Evaluation of the Sources, Precursors, and Processing of Aerosols at a High-Altitude Tropical Site.

This work presents the results from a set of aerosol- and gas-phase measurements collected during the BIO-MAÏDO field campaign in Réunion between March 8 and April 5, 2019. Several offline and online sampling devices were installed at the Maïdo Observatory (MO), a remote high-altitude site in the Southern Hemisphere, allowing the physical and chemical characterization of atmospheric aerosols and gases. The evaluation of short-lived gas-phase measurements allows us to conclude that air masses sampled during this period contained little or no anthropogenic influence. The dominance of sulfate and organic species in the submicron fraction of the aerosol is similar to that measured at other coastal sites. Carboxylic acids on PM10 showed a significant contribution of oxalic acid, a typical tracer of aqueous processed air masses, increasing at the end of the campaign. This result agrees with the positive matrix factorization analysis of the submicron organic aerosol, where more oxidized organic aerosols (MOOAs) dominated the organic aerosol with an increasing contribution toward the end of the campaign. Using a combination of air mass trajectories (model predictions), it was possible to assess the impact of aqueous phase processing on the formation of secondary organic aerosols (SOAs). Our results show how specific chemical signatures and physical properties of air masses, possibly affected by cloud processing, can be identified at Réunion. These changes in properties are represented by a shift in aerosol size distribution to large diameters and an increased contribution of secondary sulfate and organic aerosols after cloud processing.

Aniline-based catalysts as promising tools to improve analysis of carbonyl compounds through derivatization techniques: preliminary results using dansylacetamidooxyamine derivatization and LC-fluorescence.

Derivatization techniques based on α-effect amines and H+ catalysis are commonly used for the measurement of carbonyl compounds (CCs), whether in environmental, food, or biological samples. Here, we investigated the potential of aniline-based catalysts to improve derivatization rates of selected carbonyls by using dansylacetamidooxyamine (DNSAOA) as a reagent. Kinetic experiments were performed in aqueous solutions by varying catalyst and CC concentrations and delivered insights into the reaction mechanism. Using anilinium acetate (AnAc), rate constants varied linearly with the catalyst concentration with rate enhancements toward H+-catalyzed reactions as high as ca. 90 and 200 for acetone and benzaldehyde, respectively. Owing to contamination problems when using AnAc, anilinium chloride (AnCl) was chosen for the optimized analysis of real samples at low concentration. Rate enhancements for derivatization reaction of 4.4 (methylglyoxal), 6.0 (glyoxal), 12 (acetone), 20 (formaldehyde), and 47 (hydroxyacetaldehyde) were obtained using 0.1 M AnCl. The optimized method was successfully applied to the determination of the above compounds in natural snow and meltwater samples. Limits of detection (LODs) and limits of quantification (LOQs) were in the 2-14 and 7-41 nM range, respectively, i.e., low enough to allow for the analysis of most natural samples. Satisfactory relative recoveries (92.8 ± 3.8-118.3 ± 4.4%) and intra-day precision (2.7-11.3%) were achieved. Finally, we think that this approach could be applied not only to every α-effect nitrogen reagent-with the most evident profit of lowering derivatization times and particularly those required for low-reactive ketones-but also to the derivatization of CCs onto coated solid sorbents.

Sensitive determination of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence.

In this study we improved the dansylacetamidooxyamine (DNSAOA)-LC-fluorescence method for the determination of aqueous-phase glyoxal (GL), methylglyoxal (MG) and hydroxyacetaldehyde (HA). As derivatization of dicarbonyls can potentially lead to complex mixtures, a thorough study of the reaction patterns of GL and MG with DNSAOA was carried out. Derivatization of GL and MG was shown to follow the kinetics of successive reactions, yielding predominantly doubly derivatized compounds. We verified that the bis-DNSAOA structure of these adducts exerted only minor influence on their fluorescence properties. Contrary to observations made with formaldehyde, derivatization of GL, MG and, to a lesser extent of HA, was shown to be faster in acidic (H(2)SO(4)) medium with a maximum of efficiency for acid concentrations of ca. 2.5 mM. Concomitant separation of GL, MG, HA and of single carbonyls was achieved within 20 min by using C(18) chromatography and a gradient of CH(3)CN in water. Detection limits of 0.27, 0.17 and 0.12 nM were determined for GL, MG and HA, respectively. Consequently, low sample volumes are sufficient and, unlike numerous published methods, neither preconcentration nor large injection volumes are necessary to monitor trace-level samples. The method shows relative measurement uncertainties better than ±15% at the 95% level of confidence and good dynamic ranges (R(2)>0.99) from 0.01 to 1.5 µM for all carbonyls. GL, MG and HA were identified for the first time in polar snow samples, but also in saline frost flowers for which unexpected levels of 0.1-0.6 µM were measured. Concentrations in the 0.02-2.3 µM range were also measured in cloud water. In most samples, a predominance of HA over GL and MG was observed.

Thermodynamics of the formaldehyde-water and formaldehyde-ice systems for atmospheric applications.

Formaldehyde (HCHO) is a species involved in numerous key atmospheric chemistry processes that can significantly impact the oxidative capacity of the atmosphere. Since gaseous HCHO is soluble in water, the water droplets of clouds and the ice crystals of snow exchange HCHO with the gas phase and the partitioning of HCHO between the air, water, and ice phases must be known to understand its chemistry. This study proposes thermodynamic formulations for the partitioning of HCHO between the gas phase and the ice and liquid water phases. A reanalysis of existing data on the vapor-liquid equilibrium has shown the inadequacy of the Henry's law formulation, and we instead propose the following equation to predict the mole fraction of HCHO in liquid water at equilibrium, X(HCHO,liq), as a function of the partial pressure P(HCHO) (Pa) and temperature T (K): X(HCHO,liq) = 1.700 × 10(-15) e((8014/T))(P(HCHO))(1.105). Given the paucity of data on the gas-ice equilibrium, the solubility of HCHO and the diffusion coefficient (D(HCHO)) in ice were measured by exposing large single ice crystals to low P(HCHO). Our recommended value for D(HCHO) over the temperature range 243-266 K is D(HCHO) = 6 × 10(-12) cm(2) s(-1). The solubility of HCHO in ice follows the relationship X(HCHO,ice) = 9.898 × 10(-13) e((4072/T))(P(HCHO))(0.803). Extrapolation of these data yields the P(HCHO) versus 1/T phase diagram for the H(2)O-HCHO system. The comparison of our results to existing data on the partitioning of HCHO between the snow and the atmosphere in the high arctic highlights the interplay between thermodynamic equilibrium and kinetics processes in natural systems.