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Stable 15N isotopes in fine and coarse urban particulate matter
2021, Wiedenhaus, Hanna, Ehrnsperger, Laura, Klemm, Otto, Strauss, Harald
Particulate nitrogen has far-reaching negative effects on human health and the environment, and effective strategies for reducing it require understanding its sources and formation processes. To learn about these factors, we recorded size-resolved nitrogen isotope ratios (Ī“15N) of total particulate N at an urban site in northwest Germany during a four-week measuring campaign. We observed a steady decrease in Ī“15N when going from fine to coarse particles, with values between +18 ā° and ā2 ā°. This difference based on particle size is caused by different isotope fractionation processes during particle formation: The fine particles contain ammonium nitrate, which is formed in an equilibrium process, leading to an enrichment of 15N. Moreover, fine particles are more reactive due to their larger surface areas and relatively long residence times in the atmosphere, which leads to an additional enrichment of 15N; a key step of this process likely occurs when the ammonium particles interact with ammonia from agricultural sources. In contrast to fine particles, coarse particles are formed by direct absorption of HNO3 on preexisting particles; the HNO3 stems from traffic emissions of NOx and subsequent oxidation in the atmospheric gas phase. Because only a small amount of isotope fractionation is associated with non-equilibrium processes during phase transitions, there is less 15N enrichment in the coarse particles. Overall, nitrogen isotopes clearly reflect the different formation processes of fine and coarse aerosol particles. Ā© 2021 The Author(s). Published with license by Taylor & Francis Group, LLC.
The second ACTRIS inter-comparison (2016) for Aerosol Chemical Speciation Monitors (ACSM): Calibration protocols and instrument performance evaluations
2019, Freney, Evelyn, Zhang, Yunjiang, Croteau, Philip, Amodeo, Tanguy, Williams, Leah, Truong, FranƧois, Petit, Jean-Eudes, Sciare, Jean, Sarda-Esteve, Roland, Bonnaire, Nicolas, Arumae, Tarvo, Aurela, Minna, Bougiatioti, Aikaterini, Mihalopoulos, Nikolaos, Coz, Esther, Artinano, BegoƱa, Crenn, Vincent, Elste, Thomas, Heikkinen, Liine, Poulain, Laurent, Wiedensohler, Alfred, Herrmann, Hartmut, Priestman, Max, Alastuey, Andres, Stavroulas, Iasonas, Tobler, Anna, Vasilescu, Jeni, Zanca, Nicola, Canagaratna, Manjula, Carbone, Claudio, Flentje, Harald, Green, David, Maasikmets, Marek, Marmureanu, Luminita, Cruz Minguillon, Maria, Prevot, Andre S.H., Gros, Valerie, Jayne, John, Favez, Olivier
This work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of m/z 44 from organic aerosol. This effect was quantified by the m/z (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an āovercorrectionā of the f44 (m/z 44/Org) signal. This correction based on measurements made with pure NH4NO3, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH4NO3 mixing ratios (from solutions of NH4NO3 and (NH4)2SO4) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO3 mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry. Ā© 2019, Ā© 2019 Author(s). Published with license by Taylor & Francis Group, LLC.