Methanesulfonic acid (MSA) and SO formation from the addition channel of atmospheric dimethyl sulfide oxidation.

The formation of methanesulfonic acid (MSA) from the dimethyl sulfide addition channel primarily proceeds the reaction of methylsulfonyloxy radicals (CHSO) with H-atom donors, other than HO radicals. In competition with it, thermal decomposition of CHSO results in SO generation. The MSA/SO ratio is driven by the temperature dependence of CHSO decomposition.

Gas-Phase Formation of Sulfurous Acid (HSO) in the Atmosphere.

Sulfurous acid (HSO) is known to be thermodynamically instable decomposing into SO and HO. All attempts to detect this elusive acid in solution failed up to now. Reported HSO formation from an experiment carried out in a mass spectrometer as well as results from theoretical calculations, however, indicated a possible kinetic stability in the gas phase.

Highly Efficient Autoxidation of Triethylamine.

Autoxidation has been acknowledged as a major oxidation pathway in a broad range of atmospherically important compounds including isoprene and monoterpenes. More recently, autoxidation has also been identified as central and even dominant in the atmospheric oxidation of the rather small nonhydrocarbons dimethyl sulfide (DMS) and trimethylamine (TMA). Here, we find even faster autoxidation in the aliphatic amine triethylamine (TEA).

Direct sulfuric acid formation from the gas-phase oxidation of reduced-sulfur compounds.

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.

Large Gas-Phase Source of Esters and Other Accretion Products in the Atmosphere.

Dimeric accretion products have been observed both in atmospheric aerosol particles and in the gas phase. With their low volatilities, they are key contributors to the formation of new aerosol particles, acting as seeds for more volatile organic vapors to partition onto. Many particle-phase accretion products have been identified as esters.

Peroxy Radical and Product Formation in the Gas-Phase Ozonolysis of α-Pinene under Near-Atmospheric Conditions: Occurrence of an Additional Series of Peroxy Radicals O,O-CHO(O)O with = 1-3.

Ozonolysis of α-pinene, CH, and other monoterpenes is considered to be one of the important chemical process in the atmosphere leading to condensable vapors, which are relevant to aerosol formation and, finally, for Earth's radiation budget. The formation of peroxy (RO) radicals, O,O-CH(O)O with = 0-3, and closed-shell products has been probed from the ozonolysis of α-pinene for close to atmospheric reaction conditions. (The "O,O" in the chemical formulas indicates the two carbonyl groups formed in the ozonolysis.

Hydrotrioxide (ROOOH) formation in the atmosphere.

Organic hydrotrioxides (ROOOH) are known to be strong oxidants used in organic synthesis. Previously, it has been speculated that they are formed in the atmosphere through the gas-phase reaction of organic peroxy radicals (RO) with hydroxyl radicals (OH). Here, we report direct observation of ROOOH formation from several atmospherically relevant RO radicals.

Peroxy Radical Processes and Product Formation in the OH Radical-Initiated Oxidation of α-Pinene for Near-Atmospheric Conditions.

α-Pinene, CH, represents one of the most important biogenic emissions into the atmosphere. The formation of RO radicals HO-CHO, = 2-6, and their closed-shell products from the OH + α-pinene reaction has been measured for close to atmospheric reaction conditions in the presence of NO with concentrations of (1.7-490) × 10 molecules cm.

Atmospheric Fate of the CHSOO Radical from the CHS + O Equilibrium.

The atmospheric oxidation mechanisms of reduced sulfur compounds are of great importance in the biogeochemical sulfur cycle. The CHS radical represents an important intermediate in these oxidation processes. Under atmospheric conditions, CHS will predominantly react with O to form the peroxy radical CHSOO.

Trimethylamine Outruns Terpenes and Aromatics in Atmospheric Autoxidation.

Autoxidation in the atmosphere has been realized in the last decade as an important process that forms highly oxidized products relevant for the formation of secondary organic aerosol and likely with detrimental human health effects. It is experimentally shown that the OH radical-initiated oxidation of trimethylamine, the most highly emitted amine in the atmosphere, proceeds via rapid autoxidation steps dominating its atmospheric oxidation process. All three methyl groups are functionalized within a timescale of 10 s following the reaction with OH radicals leading to highly oxidized products.

Efficient alkane oxidation under combustion engine and atmospheric conditions.

Oxidation chemistry controls both combustion processes and the atmospheric transformation of volatile emissions. In combustion engines, radical species undergo isomerization reactions that allow fast addition of O. This chain reaction, termed autoxidation, is enabled by high engine temperatures, but has recently been also identified as an important source for highly oxygenated species in the atmosphere, forming organic aerosol.

SO formation and peroxy radical isomerization in the atmospheric reaction of OH radicals with dimethyl disulfide.

The atmospheric reaction of OH radicals with dimethyl disulfide, CH3SSCH3, proceeds primarily via OH addition forming CH3S and CH3SOH as reactive intermediates, and to a lesser extent via H-abstraction resulting in the peroxy radical CH3SSCH2OO in the presence of O2. The latter undergoes a fast two-step isomerization process leading to HOOCH2SSCHO. CH3S and CH3SOH are both converted to SO2 and CH3O2 with near unity yields under atmospheric conditions.

Atmospheric Autoxidation of Amines.

Autoxidation has been acknowledged as a major oxidation pathway in a broad range of atmospherically important compounds including isoprene, monoterpenes, and very recently, dimethyl sulfide. Here, we present a high-level theoretical multiconformer transition-state theory study of the atmospheric autoxidation in amines exemplified by the atmospherically important trimethylamine (TMA) and dimethylamine and generalized by the study of the larger diethylamine. Overall, we find that the initial hydrogen shift reactions have rate coefficients greater than 0.

Accretion Product Formation from Ozonolysis and OH Radical Reaction of α-Pinene: Mechanistic Insight and the Influence of Isoprene and Ethylene.

α-Pinene (CH) represents one of the most important biogenic emissions in the atmosphere. Its oxidation products can significantly contribute to the secondary organic aerosol (SOA) formation. Here, we report on the formation mechanism of C and C accretion products from α-pinene oxidation, which are believed to be efficient SOA precursors.

Accretion Product Formation from Self- and Cross-Reactions of RO Radicals in the Atmosphere.

Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas-phase reactions of two RO radicals produce accretion products composed of the carbon backbone of both reactants.

Direct Probing of Criegee Intermediates from Gas-Phase Ozonolysis Using Chemical Ionization Mass Spectrometry.

Criegee intermediates (CIs), mainly formed from gas-phase ozonolysis of alkenes, are considered as atmospheric oxidants besides OH and NO radicals as well as ozone. Direct CI measurement techniques are inevitably needed for reliable assessment of CIs' role in atmospheric processes. We found that CIs from ozonolysis reactions can be directly probed by means of chemical ionization mass spectrometry with a detection limit of about 10-10 molecules cm.

Formation of Highly Oxidized Radicals and Multifunctional Products from the Atmospheric Oxidation of Alkylbenzenes.

Aromatic hydrocarbons contribute significantly to tropospheric ozone and secondary organic aerosols (SOA). Despite large efforts in elucidating the formation mechanism of aromatic-derived SOA, current models still substantially underestimate the SOA yields when comparing to field measurements. Here we present a new, up to now undiscovered pathway for the formation of highly oxidized products from the OH-initiated oxidation of alkyl benzenes based on theoretical and experimental investigations.

endo-Cyclization of unsaturated RO radicals from the gas-phase ozonolysis of cyclohexadienes.

Unsaturated RO radicals from the ozonolysis of cyclodienes can readily undergo an endo-cyclization step under atmospheric conditions forming a new ring-containing RO radical after further O addition. This path represents an extension of the atmospheric autoxidation scheme forming highly oxidized multifunctional organic compounds (HOMs). HOMs play an important role for Earth's organic aerosol burden.

Highly Oxidized Second-Generation Products from the Gas-Phase Reaction of OH Radicals with Isoprene.

The gas-phase reaction of OH radicals with isoprene has been investigated in an atmospheric pressure flow tube at 293 ± 0.5 K with special attention to the second-generation products. Reaction conditions were optimized to achieve a predominant reaction of RO radicals with HO radicals.

Hydroxyl radical-induced formation of highly oxidized organic compounds.

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.

Molecular-scale evidence of aerosol particle formation via sequential addition of HIO.

Homogeneous nucleation and subsequent cluster growth leads to the formation of new aerosol particles in the atmosphere. The nucleation of sulfuric acid and organic vapours is thought to be responsible for the formation of new particles over continents, whereas iodine oxide vapours have been implicated in particle formation over coastal regions. The molecular clustering pathways that are involved in atmospheric particle formation have been elucidated in controlled laboratory studies of chemically simple systems, but direct molecular-level observations of nucleation in atmospheric field conditions that involve sulfuric acid, organic or iodine oxide vapours have yet to be reported.

Highly Oxidized RO2 Radicals and Consecutive Products from the Ozonolysis of Three Sesquiterpenes.

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.

Gas-Phase Ozonolysis of Cycloalkenes: Formation of Highly Oxidized RO2 Radicals and Their Reactions with NO, NO2, SO2, and Other RO2 Radicals.

The gas-phase reaction of ozone with C5-C8 cycloalkenes has been investigated in a free-jet flow system at atmospheric pressure and a temperature of 297 ± 1 K. Highly oxidized RO2 radicals bearing at least 5 O atoms in the molecule and their subsequent reaction products were detected in most cases by means of nitrate-CI-APi-TOF mass spectrometry. Starting from a Criegee intermediate after splitting-off an OH-radical, the formation of these RO2 radicals can be explained via an autoxidation mechanism, meaning RO2 isomerization (ROO → QOOH) and subsequently O2 addition (QOOH + O2 → R'OO).