Molecular characterization of ultrafine particles using extractive electrospray time-of-flight mass spectrometry

Publisher Copyright: © 2021 The Author(s).Aerosol particles negatively affect human health while also having climatic relevance due to, for example, their ability to act as cloud condensation nuclei. Ultrafine particles (diameter Dp < 100 nm) typically comprise the largest fraction of the total number concentration, however, their chemical characterization is difficult because of their low mass. Using an extractive electrospray time-of-flight mass spectrometer (EESI-TOF), we characterize the molecular composition of freshly nucleated particles from naphthalene and b-caryophyllene oxidation products at the CLOUD chamber at CERN. We perform a detailed intercomparison of the organic aerosol chemical composition measured by the EESI-TOF and an iodide adduct chemical ionization mass spectrometer equipped with a filter inlet for gases and aerosols (FIGAERO-I-CIMS). We also use an aerosol growth model based on the condensation of organic vapors to show that the chemical composition measured by the EESI-TOF is consistent with the expected condensed oxidation products. This agreement could be further improved by constraining the EESI-TOF compound-specific sensitivity or considering condensed-phase processes. Our results show that the EESI-TOF can obtain the chemical composition of particles as small as 20 nm in diameter with mass loadings as low as hundreds of ng m_3 in real time. This was until now difficult to achieve, as other online instruments are often limited by size cutoffs, ionization/thermal fragmentation and/or semicontinuous sampling. Using real-time simultaneous gas- and particle-phase data, we discuss the condensation of naphthalene oxidation products on a molecular level.Peer reviewe

Impact Of Warm Air Mass Intrusions On Atmospheric Chemistry And Microphysics

Arctic winter is dominated by anthropogenic haze, while pollution transport from mid-latitudes decreases in summertime. As a result, aerosol concentrations reach a maximum in winter and drop to minimum in summer. What happens during the season transition, i.e., during spring, is less studied owing to the difficulty of performing measurements in the high Arctic at this time of year. Warm air mass intrusions are characteristic for springtime and they are harbingers of change, from a dry stable atmosphere to a more dynamic one with precipitation. Such air mass intrusions have been studied from a meteorological and thermodynamic perspective but not yet in full detail from a chemical one. Here, we present first results on microphysical and chemical properties of the Arctic air from observations of warm air mass intrusions during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in April 2020. A full suite of state-of-the-art instrumentation (trace gases concentration, aerosol number size distribution, aerosol mass composition, cloud condensation nuclei) was deployed on the bow of the research vessel Polarstern as part of the MOSAiC expedition for a comprehensive characterization of the chemical and microphysical state of the Arctic atmosphere. In this study, we aim to disentangle the effects of warm air mass intrusions on trace gases concentration as well as on aerosol number, mass and composition. During the first major intrusion episode (April 15 to 16, 2020), ambient temperature increased from -30 oC to roughly 0 oC within 48 hours. The relatively ‘cold’ period in early April was characterized by stagnant northerly winds, hence aged and dry Arctic air masses, where a very stable accumulation mode composed of sulfate and organics with traces of halogens was measured. With the arrival of southerly air masses, the particle number size distribution started featuring several modes and increased concentrations as well as particle growth. Moreover, the trace gas and particle chemical composition significantly changed, featuring methane sulfonic acid in the gas phase and ammonium in the particle phase. Warm air intrusions were also systematically associated with regular ozone levels (non-depleted) which is in line with the absence of halogen signature in particles

The driving factors of new particle formation and growth in the polluted boundary layer

Publisher Copyright: © 2021 Mao Xiao et al.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.Peer reviewe