•A number of quantum yields for the photolysis of iron-carboxylato complexes have been determined.•Reaction mechanisms are discussed.•The quantum yields are of interest in environmental chemistry.
...Fe(III) carboxylato complex photochemistry can be of interest for environmental aqueous systems, oxidative processing of wastewater or laboratory photochemical applications in general. A comprehensive dataset of Fe2+ quantum yields from the photolysis of aqueous Fe(III) complexes with malonate, succinate, glutarate, dl-tartrate, tartronate, gluconate, dl-lactate, dl-malate, pyruvate and glyoxalate has been measured. Irradiation techniques included single laser flash photolysis at 308 and 351nm and continuous photolysis with a Hg(Xe) lamp-monochromator system at 313, 366, 405 and 436nm. Complexes with ligands having a higher oxygen to carbon ratio tend to exhibit better photoreduction ability. Ligands containing OH, keto or diol functional groups in the α-position exhibit higher quantum yields than unsubstituted carboxylates (R-CH2-COOH). Generally, dissolved O2 lowers the Fe2+ quantum yield but at certain wavelengths, for some ligands this is the opposite. The influence of transient decay pathways and secondary red-ox reactions including interactions with dissolved O2 has been investigated for Fe(III) glyoxalato complexes using kinetic simulations. Some complexes show a dependence of Fe2+ quantum yield on the irradiation energy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The formation of highly oxidized multifunctional organic compounds (HOMs) from the ozonolysis of three sesquiterpenes, α-cedrene, β-caryophyllene, and α-humulene, was investigated for the first time. ...Sesquiterpenes contribute 2.4% to the global carbon emission of biogenic volatile organic compounds (BVOCs) and can be responsible for up to 70% of the regional BVOC emissions. HOMs were detected with chemical ionization−atmospheric pressure interface−time-of-flight mass spectrometry and nitrate and acetate ionization. Acetate ions were more sensitive toward highly oxidized RO2 radicals containing a single hydroperoxide moiety. Under the chosen reaction conditions, product formation was dominated by highly oxidized RO2 radicals which react with NO, NO2, HO2, and other RO2 radicals under atmospheric conditions. The ozonolysis of sesquiterpenes resulted in molar HOM yields of 0.6% for α-cedrene (acetate), 1.8% for β-caryophyllene (acetate), and 1.4% for α-humulene (nitrate) afflicted with an uncertainty factor of 2. Molar yields of highly oxidized RO2 radicals were identical with HOM yields measuring the corresponding closed-shell products. HOM formation from ozonolysis of α-cedrene was explained by an autoxidation mechanism initiated by ozone attack at the double bond similar to that found in the ozonolysis of cyclohexene and limonene.
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IJS, KILJ, NUK, PNG, UL, UM
Sulfuric acid represents a fundamental precursor for new nanometre-sized atmospheric aerosol particles. These particles, after subsequent growth, may influence Earth´s radiative forcing directly, or ...indirectly through affecting the microphysical and radiative properties of clouds. Currently considered formation routes yielding sulfuric acid in the atmosphere are the gas-phase oxidation of SO
initiated by OH radicals and by Criegee intermediates, the latter being of little relevance. Here we report the observation of immediate sulfuric acid production from the OH reaction of emitted organic reduced-sulfur compounds, which was speculated about in the literature for decades. Key intermediates are the methylsulfonyl radical, CH
SO
, and, even more interestingly, its corresponding peroxy compound, CH
SO
OO. Results of modelling for pristine marine conditions show that oxidation of reduced-sulfur compounds could be responsible for up to ∼50% of formed gas-phase sulfuric acid in these areas. Our findings provide a more complete understanding of the atmospheric reduced-sulfur oxidation.
Terpene-derived acids formed through the atmospheric gas-phase oxidation of terpenes are able to efficiently undergo a phase transfer into the aqueous phase. The subsequent aqueous-phase oxidation of ...such compounds has not been intensely studied. Accordingly, the aqueous-phase second-order rate constants of the oxidation reactions of cis-pinonic acid (CPA) and (+)-camphoric acid (+CA) with hydroxyl radicals (•OH), nitrate radicals (NO3 •), and sulfate radicals (SO4 •–) were investigated as a function of temperature and pH in the present study. For CPA and +CA the following •OH reaction rate constants at T = 298 K are determined: k second(CPA, pH<2) = (2.8 ± 0.1) × 109 L mol–1 s–1, k second(CPA, pH>8) = (2.7 ± 0.3) × 109 L mol–1 s–1, k second(+CA, pH<2) = (2.1 ± 0.1) × 109 L mol–1 s–1, k second(+CA, pH=5.3) = (2.7 ± 0.3) × 109 L mol–1 s–1, k second(+CA, pH>8) = (2.7 ± 0.1) × 109 L mol–1 s–1. In order to assess the atmospheric impact of the aqueous-phase oxidation of such compounds, atmospheric aqueous-phase lifetimes were calculated for two model scenarios based on CAPRAM 3.0i. The aqueous-phase oxidation under remote conditions emerges to be the most favored pathway with lifetimes of 5 ± 1 h.
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► Aqueous solutions of Fe(III)-oxalato complexes were photolyzed. ► The Fe(II) quantum yield decreases at Fe(III)<1×10−3M. ► Excitation energy influences Fe(II) quantum yield of ...dilute ferrioxalate solutions. ► 1:2 Fe(III)-oxalato complexes show higher quantum yields than 1:3 complexes.
Iron(III)oxalato complexes do frequently occur in the environment, specifically in surface waters, in atmospheric waters (clouds, rain, fog) or in waste waters. Due to their high photo-reactivity and their absorption overlap with the actinic spectrum, Fe(III)oxalato complex photochemistry is widespread and of broad interest. Fe(III)oxalato complex photolysis in deaerated solutions using single excimer laser flash photolysis at 308 and 351nm and continuous Hg(Xe)-lamp irradiation at 313, 366 and 436nm was quantified via Fe(II) quantum yield measurements with phenanthroline complexometry and UV–vis detection. Measured Fe(II) quantum yields showed a dependence on initial Fe(III)ferrioxalate concentration and irradiation energy at below millimolar concentrations. Individual molar extinctions (in lmol−1cm−1) and individual quantum yields (Φ) were determined for initial Fe(III) concentrations of 4.85×10−4M for the 1:2 (FeOx2−) and 1:3 (FeOx33−) complexes applying a regression analysis for solutions containing variable ratios of 1:2 and 1:3 complexes: ɛ1:2, 308nm=2300±90, ɛ1:3, 308nm=2890±40, Φ1:3, 308nm=0.93±0.09; ɛ1:2, 351nm=1040±30, ɛ1:3, 351nm=1120±20, Φ1:3, 351nm=0.88±0.08; ɛ1:2, 313nm=2055±111, ɛ1:3, 313nm=2663±37, Φ1:3, 313nm=0.12±0.05; ɛ1:2, 366nm=753±357, ɛ1:3, 366nm=709±10, Φ1:2, 366nm=1.17±1.46, Φ1:3, 366nm=0.91±0.09; ɛ1:2, 436nm=55±9, ɛ1:3, 436nm=22±2, Φ1:2, 436nm=1.40±0.40, Φ1:3, 436nm=1.00±0.20. Individual quantum yields for the 1:2 complex could only be determined for the excitation wavelengths 366 and 436nm due to non-linearity of the data for 308, 351 and 313nm. The non-linearity is ascribed to complicated interactions of secondary reactions involving Fe(III)oxalato educt-complexes, carboxyl radicals and Fe(II)-radical complexes. The 1:2 complex has generally a higher quantum yield compared to the 1:3 complex at all considered wavelengths.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Investigation of the consecutive reactions of first-generation terpene oxidation products provides insight into the formation of secondary organic aerosol (SOA). To this end, OH radical reactions ...with α-pinene, β-pinene, and limonene were examined along with the OH-oxidation of nopinone as a β-pinene oxidation product and pinonaldehyde and myrtenal as α-pinene oxidation products. The SOA yield of β-pinene (0.50) was much higher than that of α-pinene (0.35) and the limonene/OH system (0.30). This is opposite to the ozonolysis SOA yields described in the literature. The growth curve of SOA from β-pinene shows the contribution of secondary reactions, such as further reaction of nopinone. This contribution (17%) and the high SOA yield of nopinone (0.24) might lead to the high SOA formation potential observed for β-pinene. The majority of the C9 oxidation products observed from β-pinene can be attributed to the consecutive reaction of nopinone, whereas in the case of pinonaldehyde, only a few α-pinene oxidation products were identified. Nopinone contributes significantly to the formation of pinic acid (51%), homoterpenylic acid (74%), and 3-methyl-1,2,3-butane-tricarboxylic acid (MBTCA, 88%) during β-pinene oxidation. The oxidation of pinonaldehyde was expected to produce important SOA markers, but only negligible amounts were identified. This indicates that their formation by oxidation of α-pinene must proceed via different pathways from the further oxidation of pinonaldehyde. Only pinonic acid and MBTCA were found in considerable amounts and were formed in α-pinene oxidation with 57% yield, while that for the pinonaldehyde/OH reaction was 33%. The lack of important SOA marker compounds might cause the low SOA yield (0.07) observed for pinonaldehyde. Based on the low SOA yield, pinonaldehyde contributes only 4.5% to α-pinene SOA. Myrtenal was identified among the gas-phase products of α-pinene oxidation. A majority of α-pinene SOA marker compounds was indeed formed by myrtenal oxidation, especially terebic acid (84%), pinic acid (76%), and diaterpenylic acid acetate (DTAA; 40%). In general, the contribution of myrtenal to α-pinene SOA is estimated to be as high as 23%. Among the detected compounds, homoterpenylic acid was positively identified as a new SOA marker compound, which was formed from β-pinene/OH and nopinone/OH but not from α-pinene/OH. A new reaction pathway yielding MBTCA was also identified in the β-pinene/OH system formed by the oxidation of nopinone, while in the case of α-pinene, the oxidation of pinonaldehyde yielded MBTCA.
•SOA formation potential of β-pinene/OH > α-pinene/OH > limonene/OH.•Oxidation of first-generation oxidation products enables insights into the formation of secondary organic aerosol (SOA).•New reaction channels yielding SOA marker compounds.•First analytical evidence for homoterpenylic acid – a SOA marker compound.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity ...of atmospheric aqueous phases, e.g., deliquesced aerosol particles, cloud, and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, which involve both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight the need for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and the need for advancements in field and laboratory measurements and model tools.
Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of ...aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO2 radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O2 addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.
Not only in the solution phase: Highly oxidized RO2 radicals in the atmosphere are rapidly formed by autoxidation initiated by the reaction of O3 and OH radicals with biogenic emissions such as limonene and α‐pinene. Field measurements (see picture) confirm experimental findings from a flow‐tube study. The closed‐shell products from this process represent important aerosol constituents influencing aerosol–cloud–climate interactions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Imidazoles are widely discussed in recent literature. They have been studied as a secondary product of the reaction of dicarbonyls with nitrogen containing compounds in a number of laboratory ...studies, potentially acting as photosensitizers triggering secondary organic aerosol growth and are forming constituents of light absorbing brown carbon. Despite the knowledge from laboratory studies, no quantitative information about imidazoles in ambient aerosol particles is available. Within the present study, five imidazoles (1-butylimidazole, 1-ethylimidazole, 2-ethylimidazole, imidazol-2-carboxaldehyde, and 4(5)-methylimidazole) were successfully identified and quantified for the first time in ambient aerosol samples from different environments in Europe and China. Their concentrations range between 0.2 and 14 ng/m3. 4(5)-Methylimidazole was found to be the most abundant imidazole. The occurrence of imidazoles seems to be favored at sites with strong biomass burning influence or connected to more polluted air masses. No connection was found between aerosol particle pH and imidazole concentration. Our work corroborates the laboratory studies by showing that imidazoles are present in ambient aerosol samples in measurable amounts. Moreover, it further motivates to explore the potential photosensitizing properties of small alkyl-substituted imidazoles.
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Recent studies pointed to a high ice nucleating activity (INA) in the Arctic sea surface microlayer (SML). However, related chemical information is still sparse. In the present study, INA and free ...glucose concentrations were quantified in Arctic SML and bulk water samples from the marginal ice zone, the ice-free ocean, melt ponds, and open waters within the ice pack. T 50 (defining INA) ranged from −17.4 to −26.8 °C. Glucose concentrations varied from 0.6 to 51 μg/L with highest values in the SML from the marginal ice zone and melt ponds (median 16.3 and 13.5 μg/L) and lower values in the SML from the ice pack and the ice-free ocean (median 3.9 and 4.0 μg/L). Enrichment factors between the SML and the bulk ranged from 0.4 to 17. A positive correlation was observed between free glucose concentration and INA in Arctic water samples (T 50(°C) = (−25.6 ± 0.6) + (0.15 ± 0.04)·Glucose(μg/L), R P = 0.66, n = 74). Clustering water samples based on phytoplankton pigment composition resulted in robust but different correlations within the four clusters (R P between 0.67 and 0.96), indicating a strong link to phytoplankton-related processes. Since glucose did not show significant INA itself, free glucose may serve as a potential tracer for INA in Arctic water samples.
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