thermosets. The breakthrough idea behind CANs is to at ...least partially replace irreversible crosslinks in classic thermoset polymers with dynamic covalent bonds that allow for reversible polymer character and recyclability. Besides, CANs also offer other popular features such as self-healing, weldability, configurability, and shape memory. Most CANs are still petroleum-based, yet shifting toward more sustainable approaches is of the utmost interest. Considering this and the high abundance of lignocellulosic biomass, this perspective focuses on all the research found on lignin-based CANs, including both those starting from fractionated lignin and from lignin-based monomers. This is clearly a new branch within bio-based CANs that holds great potential in various industries. Additionally, some examples of thermoset polymers derived from the same lignin building blocks are given to showcase important chemical transformations that can be used for CANs design in the future. Although CAN design has been extended to many different types of bonds, imines and disulfides largely prevail in the current literature. Lastly, a SWOT (strengths, weaknesses, opportunities, and threats) analysis is presented, considering the performance, competition, opportunities, and drawbacks of lignin-derived CANs.
Yellow-colored methylnitrocatechols (MNC) contribute to the total organic aerosol mass and significantly alter absorption properties of the atmosphere. To date, their formation mechanisms are still ...not understood. In this work, the intriguing role of HNO2 (catalytic and oxidative) in the dark transformation of 3-methylcatechol (3MC) under atmospherically relevant aqueous-phase conditions is emphasized. Three possible pathways of dark 3-methyl-5-nitrocatechol and 3-methyl-4-nitrocatechol formation, markedly dependent on reaction conditions, were considered. In the dominant pathway, HNO2 is directly involved in the transformation of 3MC via consecutive oxidation and conjugated addition reactions (nonradical reaction mechanism). The two-step nitration dominates at a pH around the pK a of HNO2, which is typical for atmospheric aerosols, and is moderately dependent on temperature. Under very acidic conditions, the other two nitration pathways, oxidative aromatic nitration (electrophilic) and recombination of radical species, gain in importance. The predicted atmospheric lifetime of 3MC according to the dominant mechanism at these conditions (2.4 days at pH 4.5 and 25 °C) is more than 3-times shorter than that via the other two competitive pathways. Our results highlight the significance of a catechol oxidation-conjugated addition reaction in a nighttime secondary nitroaromatic chromophore formation in the atmosphere, especially in polluted environments with high NO x concentrations and relatively acidic particles (pH around 3).
Phenols are hazardous, but yet ubiquitous in the environment, including in atmospheric aerosols due to combustion emissions. There, phenols are subjected to secondary transformations, producing even ...more toxic nitrophenolic air pollutants. However, primary simple phenols, i.e. those containing only hydroxyl, methyl and methoxy substituents are not easy to detect. Trace concentrations, semi-volatile character and poorly ionizable functional groups prevent us from their determination by the most common analytical techniques, such as gas and liquid chromatography with mass spectrometric detection (GC/LC-MS). Here, we present a new derivatization method for MS/MS detection with positive ion electrospray ionization (+ESI-MS/MS) of simple phenols in atmospheric particulate matter (PM) extracts. The method is sensitive, selective, and robust, and requires no sample concentration step, which is critical due to the volatile character of the target analytes. After derivatization with dansyl chloride, phenol, catechol, cresols and guaiacol were detected in urban PM samples from Ljubljana, Slovenia. This method finally enables to study the abundance of primary phenols in atmospheric PM from different sources, which will improve understanding of secondary aerosol (trans)formation pathways and allow for more targeted mitigation strategies in respect to airborne phenolic pollutants.
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•Phenol dansylation improves ionization and enables LC-MS analysis.•Optimal reaction and measuring parameters provide very low limits of detection.•Phenol, catechol, guaiacol and cresol are determined in ambient particulate matter.•Concentrations of simple phenols in particulate matter are low, peaking in winter.•Simple phenols can be precursors to toxic secondary aerosols (e.g. nitrophenols).
A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-(3-cholamidopropyl)-dimethylammonium-1-propanesulfonate (CHAPS) has been carried out by isothermal ...titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ΔH M 0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ΔG M 0, and entropy, ΔS M 0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (n agg ≈ 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, Δc p,M 0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants.
Fine particulate matter (PM
2.5
) concentrations at the Middle Adriatic coastal site of Croatia were affected by different air-mass inflows and/or local sources and meteorological conditions, and ...peaked in summer. More polluted continental air-mass inflows mostly affected the area in the winter period, while southern marine pathways had higher impact in spring and summer. Chemical characterization of the water-soluble inorganic and organic ionic constituents is discussed with respect to seasonal trends, possible sources, and air-mass inputs. The largest contributors to the PM
2.5
mass were sea salts modified by the presence of secondary sulfate-rich aerosols indicated also by principal component analysis. SO
4
2−
was the prevailing anion, while the anthropogenic SO
4
2−
(anth-nssSO
4
2−
) dominantly constituted the major non-sea-salt SO
4
2−
(nssSO
4
2−
) fraction. Being influenced by the marine origin, its biogenic fraction (bio-nssSO
4
2−
) increased particularly in the spring. During the investigated period, aerosols were generally acidic. High Cl
−
deficit was observed at Middle Adriatic location for which the acid displacement is primarily responsible. With nssSO
4
2−
being dominant in Cl
−
depletion, sulfur-containing species from anthropogenic pollution emissions may have profound impact on atmospheric composition through altering chlorine chemistry in this region. However, when accounting for the neutralization of H
2
SO
4
by NH
3
, the potential of HNO
3
and organic acids to considerably influence Cl
−
depletion is shown to increase. Intensive open-fire events substantially increased the PM
2.5
concentrations and changed the water-soluble ion composition and aerosol acidity in summer of 2015. To our knowledge, this work presents the first time-resolved data evaluating the seasonal composition of water-soluble ions and their possible sources in PM
2.5
at the Middle Adriatic area. This study contributes towards a better understanding of atmospheric composition in the coastal Adriatic area and serves as a basis for the comparison with future studies related to the air quality at the coastal Adriatic and/or Mediterranean regions.
