Herrmann critically assesses recent developments in atmospheric aqueous phase chemistry with special emphasis on radical kinetics covering the period of 1996 to early 2003. Some recent new ...experimental approaches are summarized. Reviews on reactions of the most important radical oxidants are included.
The authors examined issues related to the tropospheric aqueous-phase chemistry. Topics discussed include nonphotolytic radical sources and nonradical oxidation reactions.
This critical review addresses the atmospheric gas phase and aqueous phase amine chemistry that is relevant to potential emissions from amine-based carbon capture and storage (CCS). The focus is on ...amine, nitrosamine and nitramine degradation, and nitrosamine and nitramine formation processes. A comparison between the relative importance of the various atmospheric sinks for amines, nitrosamines and nitramines is presented.
Oceans dominate emissions of dimethyl sulfide (DMS), the major natural sulfur source. DMS is important for the formation of non-sea salt sulfate (nss-SO₄2−) aerosols and secondary particulate matter ...over oceans and thus, significantly influence global climate. The mechanism of DMS oxidation has accordingly been investigated in several different model studies in the past. However, these studies had restricted oxidation mechanisms that mostly underrepresented important aqueous-phase chemical processes. These neglected but highly effective processes strongly impact direct product yields of DMS oxidation, thereby affecting the climatic influence of aerosols. To address these shortfalls, an extensive multiphase DMS chemistry mechanism, the Chemical Aqueous Phase Radical Mechanism DMS Module 1.0, was developed and used in detailed model investigations of multiphase DMS chemistry in the marine boundary layer. The performed model studies confirmed the importance of aqueous-phase chemistry for the fate of DMS and its oxidation products. Aqueous-phase processes significantly reduce the yield of sulfur dioxide and increase that of methyl sulfonic acid (MSA),which is needed to close the gap between modeled and measured MSA concentrations. Finally, the simulations imply that multiphase DMS oxidation produces equal amounts of MSA and sulfate, a result that has significant implications for nss-SO₄2− aerosol formation, cloud condensation nuclei concentration, and cloud albedo over oceans. Our findings show the deficiencies of parameterizations currently used in higher-scale models, which only treat gas-phase chemistry. Overall, this study shows that treatment of DMS chemistry in both gas and aqueous phases is essential to improve the accuracy of model predictions.
Detailed chemical analysis of wintertime PM10 collected at a rural village site in Germany showed the presence of a series of compounds that correlated very well with levoglucosan, a known biomass ...burning tracer compound. Nitrated aromatic compounds with molecular formula C7H7NO4 (M w 169) correlated particularly well with levoglucosan, indicating that they originated from biomass burning as well. These compounds were identified as a series of methyl-nitrocatechol isomers (4-methyl-5-nitrocatechol, 3-methyl-5-nitrocatechol, and 3-methyl-6-nitrocatechol) based on the comparison of their chromatographic and mass spectrometric behaviors to those from reference compounds. Aerosol chamber experiments suggest that m-cresol, which is emitted from biomass burning at significant levels, is a precursor for the detected methyl-nitrocatechols. The total concentrations of these compounds in the wintertime PM10 were as high as 29 ng m−3, indicating the secondary organic aerosol (SOA) originating from the oxidation of biomass burning VOCs contributed non-negligible amounts to the regional organic aerosol loading.
Organosulfates (OSs), also referred to as organic sulfate esters, are well-known and ubiquitous constituents of atmospheric aerosol particles. Commonly, they are assumed to form upon mixing of air ...masses of biogenic and anthropogenic origin, that is, through multiphase reactions between organic compounds and acidic sulfate particles. However, in contrast to this simplified picture, recent studies suggest that OSs may also originate from purely anthropogenic precursors or even directly from biomass and fossil fuel burning. Moreover, besides classical OS formation pathways, several alternative routes have been discovered, suggesting that OS formation possibly occurs through a wider variety of formation mechanisms in the atmosphere than initially expected. During the past decade, OSs have reached a constantly growing attention within the atmospheric science community with evermore studies reporting on large numbers of OS species in ambient aerosol. Nonetheless, estimates on OS concentrations and implications on atmospheric physicochemical processes are still connected to large uncertainties, calling for combined field, laboratory, and modeling studies. In this Critical Review, we summarize the current state of knowledge in atmospheric OS research, discuss unresolved questions, and outline future research needs, also in view of reductions of anthropogenic sulfur dioxide (SO2) emissions. Particularly, we focus on (1) field measurements of OSs and measurement techniques, (2) formation pathways of OSs and their atmospheric relevance, (3) transformation, reactivity, and fate of OSs in atmospheric particles, and (4) modeling efforts of OS formation and their global abundance.
Imidazoles formed via the reaction of dicarbonyls with nitrogen containing compounds in the atmospheric particle phase can be expected to initiate secondary organic aerosol (SOA) growth due to their ...potential to act as photosensitizers. Recent field studies quantified imidazoles for the first time in ambient aerosol samples from Europe and China. However, knowledge about the kinetics and mechanisms of particle-phase reactions involving imidazoles is still very limited. In the present study, the radical-driven aqueous-phase oxidative degradation reactions of the hydroxyl radical (·OH) with imidazoles were investigated. For the imidazoles, the following rate constants at 298 K and acidic conditions are obtained as k(imidazole-2-carboxaldehyde) = (1.8 ± 0.1) × 109 L mol–1 s–1, k(1-methylimidazole) = (2.3 ± 0.1) × 109 L mol–1 s–1, k(2-methylimidazole) = (3.9 ± 0.1) × 109 L mol–1 s–1, k(4-methylimidazole) = (3.2 ± 0.2) × 109 L mol–1 s–1, k(1-ethylimidazole) = (2.6 ± 0.1) × 109 L mol–1 s1, and k(2-ethylimidazole) = (3.9 ± 0.1) × 109 L mol–1 s–1. Temperature and pH dependencies of the reactions as well as the activation parameters have been determined and discussed. The possible implications and restrictions for imidazoles acting as photosensitizers in tropospheric particles have been considered.
Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation ...nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O ₃ and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.
Significance Extremely low volatility organic compounds (ELVOC) are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere. We show that the capability of biogenic VOC (BVOC) to produce ELVOC depends strongly on their chemical structure and relative oxidant levels. BVOC with an endocyclic double bond, representative emissions from, e.g., boreal forests, efficiently produce ELVOC from ozonolysis. Compounds with exocyclic double bonds or acyclic compounds including isoprene, emission representative of the tropics, produce minor quantities of ELVOC, and the role of OH radical oxidation is relatively larger. Implementing these findings into a global modeling framework shows that detailed assessment of ELVOC production pathways is crucial for understanding biogenic secondary organic aerosol and atmospheric CCN formation.
Explaining the formation of secondary organic aerosol is an intriguing question in atmospheric sciences because of its importance for Earth's radiation budget and the associated effects on health and ...ecosystems. A breakthrough was recently achieved in the understanding of secondary organic aerosol formation from ozone reactions of biogenic emissions by the rapid formation of highly oxidized multifunctional organic compounds via autoxidation. However, the important daytime hydroxyl radical reactions have been considered to be less important in this process. Here we report measurements on the reaction of hydroxyl radicals with α- and β-pinene applying improved mass spectrometric methods. Our laboratory results prove that the formation of highly oxidized products from hydroxyl radical reactions proceeds with considerably higher yields than previously reported. Field measurements support these findings. Our results allow for a better description of the diurnal behaviour of the highly oxidized product formation and subsequent secondary organic aerosol formation in the atmosphere.
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