Ionicon Analytik (Austria)

Abstract It has been well-known and studied that the quantification of various compounds with Proton-Transfer-Reaction—Mass Spectrometry (PTR-MS) is dependent on the sample gas humidity. For example, if the formaldehyde concentration in outdoor air remains constant, but the weather and thus the humidity changes, the measured signal intensity for protonated formaldehyde will change. Established countermeasures against this effect include labor-intensive calibrations at different humidity levels and subsequent data correction, the use of filters or membranes to dry the sample air, which will also trap analytes of interest, and the introduction of excessive amounts of humidity into the PTR reaction region to reduce the relative but not the absolute humidity changes caused by the sample gas, which alters the well-defined ion chemistry and again limits quantification accuracy. Here, we present a novel solution to the humidity dependence problem that comes virtually without any drawbacks, does not require any additional labor by the user, and does not diminish analytes of condensable nature. A target humidity for the PTR reaction region is chosen before the actual measurement. Via the controlled injection of water vapor into the reaction region, the humidity is kept constant throughout the analysis, independent of the sample gas constitution. Therefore, it can be excluded that any changes in the acquired ion signal intensities are artifacts caused by changing sample humidity, and, if required, calibration measurements only have to be performed at one humidity level. We introduce the instrumental adaption necessary for using the novel method and subsequently present proof-of-concept results of measurements in a laboratory, as well as in a ‘real-life’ environment, utilizing two different PTR-MS instruments.

Abstract. Toluene represents a large fraction of anthropogenic emissions and significantly contributes to tropospheric ozone and secondary organic aerosol (SOA) formation. Despite the fact that toluene is one of the most studied aromatic compounds, detailed chemical mechanisms still fail to correctly reproduce the speciation of toluene gaseous and condensed oxidation products. This study aims to elucidate the role of initial experimental conditions in toluene SOA mass loadings and to investigate gas–particle partitioning of its reaction products at different relevant temperatures. Gaseous and particulate reaction products were identified and quantified using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) coupled to a CHemical Analysis of aeRosol ONline (CHARON) inlet. The chemical system exhibited a volatility distribution mostly in the semi-volatile regime. Temperature decrease caused a shift of saturation concentration towards lower values. The CHARON–PTR-ToF-MS instrument identified and quantified approximately 60 %–80 % of the total organic mass measured by an aerosol mass spectrometer. A detailed mechanism for toluene gaseous oxidation was developed based on the Master Chemical Mechanism (MCM) and Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) deterministic mechanisms, modified following the literature. The new mechanism showed improvements in modeling oxidation product speciation with more observed species represented and more representative concentrations compared to the MCM–GECKO-A reference. Tests on partitioning processes, nonideality, and wall losses highlighted the high dependency of SOA formation on the considered processes. Our results underline the fact that volatility is not sufficient to explain the gas–particle partitioning: the organic and the aqueous phases need to be considered as well as the interactions between compounds in the particle phase.

New particle formation (NPF) in the tropical free troposphere (FT) is a globally important source of cloud condensation nuclei, affecting cloud properties and climate. Oxidized organic molecules (OOMs) produced from biogenic volatile organic compounds are believed to contribute to aerosol formation in the tropical FT, but without direct chemical observations. We performed in situ molecular-level OOMs measurements at the Bolivian station Chacaltaya at 5240 m above sea level, on the western edge of Amazonia. For the first time, we demonstrate the presence of OOMs, mainly with 4-5 carbon atoms, in both gas-phase and particle-phase (in terms of mass contribution) measurements in tropical FT air from Amazonia. These observations, combined with air mass history analyses, indicate that the observed OOMs are linked to isoprene emitted from the rainforests hundreds of kilometers away. Based on particle-phase measurements, we find that these compounds can contribute to NPF, at least the growth of newly formed nanoparticles, in the tropical FT on a continental scale. Thus, our study is a fundamental and significant step in understanding the aerosol formation process in the tropical FT.

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN)1–4. However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components. The importance of this mechanism depends on the availability of ammonia, which was previously thought to be efficiently scavenged by cloud droplets during convection. However, surprisingly high concentrations of ammonia and ammonium nitrate have recently been observed in the upper troposphere over the Asian monsoon region5,6. Once particles have formed, co-condensation of ammonia and abundant nitric acid alone is sufficient to drive rapid growth to CCN sizes with only trace sulfate. Moreover, our measurements show that these CCN are also highly efficient ice nucleating particles—comparable to desert dust. Our model simulations confirm that ammonia is efficiently convected aloft during the Asian monsoon, driving rapid, multi-acid HNO3–H2SO4–NH3 nucleation in the upper troposphere and producing ice nucleating particles that spread across the mid-latitude Northern Hemisphere.

We present an electrical mobility classifier for mass-mobility measurements of atmospheric ions. Size segregation coupled with mass spectrometric detection of naturally occurring ions in the atmosphere is challenging due to the low ion concentration. Conventional electrical mobility classifying devices were not yet coupled with mass spectrometry to resolve natural ion composition. This is either due to the insufficient transmission efficiency, or design concepts are incompatible with this application e.g., using high electric fields close to the inlets to push ions from high to low electric potential. Here, we introduce an axial ion mobility classifier, termed AMC, with the aim to achieve higher transmission efficiencies to segregate natural ions at reasonable sizing resolution. Similar, to the recently introduced principle of the high-pass electrical mobility filter (HP-EMF) presented by Bezantakos et al., 2015, and Surawski et al., 2017, ions are classified via an electric field that is opposed to the gas flow direction carrying the ions. Compared to the HP-EMF concept, we make use of sheath flows to improve the size resolution in the sub 3 nm range. With our new design we achieve a sizing resolution of 7 with a transmission efficiency of about 70 %.

Abstract. We present first eddy covariance flux measurements with the PTR3-TOF-MS, a novel proton-transfer-reaction mass-spectrometer (PTR-MS). During three weeks in spring 2016 the instrument recorded 10 Hz BVOC data on top of the SMEAR II tower in Hyytiälä, Finland. Flux and concentration data of isoprene, monoterpenes and sesquiterpenes were compared to the literature. Due to the improved instrument sensitivity and a customized “wall less” inlet design we could detect a number of fluxes of semi-volatile and low volatile organic compounds (SVOC and LVOC) with less than single digit picomol/m2/s values for the first time. These compounds include sesquiterpene oxidation products and diterpenes. Daytime diterpene fluxes were in the range of 0.05 to 0.15 picomol/m2/s, which amounts to about 0.25 % to 0.5 % of the daytime sesquiterpene flux above canopy.

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.

This paper presents our approach for a remotely operated robot-based system to perform analysis tasks of suspicious objects such as luggage, trash cans, and similar items with regards to potential terroristic attacks using C(B)R(N)E (chemical, biological, radioactive, nuclear and explosive) substances in public spaces. To reduce the exposure risk for security forces, an existing robot-based system was equipped with a range of sensors including a high-resolution 3D-RGB scanner, gamma and chemical sensors, additional cameras, and positioning sensors. A flexible and modular sensor framework has been designed and implemented that supports efficient integration of multiple sensors of different kinds. The sensor framework is easily extendable and independent of the sensors, so that new components can be integrated with little effort. Data of all sensors is securely transferred to a base processing unit for fusion and processing. A high-resolution 3D model of the surroundings is enriched by the acquired data of all sensors and visualized to improve the situational awareness during mission operation by better perception of the remote situation.