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  • 1
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    Molecular understanding of new-particle formation from 〈i〉α〈/i〉-pinene between −50 and +25 °C
    Copernicus GmbH ; 2020
    In:  Atmospheric Chemistry and Physics Vol. 20, No. 15 ( 2020-08-03), p. 9183-9207
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 15 ( 2020-08-03), p. 9183-9207
    Abstract: Abstract. Highly oxygenated organic molecules (HOMs) contribute substantially to the formation and growth of atmospheric aerosol particles, which affect air quality, human health and Earth's climate. HOMs are formed by rapid, gas-phase autoxidation of volatile organic compounds (VOCs) such as α-pinene, the most abundant monoterpene in the atmosphere. Due to their abundance and low volatility, HOMs can play an important role in new-particle formation (NPF) and the early growth of atmospheric aerosols, even without any further assistance of other low-volatility compounds such as sulfuric acid. Both the autoxidation reaction forming HOMs and their NPF rates are expected to be strongly dependent on temperature. However, experimental data on both effects are limited. Dedicated experiments were performed at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN to address this question. In this study, we show that a decrease in temperature (from +25 to −50 ∘C) results in a reduced HOM yield and reduced oxidation state of the products, whereas the NPF rates (J1.7 nm) increase substantially. Measurements with two different chemical ionization mass spectrometers (using nitrate and protonated water as reagent ion, respectively) provide the molecular composition of the gaseous oxidation products, and a two-dimensional volatility basis set (2D VBS) model provides their volatility distribution. The HOM yield decreases with temperature from 6.2 % at 25 ∘C to 0.7 % at −50 ∘C. However, there is a strong reduction of the saturation vapor pressure of each oxidation state as the temperature is reduced. Overall, the reduction in volatility with temperature leads to an increase in the nucleation rates by up to 3 orders of magnitude at −50 ∘C compared with 25 ∘C. In addition, the enhancement of the nucleation rates by ions decreases with decreasing temperature, since the neutral molecular clusters have increased stability against evaporation. The resulting data quantify how the interplay between the temperature-dependent oxidation pathways and the associated vapor pressures affect biogenic NPF at the molecular level. Our measurements, therefore, improve our understanding of pure biogenic NPF for a wide range of tropospheric temperatures and precursor concentrations.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-20-9183-2020
    DOI: 10.5194/acp-20-9183-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
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  • 2
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    The role of ions in new particle formation in the CLOUD chamber
    Copernicus GmbH ; 2017
    In:  Atmospheric Chemistry and Physics Vol. 17, No. 24 ( 2017-12-21), p. 15181-15197
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 17, No. 24 ( 2017-12-21), p. 15181-15197
    Abstract: Abstract. The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nanoparticle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e., in conditions in which neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.5 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.5 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.5 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-17-15181-2017
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
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  • 3
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    Molecular understanding of the suppression of new-particle formation by isoprene
    Copernicus GmbH ; 2020
    In:  Atmospheric Chemistry and Physics Vol. 20, No. 20 ( 2020-10-20), p. 11809-11821
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 20, No. 20 ( 2020-10-20), p. 11809-11821
    Abstract: Abstract. Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms – which drive particle nucleation and early growth – while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C20 and C15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2⚫) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene ∕ monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH⚫) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2⚫ radicals that reduce C20 formation. RO2⚫ termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-20-11809-2020
    DOI: 10.5194/acp-20-11809-2020-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
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  • 4
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    Influence of temperature on the molecular composition of ions and charged clusters during pure biogenic nucleation
    Copernicus GmbH ; 2018
    In:  Atmospheric Chemistry and Physics Vol. 18, No. 1 ( 2018-01-04), p. 65-79
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 1 ( 2018-01-04), p. 65-79
    Abstract: Abstract. It was recently shown by the CERN CLOUD experiment that biogenic highly oxygenated molecules (HOMs) form particles under atmospheric conditions in the absence of sulfuric acid, where ions enhance the nucleation rate by 1–2 orders of magnitude. The biogenic HOMs were produced from ozonolysis of α-pinene at 5 ∘C. Here we extend this study to compare the molecular composition of positive and negative HOM clusters measured with atmospheric pressure interface time-of-flight mass spectrometers (APi-TOFs), at three different temperatures (25, 5 and −25 ∘C). Most negative HOM clusters include a nitrate (NO3-) ion, and the spectra are similar to those seen in the nighttime boreal forest. On the other hand, most positive HOM clusters include an ammonium (NH4+) ion, and the spectra are characterized by mass bands that differ in their molecular weight by ∼ 20 C atoms, corresponding to HOM dimers. At lower temperatures the average oxygen to carbon (O : C) ratio of the HOM clusters decreases for both polarities, reflecting an overall reduction of HOM formation with decreasing temperature. This indicates a decrease in the rate of autoxidation with temperature due to a rather high activation energy as has previously been determined by quantum chemical calculations. Furthermore, at the lowest temperature (−25 ∘C), the presence of C30 clusters shows that HOM monomers start to contribute to the nucleation of positive clusters. These experimental findings are supported by quantum chemical calculations of the binding energies of representative neutral and charged clusters.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-18-65-2018
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
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  • 5
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    The driving factors of new particle formation and growth in the polluted boundary layer
    Copernicus GmbH ; 2021
    In:  Atmospheric Chemistry and Physics Vol. 21, No. 18 ( 2021-09-27), p. 14275-14291
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 18 ( 2021-09-27), p. 14275-14291
    Abstract: Abstract. New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols is important to develop effective mitigation strategies. However, NPF rates reported in the polluted boundary layer span more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been postulated to participate in NPF, including sulfuric acid, ammonia, amines and organics, but their relative roles remain unclear. We investigated NPF in the CLOUD chamber using mixtures of anthropogenic vapours that simulate polluted boundary layer conditions. We demonstrate that NPF in polluted environments is largely driven by the formation of sulfuric acid–base clusters, stabilized by the presence of amines, high ammonia concentrations and lower temperatures. Aromatic oxidation products, despite their extremely low volatility, play a minor role in NPF in the chosen urban environment but can be important for particle growth and hence for the survival of newly formed particles. Our measurements quantitatively account for NPF in highly diverse urban environments and explain its large observed variability. Such quantitative information obtained under controlled laboratory conditions will help the interpretation of future ambient observations of NPF rates in polluted atmospheres.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-21-14275-2021
    DOI: 10.5194/acp-21-14275-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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  • 6
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    Characterization of the mass-dependent transmission efficiency of a CIMS
    Copernicus GmbH ; 2016
    In:  Atmospheric Measurement Techniques Vol. 9, No. 4 ( 2016-04-04), p. 1449-1460
    Details
    In: Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 9, No. 4 ( 2016-04-04), p. 1449-1460
    Abstract: Abstract. Knowledge about mass discrimination effects in a chemical ionization mass spectrometer (CIMS) is crucial for quantifying, e.g., the recently discovered extremely low volatile organic compounds (ELVOCs) and other compounds for which no calibration standard exists so far. Here, we present a simple way of estimating mass discrimination effects of a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. Characterization of the mass discrimination is achieved by adding different perfluorinated acids to the mass spectrometer in amounts sufficient to deplete the primary ions significantly. The relative transmission efficiency can then be determined by comparing the decrease of signals from the primary ions and the increase of signals from the perfluorinated acids at higher masses. This method is in use already for PTR-MS; however, its application to a CI-APi-TOF brings additional difficulties, namely clustering and fragmentation of the measured compounds, which can be treated with statistical analysis of the measured data, leading to self-consistent results. We also compare this method to a transmission estimation obtained with a setup using an electrospray ion source, a high-resolution differential mobility analyzer and an electrometer, which estimates the transmission of the instrument without the CI source. Both methods give different transmission curves, indicating non-negligible mass discrimination effects of the CI source. The absolute transmission of the instrument without the CI source was estimated with the HR-DMA method to plateau between the m∕z range of 127 and 568 Th at around 1.5 %; however, for the CI source included, the depletion method showed a steady increase in relative transmission efficiency from the m∕z range of the primary ion (mainly at 62 Th) to around 550 Th by a factor of around 5. The main advantages of the depletion method are that the instrument is used in the same operation mode as during standard measurements and no knowledge of the absolute amount of the measured substance is necessary, which results in a simple setup.
    Type of Medium: Online Resource
    ISSN: 1867-8548
    URL: Article
    DOI: 10.5194/amt-9-1449-2016
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
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  • 7
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    An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles
    Copernicus GmbH ; 2023
    In:  Atmospheric Chemistry and Physics Vol. 23, No. 11 ( 2023-06-15), p. 6613-6631
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 23, No. 11 ( 2023-06-15), p. 6613-6631
    Abstract: Abstract. Currently, the complete chemical characterization of nanoparticles (〈 100 nm) represents an analytical challenge, since these particles are abundant in number but have negligible mass. Several methods for particle-phase characterization have been recently developed to better detect and infer more accurately the sources and fates of sub-100 nm particles, but a detailed comparison of different approaches is missing. Here we report on the chemical composition of secondary organic aerosol (SOA) nanoparticles from experimental studies of α-pinene ozonolysis at −50, −30, and −10 ∘C and intercompare the results measured by different techniques. The experiments were performed at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). The chemical composition was measured simultaneously by four different techniques: (1) thermal desorption–differential mobility analyzer (TD–DMA) coupled to a NO3- chemical ionization–atmospheric-pressure-interface–time-of-flight (CI–APi–TOF) mass spectrometer, (2) filter inlet for gases and aerosols (FIGAERO) coupled to an I− high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS), (3) extractive electrospray Na+ ionization time-of-flight mass spectrometer (EESI-TOF), and (4) offline analysis of filters (FILTER) using ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS). Intercomparison was performed by contrasting the observed chemical composition as a function of oxidation state and carbon number, by estimating the volatility and comparing the fraction of volatility classes, and by comparing the thermal desorption behavior (for the thermal desorption techniques: TD–DMA and FIGAERO) and performing positive matrix factorization (PMF) analysis for the thermograms. We found that the methods generally agree on the most important compounds that are found in the nanoparticles. However, they do see different parts of the organic spectrum. We suggest potential explanations for these differences: thermal decomposition, aging, sampling artifacts, etc. We applied PMF analysis and found insights of thermal decomposition in the TD–DMA and the FIGAERO.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-23-6613-2023
    DOI: 10.5194/acp-23-6613-2023-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2023
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  • 8
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    Evaluation of the coupled high-resolution atmospheric chemistry model system MECO(n) using in situ and MAX-DOAS NO〈sub〉2〈/sub〉 measurements
    Copernicus GmbH ; 2021
    In:  Atmospheric Measurement Techniques Vol. 14, No. 7 ( 2021-07-30), p. 5241-5269
    Details
    In: Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 14, No. 7 ( 2021-07-30), p. 5241-5269
    Abstract: Abstract. We present high spatial resolution (up to 2.2×2.2 km2) simulations focussed over south-west Germany using the online coupled regional atmospheric chemistry model system MECO(n) (MESSy-fied ECHAM and COSMO models nested n times). Numerical simulation of nitrogen dioxide (NO2) surface volume mixing ratios (VMRs) are compared to in situ measurements from a network with 193 locations including background, traffic-adjacent and industrial stations to investigate the model's performance in simulating the spatial and temporal variability of short-lived chemical species. We show that the use of a high-resolution and up-to-date emission inventory is crucial for reproducing the spatial variability and resulted in good agreement with the measured VMRs at the background and industrial locations with an overall bias of less than 10 %. We introduce a computationally efficient approach that simulates diurnal and daily variability in monthly-resolved anthropogenic emissions to resolve the temporal variability of NO2. MAX-DOAS (Multiple AXis Differential Optical Absorption Spectroscopy) measurements performed at Mainz (49.99∘ N, 8.23∘ E) were used to evaluate the simulated tropospheric vertical column densities (VCDs) of NO2. We propose a consistent and robust approach to evaluate the vertical distribution of NO2 in the boundary layer by comparing the individual differential slant column densities (dSCDs) at various elevation angles. This approach considers details of the spatial heterogeneity and sensitivity volume of the MAX-DOAS measurements while comparing the measured and simulated dSCDs. The effects of clouds on the agreement between MAX-DOAS measurements and simulations have also been investigated. For low elevation angles (≤8∘), small biases in the range of −14 % to +7 % and Pearson correlation coefficients in the range of 0.5 to 0.8 were achieved for different azimuth directions in the cloud-free cases, indicating good model performance in the layers close to the surface. Accounting for diurnal and daily variability in the monthly-resolved anthropogenic emissions was found to be crucial for the accurate representation of time series of measured NO2 VMR and dSCDs and is particularly critical when vertical mixing is suppressed, and the atmospheric lifetime of NO2 is relatively long.
    Type of Medium: Online Resource
    ISSN: 1867-8548
    URL: Article
    DOI: 10.5194/amt-14-5241-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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  • 9
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    Cycling and retention of nitrogen in European beech (〈i〉Fagus sylvatica〈/i〉 L.) ecosystems under elevated fructification frequency
    Copernicus GmbH ; 2021
    In:  Biogeosciences Vol. 18, No. 12 ( 2021-06-23), p. 3763-3779
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 18, No. 12 ( 2021-06-23), p. 3763-3779
    Abstract: Abstract. Atmospheric deposition of nitrogen (N) has exceeded its demand for plant increment in forest ecosystems in Germany. High N inputs increased plant growth, the internal N cycling within the ecosystem, the retention of N in soil and plant compartments, and the N output by seepage water. But the processes involved are not fully understood, notably the effect of fructification in European beech (Fagus sylvatica L.) on N fluxes. The frequency of fructification has increased together with air temperature and N deposition, but its impact on N fluxes and the sequestration of carbon (C) and N in soils have been hardly studied. A field experiment using 15N-labeled leaf litter exchange was carried out over a 5.5-year period at seven long-term European beech (Fagus sylvatica L.) monitoring sites to study the impact of current mast frequency on N cycling. Mean annual leaf litterfall contained 35 kg N ha−1, but about one-half of that was recovered in the soil 5.5 years after the establishment of the leaf litter 15N exchange experiment. In these forests, fructification occurred commonly at intervals of 5 to 10 years, which has now changed to every 2 years as observed during this study period. Seed cupules contributed 51 % to the additional litterfall in mast years, which creates a high nutrient demand during their decomposition due to the very high ratios of C to N and C to phosphorus (P). Retention of leaf litter 15N in the soil was more closely related to the production of total litterfall than to the leaf litterfall, indicating the role of seed cupules in the amount of leaf N retained in the soil. Higher mast frequency increased the mass of mean annual litterfall by about 0.5 Mg ha−1 and of litterfall N by 8.7 kg ha−1. Mean net primary production (NPP) increased by about 4 %. Mean total N retention in soils calculated by input and output fluxes was unrelated to total litterfall, indicating that mast events were not the primary factor controlling total N retention in soils. Despite reduced N deposition since the 1990s, about 5.7 out of 20.7 kg N ha−1 deposited annually between 1994 and 2008 was retained in soils, notably at acid sites with high N/P and C/P ratios in the organic layers and mineral soils, indicating P limitation for litter decomposition. Trees retained twice as much N compared to soils by biomass increment, particularly in less acidic stands where the mineral soils had low C/N ratios. These results have major implications for our understanding of the C and N cycling and N retention in forest ecosystems. In particular the role of mast products in N retention needs more research in the future.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-18-3763-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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  • 10
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    Chemical composition of nanoparticles from 〈i〉α〈/i〉-pinene nucleation and the influence of isoprene and relative humidity at low temperature
    Copernicus GmbH ; 2021
    In:  Atmospheric Chemistry and Physics Vol. 21, No. 22 ( 2021-11-25), p. 17099-17114
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 21, No. 22 ( 2021-11-25), p. 17099-17114
    Abstract: Abstract. Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    URL: Article
    DOI: 10.5194/acp-21-17099-2021
    DOI: 10.5194/acp-21-17099-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
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