SEASONAL VARIABILITY OF AEROSOL COMPOSITION IN SWITZERLAND: A MODELLING STUDY

In this study, we applied the MM5/CAMx model system over Switzerland for winter and summer periods in 2006. The focus is on the formation and transport of aerosols and the contribution of various sources to the aerosol formation both in winter and summer seasons. Our model system uses three nested domains with 27 km (Europe), 9 km (central Europe) and 3 km (Switzerland) resolutions. The concentrations of aerosol components are calculated for particle sizes smaller than 2.5 μm. The model’s capability to reproduce the aerosol concentrations is investigated by comparing the model results with the measurements performed during the same periods. In general, the modelled concentrations of inorganic aerosols agree quite well with the AMS measurements, whereas organic aerosols are underestimated. The chemical composition of aerosols in summer differs from that in winter. Both measurements and model predictions indicate that organic aerosols and particulate nitrate are the major components of the winter aerosol composition in Switzerland. In summer, organic aerosols dominate the aerosol composition and they are mostly secondary organic aerosols formed from the biogenic precursors. Recent measurements suggest that wood-burning emissions might contribute significantly to the aerosol concentrations, especially in winter. The lack of wood burning emissions in emission inventory could cause partly the underestimation of organic aerosols. The secondary organic aerosol (SOA) formation will be soon improved by using a new model version where oligomerization and SOA formation from isoprene and sesquiterpenes are implemented

SEASONAL VARIABILITY OF AEROSOL COMPOSITION IN SWITZERLAND: A MODELLING STUDY

In this study, we applied the MM5/CAMx model system over Switzerland for winter and summer periods in 2006. The focus is on the formation and transport of aerosols and the contribution of various sources to the aerosol formation both in winter and summer seasons. Our model system uses three nested domains with 27 km (Europe), 9 km (central Europe) and 3 km (Switzerland) resolutions. The concentrations of aerosol components are calculated for particle sizes smaller than 2.5 μm. The model’s capability to reproduce the aerosol concentrations is investigated by comparing the model results with the measurements performed during the same periods. In general, the modelled concentrations of inorganic aerosols agree quite well with the AMS measurements, whereas organic aerosols are underestimated. The chemical composition of aerosols in summer differs from that in winter. Both measurements and model predictions indicate that organic aerosols and particulate nitrate are the major components of the winter aerosol composition in Switzerland. In summer, organic aerosols dominate the aerosol composition and they are mostly secondary organic aerosols formed from the biogenic precursors. Recent measurements suggest that wood-burning emissions might contribute significantly to the aerosol concentrations, especially in winter. The lack of wood burning emissions in emission inventory could cause partly the underestimation of organic aerosols. The secondary organic aerosol (SOA) formation will be soon improved by using a new model version where oligomerization and SOA formation from isoprene and sesquiterpenes are implemented

Impact of meteorological conditions on airborne fine particle composition and secondary pollutant characteristics in urban area during winter-time

The assessment of airborne fine particle composition and secondary pollutant characteristics in the case of Augsburg, Germany, during winter (31 January–12 March 2010) is studied on the basis of aerosol mass spectrometry (3 non-refractory components and organic matter, 3 positive matrix factorizations (PMF) factors), particle size distributions (PSD, 5 size modes, 5 PMF factors), further air pollutant mass concentrations (7 gases and VOC, black carbon, PM10, PM2.5) and meteorological measurements, including mixing layer height (MLH), with one-hourly temporal resolution. Data were subjectively assigned to 10 temporal phases which are characterised by different meteorological influences and air pollutant concentrations. In each phase hierarchical clustering analysis with the Ward method was applied to the correlations of air pollutants, PM components, PM source contributions and PSD modes and correlations of these data with all meteorological parameters. This analysis resulted in different degrees of sensitivities of these air pollutant data to single meteorological parameters. It is generally found that wind speed (negatively), MLH (negatively), relative humidity (positively) and wind direction influence primary pollutant and accumulation mode particle (size range 100–500 nm) concentrations. Temperature (negatively), absolute humidity (negatively) and also relative humidity (positively) are relevant for secondary compounds of PM and particle (PM2.5, PM10) mass concentrations. NO, nucleation and Aitken mode particle and the fresh traffic aerosol concentrations are only weakly dependent on meteorological parameters and thus are driven by emissions. These daily variation data analyses provide new, detailed meteorological influences on air pollutant data with the focus on fine particle composition and secondary pollutant characteristics and can explain major parts of certain PM component and gaseous pollutant exposure

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

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

Characterization of Gas-Phase Organics Using Proton TransferReaction Time-of-Flight Mass Spectrometry: Aircraft Turbine Engines

Nonmethane organic gas emissions (NMOGs) from in-service aircraft turbine engines were investigated using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) at an engine test facility at Zurich Airport, Switzerland. Experiments consisted of 60 exhaust samples for seven engine types (used in commercial aviation) from two manufacturers at thrust levels ranging from idle to takeoff. Emission indices (EIs) for more than 200 NMOGs were quantified, and the functional group fractions (including acids, carbonyls, aromatics, and aliphatics) were calculated to characterize the exhaust chemical composition at different engine operation modes. Total NMOG emissions were highest at idling with an average EI of 7.8 g/kg fuel and were a factor of &sim;40 lower at takeoff thrust. The relative contribution of pure hydrocarbons (particularly aromatics and aliphatics) of the engine exhaust decreased with increasing thrust while the fraction of oxidized compounds, for example, acids and carbonyls increased. Exhaust chemical composition at idle was also affected by engine technology. Older engines emitted a higher fraction of nonoxidized NMOGs compared to newer ones. Idling conditions dominated ground level organic gas emissions. Based on the EI determined here, we estimate that reducing idle emissions could substantially improve air quality near airports

Particle-phase processing of alpha-pinene NO3 secondary organic aerosol in the dark

The NO3 radical represents a significant nighttime oxidant which is present downstream of polluted environments. Existing studies have investigated the formation of secondary organic aerosol (SOA) from NO3 radicals, focusing on the yields, general composition, and hydrolysis of organonitrates; however, there is limited knowledge about how the composition of NO3-derived SOA evolves as a result of particle-phase reactions. Here, SOA was formed from the reaction of alpha-pinene with NO3 radicals generated from N2O5, and the resulting SOA was aged in the dark. The initial composition of NO3-derived alpha-pinene SOA was slightly dependent upon the concentration of N2O5 injected (excess of NO3 or excess of alpha-pinene) but was largely dominated by dimer dinitrates (C20H32N2O8-13). Oxidation reactions (e.g., C20H32N2O8 -> C20H32N2O9 -> C20H32N2O10) accounted for 60 %-70 % of the particle-phase reactions observed. Fragmentation reactions and dimer degradation pathways made up the remainder of the particle-phase processes occurring. The exact oxidant is not known, although suggestions are offered (e.g., N2O5, organic peroxides, or peroxynitrates). Hydrolysis of -ONO2 functional groups was not an important loss term during dark aging under the relative humidity conditions of our experiments (58 %-62 %), and changes in the bulk organonitrate composition were likely driven by evaporation of highly nitrogenated molecules. Overall, 25 %-30 % of the particle-phase composition changes as a function of particle-phase reactions during dark aging, representing an important atmospheric aging pathway.ISSN:1680-7375ISSN:1680-736

Characterizing the sources of ambient PM10 organic aerosol in urban and rural Catalonia, Spain

Organic aerosols (OA) have recently been shown to be the dominant contributor to the oxidative potential of airborne particulate matter in northeastern Spain. We collected PM10 filter samples every fourth day from January 2017 to March 2018 at two sampling stations located in Barcelona city and Montseny Natural Park, representing urban and rural areas, respectively. The chemical composition of PM10 was analyzed offline using a broad set of analytical instruments, including high-resolution time-of-flight mass spectrometry (HR-ToF-AMS), a total organic carbon analyzer (TCA), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), ion chromatography (IC), and thermal-optical carbon analyzer. Source apportionment analysis of the water-soluble organic content of the samples measured via HR-ToF-AMS revealed two primary and two secondary sources of OA, which included biomass-burning OA (BBOA), sulfur-containing OA (SCOA), as well as summer- and winter‑oxygenated OA (SOOA and WOOA). The presence of hydrocarbon-like water-insoluble OA was also identified based on concentration trends in black carbon and nitrogen oxides. The results from the source apportionment analysis of the inorganic composition were correlated with different OA factors to assess potential source contributors. Barcelona showed significantly higher average water-soluble OA concentrations (5.63 ± 0.56 μg m-3) than Montseny (3.27 ± 0.37 μg m-3) over the sampling period. WOOA accounted for nearly 27 % of the averaged OA in Barcelona compared to only 7 % in Montseny. In contrast, SOOA had a greater contribution to OA in Montseny (47 %) than in Barcelona (24 %). SCOA and BBOA were responsible for 15–28 % of the OA at both sites. There were also seasonal variations in the relative contributions of different OA sources. Our overall results showed that local anthropogenic sources were primarily responsible for up to 70 % of ambient soluble OA in Barcelona, and regulating local-scale emissions could significantly improve air quality in urban Spain

High-frequency gaseous and particulate chemical characterization using extractive electrospray ionization mass spectrometry (Dual-Phase-EESI-TOF)

To elucidate the sources and chemical reaction pathways of organic vapors and particulate matter in the ambient atmosphere, real-time detection of both the gas and particle phase is needed. State-of-the-art techniques often suffer from thermal decomposition, ionization-induced fragmentation, high cut-off size of aerosols or low time resolution. In response to all these limitations, we developed a new technique that uses extractive electrospray ionization (EESI) for online gas and particle chemical speciation, namely the dual-phase extractive electrospray ionization time-of-flight mass spectrometer (Dual-Phase-EESI-TOF or Dual-EESI for short). The Dual-EESI was designed and optimized to measure gas- and particle-phase species with saturation vapor concentrations spanning more than 10 orders of magnitude with good linearity and a measurement cycle as fast as 3 min. The gas-phase selectivity of the Dual-EESI was compared with that of nitrate chemical ionization mass spectrometry. In addition, we performed organic aerosol uptake experiments to characterize the relative gas and particle response factors. In general, the Dual-EESI is more sensitive toward gas-phase analytes as compared to their particle-phase counterparts. The real-time measurement capability of the Dual-EESI for chemically speciated gas- and particle-phase measurements can provide new insights into aerosol sources or formation mechanisms, where gas-particle partitioning behavior can be determined after absolute parameterization of the gas / particle sensitivity.ISSN:1867-1381ISSN:1867-854