Journal: Atmospheric Environment: X

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Elsevier

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2590-1621

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2020 - 20253
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Publications 1 - 3 of 3
  • Source identification of the elemental fraction of particulate matter using size segregated, highly time-resolved data and an optimized source apportionment approach
    Item type: Journal Article
    Manousakas, Manousos; Furger, Markus; Daellenbach, Kaspar R.; et al. (2022)
    Atmospheric Environment: X
    Source emissions with high covariance degrade the performance of multivariate models, and often highly-time resolved data is needed to accurately extract the contribution of different emissions. Here, we use highly time-resolved size segregated elemental composition data to apportion the sources of the elemental fraction of PM in Zürich (May 2019–May 2020). For data collection, we have used an ambient metals monitor, Xact 625i, equipped with a sampling inlet alternating between PM2.5 and PM10. By implementing interpolation and a newly proposed uncertainty estimation methodology, it was possible to obtain and use in PMF a combined dataset of PM2.5 and PMcoarse (PM10-2.5) having data from only one instrument. The combination of the inlet switching system, the instrument's high time resolution, and the use of advanced source apportionment approaches yielded improved source apportionment results in terms of the number of identified sources, as the model, additionally to the diurnal and seasonal variation of the dataset, also utilizes the variation from the size segregated data. Thirteen sources of elements were identified, i.e., sea salt (5.4%), biomass burning (7.2%), construction (4.3%), industrial (3.3%), light-duty vehicles (5.4%), Pb (0.7%), Zn (0.7%), dust (22.1%), transported dust (9.5%), sulfates (15.4%), heavy-duty vehicles (17%), railway (6.6%) and fireworks (2.4%). The Covid-19 lockdown effect in PM sources in the area was also quantified. High-intensity events disproportionally affect the PMF solution, and in many cases, they are getting discarded before analysis, removing thus valuable information from the dataset. In this study, a three-step source apportionment approach was used to get a well-resolved unmixed solution when firework data points were included in the analysis. This approach can also be used for other sources and/or events with very high contributions that distort source apportionment analysis. Optimized source apportionment techniques are necessary for effective air pollution monitoring.
  • Photolytic fractionation of seven singly and doubly substituted nitrous oxide isotopocules measured by quantum cascade laser absorption spectroscopy
    Item type: Journal Article
    Kantnerova, Kristyna; Jespersen, Malte F.; Bernasconi, Stefano M.; et al. (2020)
    Atmospheric Environment: X
    There is strong interest in using isotopic analysis to better constrain the budget of atmospheric nitrous oxide (N2O). This interest is supported by emerging instruments that allow analysis of multiply substituted species. We have studied fractionation during UV photolysis of singly and doubly isotopically substituted molecules (isotopocules) of N2O. N2O was photolyzed in an electropolished stainless-steel reactor using a broadband laser-driven light source with bandpass filters. Isotopocule ratios were quantified at different stages of photolysis using a quantum cascade laser absorption spectroscopy (QCLAS) system. Wavelength-dependent fractionation constants were determined using the Rayleigh distillation model. The fractionation constants for photolysis with 200 nm and 214 nm bandpass filters, respectively, for the seven most abundant isotopocules of N2O (after 14N14N16O) are: 14N15N16O (456): (−48.9 ± 7.4) ‰ /(−82.4 ± 22.3) ‰, 15N14N16O (546): (−22.2 ± 5.3) ‰ /(−36.1 ± 19.6) ‰, 14N14N17O (447): (−12.7 ± 4.5) ‰ /(−21.9 ± 15.7) ‰, 14N14N18O (448): (−33.5 ± 12.0) ‰ /(−44.1 ± 29.8) ‰, 14N15N18O (458): (−80.9 ± 6.5) ‰ /(−120.9 ± 23.7) ‰, 15N14N18O (548): (−52.7 ± 10.8) ‰ /(−79.1 ± 28.5) ‰, 15N15N16O (556): (−66.9 ± 9.8) ‰ /(−110.9 ± 27.5) ‰. The fractionation constants determined here for isotopocules 456, 546, 447, 448, and 556 are in agreement with previous theoretical models employed in this study and previous experiments. For 458 and 548, the fractionation constants were determined for the first time, confirming the prediction of more negative fractionation for 15N substitution in the central position. The effect of stratospheric photolysis on the clumped isotope Δ values of tropospheric N2O was found to be modest with Δ458 = (4.0 ± 1.0) ‰, Δ548 = (−4.0 ± 1.0) ‰, and Δ556 = (−1.5 ± 1.0) ‰ at 9% photolysis. Therefore, atmospheric variations of doubly substituted N2O isotopocules will likely be dominated by the characteristics of the N2O sources, which strongly supports their value for source attribution and quantification.
  • Verification of fossil CO₂ emissions from Swiss cement factories using direct and indirect ¹⁴CO₂ measurements
    Item type: Journal Article
    Geissbühler, Dylan; Laemmel, Thomas; Antoni, Mathieu; et al. (2025)
    Atmospheric Environment: X
    Cement production currently emits approximately 8 % of global CO₂. However, the fossil content of these emissions can vary significantly due to methods used to reduce fossil emissions, such as the increased use of alternative fuels. Here, we investigated three CO₂ sampling methods used to analyse ¹⁴CO₂ and estimate the fossil fraction (in terms of F¹⁴C) of emissions from three Swiss cement factories. First, direct stack exhaust gas sampling was conducted at a main study site over 6 months and ¹⁴CO₂ measurements were compared with ¹⁴C values from producer fuel use data. A positive offset in F¹⁴C was observed with theoretical values compared to the measurements. This could be reduced by adjusting the assumed ¹⁴C content of some fuels, particularly shredded wood waste. Second, repeated downwind CO₂ emission plume sampling campaigns were carried out at all sites, allowing for a remote estimation and comparison of their F¹⁴C signatures. These measurements yielded realistic average values but also demonstrated sensitivity to local wind conditions, i.e. wind speed and direction. Lastly, we analysed the bulk ¹⁴C content of tree leaves collected around each site to assess their long-term atmospheric fossil CO₂ exposure. Although the observed ¹⁴C depletion and fossil fraction were generally small (close to uncertainty ranges), trees near the factories consistently showed lower F¹⁴C values than background trees. Direct stack exhaust gas sampling proved to be the most reliable approach for quantifying fossil CO₂ emissions from cement production. Crucially, adjustments made to fuel ¹⁴C contents to match measurements suggested an underestimation of fossil CO₂ emissions from the producer at our main site by more than 2 %.
Publications 1 - 3 of 3