Showing papers by "Thomas F. Mentel published in 2019"
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TL;DR: This Review defines HOM and describes the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties.
Abstract: Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earth's radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.
409 citations
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University of Manchester1, Forschungszentrum Jülich2, University of Eastern Finland3, Stockholm University4, Fudan University5, University of Gothenburg6, Norwegian Meteorological Institute7, Chalmers University of Technology8, Swedish Meteorological and Hydrological Institute9, University of Helsinki10, University of Washington11, California Institute of Technology12, University of Cologne13
TL;DR: It is shown that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours, suggesting that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically.
Abstract: Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene ‘scavenges’ hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production). Adding reactive gases such as isoprene to mixtures lowers the production of secondary organic aerosol in the atmosphere, thus reducing the atmospheric particulate burden, with implications for human health and climate.
189 citations
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TL;DR: In this paper, the results from a flow reactor study on theformation of carboxylic acids from limonene oxidation in the presence of fixmeone under NOx -free conditions in the dark were presented.
Abstract: . This work presents the results from a flow reactor study on the
formation of carboxylic acids from limonene oxidation in the presence of
ozone under NOx -free conditions in the dark. A High-Resolution Time-of-Flight acetate Chemical Ionisation Mass Spectrometer (HR-ToF-CIMS) was used in combination with a Filter Inlet for Gases and AEROsols (FIGAERO)
to measure the carboxylic acids in the gas and particle phases. The results
revealed that limonene oxidation produced large amounts of carboxylic acids
which are important contributors to secondary organic aerosol (SOA)
formation. The highest 10 acids contributed 56 %–91 % to the total
gas-phase signal, and the dominant gas-phase species in most experiments were
C8H12O4 , C9H14O4 , C7H10O4 and
C10H16O3 . The particle-phase composition was generally more
complex than the gas-phase composition, and the highest 10 acids contributed
47 %–92 % to the total signal. The dominant species in the particle phase
were C8H12O5 , C9H14O5 , C9H12O5
and C10H16O4 . The measured concentration of dimers bearing at
least one carboxylic acid function in the particle phase was very low,
indicating that acidic dimers play a minor role in SOA formation via
ozone ( O3 )/hydroxyl (OH) oxidation of limonene. Based on the various experimental
conditions, the acidic compositions for all experiments were modelled using
descriptions from the Master Chemical Mechanism (MCM). The experiment
and model provided a yield of large ( C7 – C10 ) carboxylic acid of the order of 10 % (2 %–23 % and 10 %–15 %, respectively). Significant concentrations of 11
acids, from a total of 16 acids, included in the MCM were measured with the
CIMS. However, the model predictions were, in some cases, inconsistent with
the measurement results, especially regarding the OH dependence.
Reaction mechanisms are suggested to fill-in the knowledge gaps. Using the
additional mechanisms proposed in this work, nearly 75 % of the observed
gas-phase signal in our lowest concentration experiment (8.4 ppb converted, ca. 23 % acid yield) carried out under humid conditions can be understood.
30 citations
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TL;DR: In this paper, the measurement of HO2 using chemical ionisation combined with a high-resolution time-of-flight (TOSF) mass spectrometer employing bromide as the primary ion is presented.
Abstract: . Hydroxyl and hydroperoxy radicals are key species for the understanding of
atmospheric oxidation processes. Their measurement is challenging due to
their high reactivity; therefore, very sensitive detection methods are needed.
Within this study, the measurement of hydroperoxy radicals ( HO2 )
using chemical ionisation combined with a high-resolution time-of-flight
mass spectrometer (Aerodyne Research Inc.) employing bromide as the primary ion
is presented. The sensitivity reached is equal to 0.005×108 HO2 cm −3 for 10 6 cps of bromide and 60 s of integration time, which is
below typical HO2 concentrations found in the atmosphere. The
detection sensitivity of the instrument is affected by the presence of water
vapour. Therefore, a water-vapour-dependent calibration factor that decreases
approximately by a factor of 2 if the water vapour mixing ratio increases from
0.1 % to 1.0 % needs to be applied. An instrumental background, most
likely generated by the ion source that is equivalent to a HO2
concentration of ( 1.5 ± 0.2 ) × 10 8 molecules cm−3 , is
subtracted to derive atmospheric HO2 concentrations. This background
can be determined by overflowing the inlet with zero air. Several experiments
were performed in the atmospheric simulation chamber SAPHIR at the
Forschungszentrum Julich to test the instrument performance in comparison
to the well-established laser-induced fluorescence (LIF) technique for
measurements of HO2 . A highly linear correlation coefficient of
R2=0.87 is achieved. The slope of the linear regression of 1.07
demonstrates the good absolute agreement of both measurements. Chemical
conditions during experiments allowed for testing the instrument's behaviour in
the presence of atmospheric concentrations of H2O , NOx , and
O3 . No significant interferences from these species were observed.
All of these facts demonstrate a reliable measurement of HO2 by
the chemical ionisation mass spectrometer presented.
17 citations
27 Mar 2019
TL;DR: Highly oxygenated organic molecules (HOMs) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC) and can contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earth's radiation balance as discussed by the authors.
Abstract: Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earth’s radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research.
4 citations