Observations of Sharp Oxalate Reductions in Stratocumulus Clouds at Variable Altitudes: Organic Acid and Metal Measurements During the 2011 E-PEACE Campaign

This work examines organic acid and metal concentrations in northeastern Pacific Ocean stratocumulus cloudwater samples collected by the CIRPAS Twin Otter between July and August 2011. Correlations between a suite of various monocarboxylic and dicarboxylic acid concentrations are consistent with documented aqueous-phase mechanistic relationships leading up to oxalate production. Monocarboxylic and dicarboxylic acids exhibited contrasting spatial profiles reflecting their different sources; the former were higher in concentration near the continent due to fresh organic emissions. Concentrations of sea salt crustal tracer species, oxalate, and malonate were positively correlated with low-level wind speed suggesting that an important route for oxalate and malonate entry in cloudwater is via some combination of association with coarse particles and gaseous precursors emitted from the ocean surface. Three case flights show that oxalate (and no other organic acid) concentrations drop by nearly an order of magnitude relative to samples in the same vicinity. A consistent feature in these cases was an inverse relationship between oxalate and several metals (Fe, Mn, K, Na, Mg, Ca), especially Fe. By means of box model studies we show that the loss of oxalate due to the photolysis of iron oxalato complexes is likely a significant oxalate sink in the study region due to the ubiquity of oxalate precursors, clouds, and metal emissions from ships, the ocean, and continental sources

Cooperation between Research and Practice in the Late Modernity: Critical Perspectives on Cooperation Structures in Research Learning Communities

Wissenschaft-Praxis-Kooperation in Form von Research Learning Communities (RLCs) gilt als probater Weg für erfolgreiche evidenzbasierte Schulentwicklungsprozesse (Rose et al. 2019). In diesem Sinne arbeiten im Projekt UDIN Wissenschaftler:innen, Lehrpersonen und Studierende an inklusiven digitalen Lernarrangements. In diesem Beitrag werden Strukturen und Praktiken dieser Kooperation in den Blick genommen, um Kommunikationsstrukturen kritisch zu beleuchten. Hierzu werden diese Praktiken in den Kontext der Charakteristik der spätmodernen Gesellschaft (Reckwitz 2017) gestellt und die Arbeitswelt der jeweiligen Bezugssysteme der kooperierenden Akteure (Schule, Wissenschaft, Studium) im Hinblick auf ihre Passung zu projektförmigem Arbeiten in Wissenschaft-Praxis-Kooperationen (in Form von RLCs) betrachtet. Anhand ausgewählter Rekonstruktionen (Dokumentarische Methode) der Gespräche aus den Treffen der RLCs zeigt sich, dass die Verhaftung im Allgemeinen aufseiten der schulischen Akteure dem Anspruch an Projektarbeit – das Besondere, Einzigartige herauszuheben – entgegensteht.Cooperation between research and practice in Research Learning Communities (RLCs) appears to be a well-established way for successful processes of evidence-based school development (Rose et al. 2019). In the research and development project UDIN, scientists, teachers and students work on inclusive, digital learning arrangements. This paper focuses on the structures and practices of this cooperation in order to critically analyse the communication structures. For this purpose, these practices are placed in the context of the characteristics of the Late Modernity (Reckwitz 2017). Following on from this, the working worlds of the cooperating actors (school, science, studies) are considered regarding their fit with project-based work in science-practice collaborations (in the form of RLCs). Based on selected reconstructions (documentary method) of the conversations from the meetings of the RLCs, it becomes apparent that the attachment in general on the part of the school actors is contrary to the claim of project work – to highlight the special, the unique

Is there an aerosol signature of chemical cloud processing?

The formation of sulfate and secondary organic aerosol mass in the aqueous phase (aqSOA) of cloud and fog droplets can significantly contribute to ambient aerosol mass. While tracer compounds give evidence that aqueous-phase processing occurred, they do not reveal the extent to which particle properties have been modified in terms of mass, chemical composition, hygroscopicity, and oxidation state. We analyze data from several field experiments and model studies for six air mass types (urban, biogenic, marine, wild fire biomass burning, agricultural biomass burning, and background air) using aerosol size and composition measurements for particles 13&ndash;850&thinsp;nm in diameter. We focus on the trends of changes in mass, hygroscopicity parameter &kappa;, and oxygen-to-carbon (O&thinsp;∕&thinsp;C) ratio due to chemical cloud processing. We find that the modification of these parameters upon cloud processing is most evident in urban, marine, and biogenic air masses, i.e., air masses that are more polluted than very clean air (background air) but cleaner than heavily polluted plumes as encountered during biomass burning. Based on these trends, we suggest that the mass ratio (Rtot) of the potential aerosol sulfate and aqSOA mass to the initial aerosol mass can be used to predict whether chemical cloud processing will be detectable. Scenarios in which this ratio exceeds Rtot&sim;0.5 are the most likely ones in which clouds can significantly change aerosol parameters. It should be noted that the absolute value of Rtot depends on the considered size range of particles. Rtot is dominated by the addition of sulfate (Rsulf) in all scenarios due to the more efficient conversion of SO2 to sulfate compared to aqSOA formation from organic gases. As the formation processes of aqSOA are still poorly understood, the estimate of RaqSOA is likely associated with large uncertainties. Comparison to Rtot values as calculated for ambient data at different locations validates the applicability of the concept to predict a chemical cloud-processing signature in selected air masses.</p

Oxalic acid in clear and cloudy atmospheres: Analysis of data from International Consortium for Atmospheric Research on Transport and Transformation 2004

Oxalic acid is often the leading contributor to the total dicarboxylic acid mass in ambient organic aerosol particles. During the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign, nine inorganic ions (including SO_4^(2−)) and five organic acid ions (including oxalate) were measured on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter research aircraft by a particle-into-liquid sampler (PILS) during flights over Ohio and surrounding areas. Five local atmospheric conditions were studied: (1) cloud-free air, (2) power plant plume in cloud-free air with precipitation from scattered clouds overhead, (3) power plant plume in cloud-free air, (4) power plant plume in cloud, and (5) clouds uninfluenced by local pollution sources. The aircraft sampled from two inlets: a counterflow virtual impactor (CVI) to isolate droplet residuals in clouds and a second inlet for sampling total aerosol. A strong correlation was observed between oxalate and SO_4^(2−) when sampling through both inlets in clouds. Predictions from a chemical cloud parcel model considering the aqueous-phase production of dicarboxylic acids and SO_4^(2−) show good agreement for the relative magnitude of SO_4^(2−) and oxalate growth for two scenarios: power plant plume in clouds and clouds uninfluenced by local pollution sources. The relative contributions of the two aqueous-phase routes responsible for oxalic acid formation were examined; the oxidation of glyoxylic acid was predicted to dominate over the decay of longer-chain dicarboxylic acids. Clear evidence is presented for aqueous-phase oxalic acid production as the primary mechanism for oxalic acid formation in ambient aerosols

Cloud droplet number closure for tropical convective clouds during the ACRIDICON CHUVA campaign

The main objective of the ACRIDICON-CHUVA campaign in September 2014 was the investigation of aerosol-cloud-interactions in the Amazon Basin. Cloud properties near cloud base of growing convective cumuli were characterized by cloud droplet size distribution measurements using a cloud combination probe and a cloud and aerosol spectrometer. In the current study, an adiabatic parcel model was used to perform cloud droplet number closure studies for several flights in differently polluted air masses

The importance of chemical and microphysical droplet properties for oxidant levels and oxidation rates in clouds (Invited webinar).

International audienc

Are average cloud droplet properties sufficient? - The role of drop-resolved properties for predicting oxidant budgets in the atmospheric multiphase system

International audienc

Average Cloud Droplet Size and Composition: Good Assumptions for Predicting Oxidants in the Atmospheric Aqueous Phase?

Chemical models that describe the atmospheric multiphase (gas/aqueous) system often include detailed kinetic and mechanistic schemes describing chemical reactions in both phases. The present study explores the importance of properties including the chemical composition of droplet populations, such as pH value and iron present in only a few droplets, as well as droplet size and their distribution. It is found that the assumption of evenly distributed iron in all cloud droplets leads to an underestimate by up to 1 order of magnitude of OH concentrations in the aqueous phase, whereas the predicted iron(II)/iron(total) ratio is overestimated by up to a factor of 2. While the sulfate mass formed in cloud droplets is not largely affected by any of the assumptions, the predicted secondary organic aerosol mass varies by an order of magnitude. This sensitivity study reveals that multiphase chemistry model studies should focus not only on chemical mechanism development but also on careful considerations of droplet properties to comprehensively describe the atmospheric multiphase chemical system

The impact of copper and iron distribution on reactive oxygen species concentrations in the atmospheric multiphase system

International audienceRedox reactions transition metal ions (TMI), such as iron and copper, affect the concentrations of reactive oxygen species (ROS) in atmospheric cloud droplets and aqueous aerosol particles. Copper and iron have distinct emission sources resulting in only a small number fraction of cloud condensation nuclei and droplets that contain these metals. The fact that TMI reactions only occur in a small subset of particles and droplets is not taken into account in current multiphase chemistry models that are usually initialized with TMI concentrations derived from bulk sampling.Our previous model studies have shown that model predictions based on bulk iron concentrations may significantly underestimate total OH and HO2 budgets if iron is assumed in all cloud (Ervens, 2022; Khaled et al., 2022). We extend this approach to copper reactions and to reactions between copper and iron ions. We use a multiphase chemistry box model to investigate the importance of the number fraction of TMI-containing particles and droplets and show under which atmospheric conditions detailed information on this parameter is most important. The aim of our study is to identify the impacts of the copper and iron distributions in cloud droplets and aqueous aerosol particles on the total gas and aqueous budgets of OH, HO2, H2O2 and O3 in the multiphase system. Our model results give guidance for measurement needs to further constrain the ROS budgets in the atmosphere