Analysis of Aerosol in Zurich by Infrared Spectroscopy and Statistical Modelling

Atmospheric particulate matter (PM) has been associated with increased morbidity and mortality, reduced visibility, and is one of the least understood components of the climate system. We use the Fourier transform infrared (FT-IR) absorbance spectra of atmospheric aerosol (PM2.5) collected on Teflon filters to characterize the aerosol chemical composition using the functional group (FG) representation. Teflon filters have been collected daily at the National Air Pollution Monitoring Network (NABEL) station in Zurich (Switzerland) from the 1st of April 2016 until the 31st of March 2017. We quantify alcohol COH, carboxylic COOH, alkane CH, carbonyl CO, and amine NH functional groups of the ambient samples by fitting individual Gaussian line shapes to spectra. We compare our analysis with collocated black carbon measurements (BC) that have been apportioned to traffic emission and wood burning

Measurement report: Ice-nucleating particles active ≥ -15 °C in free tropospheric air over western Europe

Ice-nucleating particles (INPs) initiate ice formation in supercooled clouds, typically starting in western Europe at a few kilometres above the ground. However, little is known about the concentration and composition of INPs in the lower free troposphere (FT). Here, we analysed INPs active at −10 ∘C (INP−10) and −15 ∘C (INP−15) that were collected under FT conditions at the high-altitude observatory Jungfraujoch between January 2019 and March 2021. We relied on continuous radon measurements to distinguish FT conditions from those influenced by the planetary boundary layer. Median concentrations in the FT were 2.4 INP−10 m−3 and 9.8 INP−15 m−3, with a multiplicative standard deviation of 2.0 and 1.6 respectively. A majority of INPs were deactivated after exposure to 60 ∘C; thus, they probably originated from certain epiphytic bacteria or fungi. Subsequent heating to 95 ∘C deactivated another 15 % to 20 % of the initial INPs, which were likely other types of fungal INPs that might have been associated with soil organic matter or with decaying leaves. Very few INP−10 withstood heating to 95 ∘C, but on average 20 % of INP−15 in FT samples did so. This percentage doubled during Saharan dust intrusions, which had practically no influence on INP−10. Overall, the results suggest that aerosolised epiphytic microorganisms, or parts thereof, are responsible for the majority of primary ice formation in moderately supercooled clouds above western Europe

Inter-comparison of four different carbon monoxide measurement techniques and evaluation of the long-term carbon monoxide time series of Jungfraujoch

Despite the importance of carbon monoxide (CO) for the overall oxidative capacity of the atmosphere, there is still considerable uncertainty in ambient measurements of CO. To address this issue, an inter-comparison between four different measurement techniques was made over a period of two months at the high-alpine site Jungfraujoch (JFJ), Switzerland. The measurement techniques were Non-dispersive Infrared Absorption (NDIR), Vacuum UV Resonance Fluorescence (VURF), gas chromatographic separation with a mercuric oxide reduction detector (GC/HgO), and gas chromatographic separation followed by reduction on a nickel catalyst and analysis by a flame ionization detector (GC/FID). The agreement among all techniques was better than 2% for one-hourly averages, which confirmed the suitability of the NDIR method for CO measurements even at remote sites. The inter-comparison added to the validation of the 12-year record (1996–2007) of continuous CO measurements at JFJ. To date this is one of the longest time series of continuous CO measurements in the free troposphere over Central Europe. This data record was further investigated with a focus on trend analysis. A significant negative trend was observed at JFJ showing a decrease of 21.4±0.3% over the investigated period, or an average annual decrease of 1.78%/yr (2.65±0.04 ppb/yr). These results were compared with emission inventory data reported to the Long-range Transboundary Air Pollution (LRTAP) Convention. It could be shown that long range transport significantly influences the CO levels observed at JFJ, with air masses of non-European origin contributing at least one third of the observed mole fractions.ISSN:1680-7375ISSN:1680-736

Ice Nucleating Particle Concentrations Increase When Leaves Fall in Autumn

Ice nucleating particles active at −8 °C or warmer (INP−8) are produced by plants and by microorganisms living from and on them. Laboratory studies have shown that large numbers of INP−8 are produced by decaying leaves. At three widely dispersed locations in Northwestern Eurasia, we saw, from an analysis of PM10 filter samples, that seasonal median concentrations of INP−8 in the boundary layer doubled from summer to autumn. Concentrations of INP−8 increased in autumn soon after the normalized differential vegetation index had started to decrease. Whether the large-scale phenological event of leaf senescence and shedding in autumn has an impact on ice formation in clouds is a justified question

A High-Precision Mid-Infrared Spectrometer for Ambient HNO₃ Measurements

Precise and accurate measurements of ambient HNO3 are crucial for understanding various atmospheric processes, but its ultra-low trace amounts and the high polarity of HNO3 have strongly hindered routine, widespread, direct measurements of HNO3 and restricted field studies to mostly short-term, localized measurement campaigns. Here, we present a custom field-deployable direct absorption laser spectrometer and demonstrate its analytical capabilities for in situ atmospheric HNO3 measurements. Detailed laboratory characterizations with a particular focus on the instrument response under representative conditions for tropospheric measurements, i.e., the humidity, spectral interference, changing HNO3 amount fractions, and air-sampling-related artifacts, revealed the key aspects of our method: (i) a good linear response (R2 > 0.98) between 0 and 25 nmol·mol−1 in both dry and humid conditions with a limit of detection of 95 pmol·mol−1; (ii) a discrepancy of 20% between the spectroscopically derived amount fractions and indirect measurements using liquid trapping and ion chromatography; (iii) a systematic spectral bias due to water vapor. The spectrometer was deployed in a three-week field measurement campaign to continuously monitor the HNO3 amount fraction in ambient air. The measured values varied between 0.1 ppb and 0.8 ppb and correlated well with the daily total nitrates measured using a filter trapping method

Atmospheric ice nuclei at the high-altitude observatory Jungfraujoch, Switzerland

The state of a slightly supercooled ephemeral cloud can be changed by the presence of a few particles capable of catalysing freezing, and potentially result in precipitation. We investigated the atmospheric abundance of particles active as ice nuclei at -8 degrees C (IN-8) over the course of a year at the high-alpine station Jungfraujoch (3580 m.a.s.l., Switzerland) through the use of immersion freezing assays of particles collected on quartz micro-fibre filters. In addition, we determined IN-8 on a hill in the planetary boundary layer 95 km northwest of Jungfraujoch and in the dust laden Saharan Air Layer reaching Tenerife. Results indicate a strong seasonality of IN-8 at Jungfraujoch. Values were largest during summer (between 1 and 10 m(-3)) and about two orders of magnitude smaller during winter. Sahara dust events had a negligible influence on IN-8 at Jungfraujoch. Seasonality in the boundary layer was not observed in the upper, but in the lower bound of IN-8 values. Values <1m(-3) were only found on cold winter days, when IN-8 were more likely to have already been activated and deposited than on warmer days. A good correlation between IN-8 and maximum daily temperature at Jungfraujoch (R-2 = 0.54) suggests IN-8 abundance at Jungfraujoch may be limited most of the year by microphysical processing related to IN activation in approaching air masses

Latrine und Mörtelmischmaschine. Hochmittelalterliche Befunde und Funde der Grabung Martinsgasse 6+8, Basel

Durch die gut erhaltene Schichtabfolge und die aussergewöhnlichen Befunde und Funde ist die Grabung Martinsgasse 6+8 eine Schlüsselstelle für die mittelalterliche Stadtgeschichte Basels. Einer der frühesten nördlich der Alpen nachgewiesenen Latrinenschächte aus dem 7.–9. Jh. und ein mechanischer Mörtelmischer aus dem 9.–11. Jh. sind herausragende Einzelbefunde, die hier im baulichen Kontext vorgestellt werden. Die Kombination von archäologischen Methoden wie Stratigrafie und Typologie mit naturwissenschaftlichen Herangehensweisen wie Radiokarbondatierung, Mikromorphologie, Archäobiologie und Anthropologie erlaubt es, in den «dark earth»-Schichten und in der Flut römischen Altmaterials, mittelalterliche Nutzungs- und Bauhorizonte zu erkennen, zu datieren und zu charakterisieren. Dabei ergeben sich detaillierte Einblicke und wichtige neue Erkenntnisse zum Wandel von Ernährungsweise, Vorratshaltung und Bautechnologie am Übergang von Spätantike zum Mittelalter