2004, Herrmann, Hartmut, Wiedensohler, Alfred, Mertes, Stephan, Wieprecht, Wolfgang, Jaeschke, Wolfgang, Bächmann, Knut

[no abstract available]

2021, Tilgner, Andreas, Schaefer, Thomas, Alexander, Becky, Barth, Mary, Collett, Jeffrey L., Fahey, Kathleen M., Nenes, Athanasios, Pye, Havala O.T., Herrmann, Hartmut, McNeill, V. Faye

The acidity of aqueous atmospheric solutions is a key parameter driving both the partitioning of semi-volatile acidic and basic trace gases and their aqueous-phase chemistry. In addition, the acidity of atmospheric aqueous phases, e.g., deliquesced aerosol particles, cloud, and fog droplets, is also dictated by aqueous-phase chemistry. These feedbacks between acidity and chemistry have crucial implications for the tropospheric lifetime of air pollutants, atmospheric composition, deposition to terrestrial and oceanic ecosystems, visibility, climate, and human health. Atmospheric research has made substantial progress in understanding feedbacks between acidity and multiphase chemistry during recent decades. This paper reviews the current state of knowledge on these feedbacks with a focus on aerosol and cloud systems, which involve both inorganic and organic aqueous-phase chemistry. Here, we describe the impacts of acidity on the phase partitioning of acidic and basic gases and buffering phenomena. Next, we review feedbacks of different acidity regimes on key chemical reaction mechanisms and kinetics, as well as uncertainties and chemical subsystems with incomplete information. Finally, we discuss atmospheric implications and highlight the need for future investigations, particularly with respect to reducing emissions of key acid precursors in a changing world, and the need for advancements in field and laboratory measurements and model tools.

2020, Zhu, Yanhong, Tilgner, Andreas, Hoffmann, Erik Hans, Herrmann, Hartmut, Kawamura, Kimitaka, Yang, Lingxiao, Xue, Likun, Wang, Wenxing

Despite the high abundance of secondary aerosols in the atmosphere, their formation mechanisms remain poorly understood. In this study, the Master Chemical Mechanism (MCM) and the Chemical Aqueous-Phase Radical Mechanism (CAPRAM) are used to investigate the multiphase formation and processing of secondary aerosol constituents during the advection of air masses towards the measurement site of Mt. Tai in northern China. Trajectories with and without chemical–cloud interaction are modeled. Modeled radical and non-radical concentrations demonstrate that the summit of Mt. Tai, with an altitude of ∼1.5 km a.m.s.l., is characterized by a suburban oxidants budget. The modeled maximum gas-phase concentrations of the OH radical are 3.2×106 and 3.5×106 molec. cm−3 in simulations with and without cloud passages in the air parcel, respectively. In contrast with previous studies at Mt. Tai, this study has modeled chemical formation processes of secondary aerosol constituents under day vs. night and cloud vs. non-cloud cases along the trajectories towards Mt. Tai in detail. The model studies show that sulfate is mainly produced in simulations where the air parcel is influenced by cloud chemistry. Under the simulated conditions, the aqueous reaction of HSO−3 with H2O2 is the major contributor to sulfate formation, contributing 67 % and 60 % in the simulations with cloud and non-cloud passages, respectively. The modeled nitrate formation is higher at nighttime than during daytime. The major pathway is aqueous-phase N2O5 hydrolysis, with a contribution of 72 % when cloud passages are considered and 70 % when they are not. Secondary organic aerosol (SOA) compounds, e.g., glyoxylic, oxalic, pyruvic and malonic acid, are found to be mostly produced from the aqueous oxidations of hydrated glyoxal, hydrated glyoxylic acid, nitro-2-oxopropanoate and hydrated 3-oxopropanoic acid, respectively. Sensitivity studies reveal that gaseous volatile organic compound (VOC) emissions have a huge impact on the concentrations of modeled secondary aerosol compounds. Increasing the VOC emissions by a factor of 2 leads to linearly increased concentrations of the corresponding SOA compounds. Studies using the relative incremental reactivity (RIR) method have identified isoprene, 1,3-butadiene and toluene as the key precursors for glyoxylic and oxalic acid, but only isoprene is found to be a key precursor for pyruvic acid. Additionally, the model investigations demonstrate that an increased aerosol partitioning of glyoxal can play an important role in the aqueous-phase formation of glyoxylic and oxalic acid. Overall, the present study is the first that provides more detailed insights in the formation pathways of secondary aerosol constituents at Mt. Tai and clearly emphasizes the importance of aqueous-phase chemical processes on the production of multifunctional carboxylic acids.

2021, Cox, R. Anthony, Ammann, Markus, Crowley, John N., Griffiths, Paul T., Herrmann, Hartmut, Hoffmann, Erik H., Jenkin, Michael E., McNeill, V. Faye, Mellouki, Abdelwahid, Penkett, Christopher J., Tilgner, Andreas, Wallington, Timothy J.

The term open-air factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties and attributed this to Criegee intermediates formed in the reaction of ozone with alkenes. We have re-evaluated those early experiments applying the current state of knowledge of ozone-alkene reactions. Contrary to previous speculation, neither Criegee intermediates nor the HO radicals formed in their decomposition are directly responsible for the germicidal activity attributed to the OAF. We identify other potential candidates, which are formed in ozone-alkene reactions and have known (and likely) germicidal properties, but the compounds responsible for the OAF remain a mystery. There has been very little research into the OAF since the 1970s, and this effect seems to have been largely forgotten. In this opinion piece we remind the community of the germicidal open-air factor. Given the current global pandemic spread by an airborne pathogen, understanding the natural germicidal effects of ambient air, solving the mystery of the open-air factor and determining how this effect can be used to improve human welfare should be a high priority for the atmospheric science community. © 2021 The Author(s).

2020, Fomba, Khanneh Wadinga, Deabji, Nabil, Barcha, Sayf El Islam, Ouchen, Ibrahim, Elbaramoussi, El Mehdi, El Moursli, Rajaa Cherkaoui, Harnafi, Mimoun, El Hajjaji, Souad, Mellouki, Abdelwahid, Herrmann, Hartmut

Trace metals in ambient particulate matter and cloud are considered key elements of atmospheric processes as they affect air quality, environmental ecosystems, and cloud formation. However, they are often available at trace concentrations in these media such that their analysis requires high-precision and sensitive techniques. In this study, different analytical methods were applied to quantify trace metals in particulate matter (PM) samples collected on quartz and polycarbonate filters as well as cloud water, using the Total reflection X-Ray Fluorescence (TXRF) technique. These methods considered the measurement of filter samples directly without and with chemical pretreatment. Direct measurements involved the analysis of PM samples collected on polycarbonate filters and cloud water samples after they are brought onto TXRF carrier substrates. The chemical treatment method involved the assessment of different acid digestion procedures on PM sampled on quartz filters. The solutions applied were reverse aqua regia, nitric acid, and a combination of nitric acid and hydrogen peroxide. The effect of cold-plasma treatment of samples on polycarbonate filters before TXRF measurements was also investigated. Digestion with the reverse aqua regia solution provided lower blanks and higher recovery in comparison to other tested procedures. The detection limits of the elements ranged from 0.3 to 44 ng cm−2. Ca, K, Zn, and Fe showed the highest detection limits of 44, 35, 6, and 1 ng cm−2, while As and Se had the lowest of 0.3 and 0.8 ng cm−2, respectively. The method showed higher recovery for most trace metals when applied to commercially available reference materials and field samples. TXRF measurements showed good agreement with results obtained from ion chromatography measurements for elements such as Ca and K. Cold-plasma treatment did not significantly lead to an increase in the detected concentration, and the results were element specific. Baking of the quartz filters prior to sampling showed a reduction of more than 20 % of the filter blanks for elements such as V, Sr, Mn, Zn, and Sb. The methods were applied successfully on ambient particulate matter and cloud water samples collected from the Atlas Mohammed V station in Morocco and the Cape Verde Atmospheric Observatory. The obtained concentrations were within the range reported using different techniques from similar remote and background regions elsewhere, especially for elements of anthropogenic origins such as V, Pb, and Zn with concentrations of up to 10, 19, and 28 ng m−3, respectively. Enrichment factor analysis indicated that crustal matter dominated the abundance of most of the elements, while anthropogenic activities also contributed to the abundance of elements such as Sb, Se, and Pb. The results confirm that TXRF is a useful complementary sensitive technique for trace metal analysis of particulate matter in the microgram range as well as in cloud water droplets.

2021, Hartmann, Markus, Gong, Xianda, Kecorius, Simonas, van Pinxteren, Manuela, Vogl, Teresa, Welti, André, Wex, Heike, Zeppenfeld, Sebastian, Herrmann, Hartmut, Wiedensohler, Alfred, Stratmann, Frank

Ice-nucleating particles (INPs) initiate the primary ice formation in clouds at temperatures above ca. -38gC and have an impact on precipitation formation, cloud optical properties, and cloud persistence. Despite their roles in both weather and climate, INPs are not well characterized, especially in remote regions such as the Arctic. We present results from a ship-based campaign to the European Arctic during May to July 2017. We deployed a filter sampler and a continuous-flow diffusion chamber for offline and online INP analyses, respectively. We also investigated the ice nucleation properties of samples from different environmental compartments, i.e., the sea surface microlayer (SML), the bulk seawater (BSW), and fog water. Concentrations of INPs (NINP) in the air vary between 2 to 3 orders of magnitudes at any particular temperature and are, except for the temperatures above -10gC and below -32gC, lower than in midlatitudes. In these temperature ranges, INP concentrations are the same or even higher than in the midlatitudes. By heating of the filter samples to 95gC for 1ĝ€¯h, we found a significant reduction in ice nucleation activity, i.e., indications that the INPs active at warmer temperatures are biogenic. At colder temperatures the INP population was likely dominated by mineral dust. The SML was found to be enriched in INPs compared to the BSW in almost all samples. The enrichment factor (EF) varied mostly between 1 and 10, but EFs as high as 94.97 were also observed. Filtration of the seawater samples with 0.2ĝ€¯μm syringe filters led to a significant reduction in ice activity, indicating the INPs are larger and/or are associated with particles larger than 0.2ĝ€¯μm. A closure study showed that aerosolization of SML and/or seawater alone cannot explain the observed airborne NINP unless significant enrichment of INP by a factor of 105 takes place during the transfer from the ocean surface to the atmosphere. In the fog water samples with -3.47gC, we observed the highest freezing onset of any sample. A closure study connecting NINP in fog water and the ambient NINP derived from the filter samples shows good agreement of the concentrations in both compartments, which indicates that INPs in the air are likely all activated into fog droplets during fog events. In a case study, we considered a situation during which the ship was located in the marginal sea ice zone and NINP levels in air and the SML were highest in the temperature range above -10gC. Chlorophyll a measurements by satellite remote sensing point towards the waters in the investigated region being biologically active. Similar slopes in the temperature spectra suggested a connection between the INP populations in the SML and the air. Air mass history had no influence on the observed airborne INP population. Therefore, we conclude that during the case study collected airborne INPs originated from a local biogenic probably marine source. © Author(s) 2021.

2020, Poulain, Laurent, Spindler, Gerald, Grüner, Achim, Tuch, Thomas, Stieger, Bastian, van Pinxteren, Dominik, Petit, Jean-Eudes, Favez, Olivier, Herrmann, Hartmut, Wiedensohler, Alfred

The aerosol chemical speciation monitor (ACSM) is nowadays widely used to identify and quantify the main components of fine particles in ambient air. As such, its deployment at observatory platforms is fully incorporated within the European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS). Regular intercomparisons are organized at the Aerosol Chemical Monitoring Calibration Center (ACMCC; part of the European Center for Aerosol Calibration, Paris, France) to ensure the consistency of the dataset, as well as instrumental performance and variability. However, in situ quality assurance remains a fundamental aspect of the instrument's stability. Here, we present and discuss the main outputs of long-term quality assurance efforts achieved for ACSM measurements at the research station Melpitz (Germany) since 2012 onwards. In order to validate the ACSM measurements over the years and to characterize seasonal variations, nitrate, sulfate, ammonium, organic, and particle mass concentrations were systematically compared against the collocated measurements of daily offline high-volume PM1 and PM2:5 filter samples and particle number size distribution (PNSD) measurements. Mass closure analysis was made by comparing the total particle mass (PM) concentration obtained by adding the mass concentration of equivalent black carbon (eBC) from the multi-angle absorption photometer (MAAP) to the ACSM chemical composition, to that of PM1 and PM2:5 during filter weighing, as well as to the derived mass concentration of PNSD. A combination of PM1 and PM2:5 filter samples helped identifying the critical importance of the upper size cutoff of the ACSM during such exercises. The ACSM-MAAP-derived mass concentrations systematically deviated from the PM1 mass when the mass concentration of the latter represented less than 60% of PM2:5, which was linked to the transmission efficiency of the aerodynamic lenses of the ACSM. The best correlations are obtained for sulfate (slopeD 0:96; R2 D 0:77) and total PM (slopeD 1:02; R2 D 0:90). Although, sulfate did not exhibit a seasonal dependency, total PM mass concentration revealed a small seasonal variability linked to the increase in non-water-soluble fractions. The nitrate suffers from a loss of ammonium nitrate during filter collection, and the contribution of organo-nitrate compounds to the ACSM nitrate signal make it difficult to directly compare the two methods. The contribution of m=z 44 (f44) to the total organic mass concentration was used to convert the ACSM organic mass (OM) to organic carbon (OC) by using a similar approach as for the aerosol mass spectrometer (AMS). The resulting estimated OCACSM was compared with the measured OCPM1 (slopeD 0:74; R2 D 0:77), indicating that the f44 signal was relatively free of interferences during this period. The PM2:5 filter samples use for the ACSM data quality might suffer from a systematic bias due to a size truncation effect as well as to the presence of chemical species that cannot be detected by the ACSM in coarse mode (e.g., sodium nitrate and sodium sulfate). This may lead to a systematic underestimation of the ACSM particle mass concentration and/or a positive artifact that artificially decreases the discrepancies between the two methods. Consequently, ACSM data validation using PM2:5 filters has to be interpreted with extreme care. The particle mass closure with the PNSD was satisfying (slopeD 0:77; R2 D 0:90 over the entire period), with a slight overestimation of the mobility particle size spectrometer (MPSS)-derived mass concentration in winter. This seasonal variability was related to a change on the PNSD and a larger contribution of the supermicrometer particles in winter. This long-term analysis between the ACSM and other collocated instruments confirms the robustness of the ACSM and its suitability for long-term measurements. Particle mass closure with the PNSD is strongly recommended to ensure the stability of the ACSM. A near-real-time mass closure procedure within the entire ACTRIS-ACSM network certainly represents an optimal quality control and assurance of both warranting the quality assurance of the ACSM measurements as well as identifying cross-instrumental biases. © Author(s) 2020.

2017, Brüggemann, Martin, Poulain, Laurent, Held, Andreas, Stelzer, Torsten, Zuth, Christoph, Richters, Stefanie, Mutzel, Anke, van Pinxteren, Dominik, Iinuma, Yoshiteru, Katkevica, Sarmite, Rabe, René, Herrmann, Hartmut, Hoffmann, Thorsten

The chemical composition of ambient organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in central Europe in July 2014 (Fichtelgebirge – Biogenic Emission and Aerosol Chemistry, F-BEACh 2014). Among several common biogenic secondary organic aerosol (BSOA) marker compounds, 93 acidic oxygenated hydrocarbons were detected with elevated abundances and were thus attributed to be characteristic for the organic aerosol mass at the site. Monoterpene measurements exhibited median mixing ratios of 1.6 and 0.8 ppbV for in and above canopy levels respectively. Nonetheless, concentrations for early-generation oxidation products were rather low, e.g., pinic acid (c  =  4.7 (±2.5) ng m−3). In contrast, high concentrations were found for later-generation photooxidation products such as 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA, c  =  13.8 (±9.0) ng m−3) and 3-carboxyheptanedioic acid (c  =  10.2 (±6.6) ng m−3), suggesting that aged aerosol masses were present during the campaign period. In agreement, HYSPLIT trajectory calculations indicate that most of the arriving air masses traveled long distances (>  1500 km) over land with high solar radiation. In addition, around 47 % of the detected compounds from filter sample analysis contained sulfur, confirming a rather high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were tentatively identified by high-resolution mass spectrometry. Correlations among HOOS, sulfate, and highly oxidized multifunctional organic compounds (HOMs) support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Moreover, periods with high relative humidity indicate that aqueous-phase chemistry might play a major role in HOOS production. However, for dryer periods, coinciding signals for HOOS and gas-phase peroxyradicals (RO2•) were observed, suggesting RO2• to be involved in HOOS formation.

2020, Schaefer, Thomas, Wen, Liang, Estelmann, Arne, Maak, Joely, Herrmann, Hartmut

Rate constants for the aqueous-phase reactions of the hydroxyl radical with the dicarboxylic acids, succinic acid and pimelic acid were determined using the relative rate technique over the temperature range 287 K ≤ T ≤ 318 K and at pH = 2.0, 4.6 or 4.9 and 8.0. OH radicals were generated by H2O2 laser flash photolysis while thiocyanate was used as a competitor. The pH values were adjusted to obtain the different speciation of the dicarboxylic acids. The following Arrhenius expressions were determined (in units of L mol-1 s-1): succinic acid, k(T, AH2) (2.1 x 0.1) ± 1010 exp[(-1530 x 250 K)/T], k(T, AH-) (1.8 x 0.1) ± 1010 exp[(-1070 x 370 K)/T], k(T, A2-) (2.9 x 0.2) ± 1011 exp[(-1830 x 350 K)/T] and pimelic acid, k(T, AH2) (7.3 x 0.2) ± 1010 exp[(-1040 x 140 K)/T], k(T, AH-) (1.8 x 0.1) ± 1011 exp[(-1200 x 240 K)/T], k(T, A2-) (1.4 x 0.1) ± 1012 exp[(-1830 x 110 K)/T]. A general OH radical reactivity trend for dicarboxylic acids was found as k(AH2) < k(AH-) < k(A2-). By using the pH and temperature dependent rate constants, source and sinking processes in the tropospheric aqueous phase can be described precisely. © 2020 by the authors.

2021, Triesch, Nadja, van Pinxteren, Manuela, Engel, Anja, Herrmann, Hartmut

Measurements of free amino acids (FAAs) in the marine environment to elucidate their transfer from the ocean into the atmosphere, to marine aerosol particles and to clouds, were performed at the MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) campaign at the Cabo Verde islands in autumn 2017. According to physical and chemical specifications such as the behavior of air masses, particulate MSA concentrations and MSA=sulfate ratios, as well as particulate mass concentrations of dust tracers, aerosol particles predominantly of marine origin with low to medium dust influences were observed. FAAs were investigated in different compartments: they were examined in two types of seawater underlying water (ULW) and in the sea surface microlayer (SML), as well as in ambient marine size-segregated aerosol particle samples at two heights (ground height based at the Cape Verde Atmospheric Observatory, CVAO, and at 744m height on Mt. Verde) and in cloud water using concerted measurements. The ΣFAA concentration in the SML varied between 0.13 and 3.64 μmol L-1, whereas it was between 0.01 and 1.10 μmol L-1in the ULW; also, a strong enrichment of ΣFAA (EFSML: 1.1-298.4, average of 57.2) was found in the SML. In the submicron (0.05-1.2 μm) aerosol particles at the CVAO, the composition of FAAs was more complex, and higher atmospheric concentrations of ΣFAA (up to 6.3 ngm-3) compared to the supermicron (1.2-10 μm) aerosol particles (maximum of 0.5 ngm-3) were observed. The total ΣFAA concentration (PM10) was between 1.8 and 6.8 ngm-3and tended to increase during the campaign. Averaged ΣFAA concentrations in the aerosol particles on Mt. Verde were lower (submicron: 1.5 ngm-3; supermicron: 1.2 ngm-3) compared to the CVAO. A similar contribution percentage of ΣFAA to dissolved organic carbon (DOC) in the seawater (up to 7.6 %) and to water-soluble organic carbon (WSOC) in the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAAs and DOC in the marine environment. Considering solely ocean-atmosphere transfer and neglecting atmospheric processing, high FAA enrichment factors were found in both aerosol particles in the submicron range (EFaer(ΣFAA):2×103-6×103) and medium enrichment factors in the supermicron range (EFaer(ΣFAA):1×101-3×101). In addition, indications for a biogenic FAA formation were observed. Furthermore, one striking finding was the high and varying FAA cloud water concentration (11.2-489.9 ngm-3), as well as enrichments (EFCW:4×103and 1×104compared to the SML and ULW, respectively), which were reported here for the first time. The abundance of inorganic marine tracers (sodium, methanesulfonic acid) in cloud water suggests an influence of oceanic sources on marine clouds. Finally, the varying composition of the FAAs in the different matrices shows that their abundance and ocean- atmosphere transfer are influenced by additional biotic and abiotic formation and degradation processes. Simple physicochemical parameters (e.g., surface activity) are not sufficient to describe the concentration and enrichments of the FAAs in the marine environment. For a precise representation in organic matter (OM) transfer models, further studies. © 2021 American Institute of Physics Inc.. All rights reserved.