Arctic fog chemistry induces the unexpected growth of Aitken mode particles to CCN-active particles

<p>New particle formation (NPF) and early growth are efficient processes producing high concentrations of cloud condensation nuclei (CCNs) precursors in the Arctic marine boundary layer (AMBL). However, due to short lifetime and lack of condensable vapors, newly formed particles do often not grow beyond 50 nm and cause low CCN particle concentrations in the AMBL. Thus, even the smallest amount of Aitken mode particle growth is capable to significantly increase the CCN budget. However, the growth mechanism of Aitken-mode particles from NPF into CCN range in the Arctic is still rather unclear and was therefore investigated during the cruise campaign PASCAL in 2017.</p> <p>During PASCAL, aerosol particles measurements were performed and an unexpected rapid growth of Aitken mode particles was observed right after fog episodes. Combined field data analyses and detailed multiphase chemistry box model simulations with the CAPRAM mechanism were performed to study the underlying processes. Resulting, a new mechanism is proposed explaining how particles with d < 50 nm are able to grow into CCN size range in the Arctic without requiring high water vapor supersaturation (SS). The investigations demonstrated that the rapid post-fog particle growth of Aitken mode is related to chemical processes within the Arctic fog. The redistribution of semi-volatile acidic (e.g., methanesulfonic acid) and basic (e.g., ammonia) compounds from processed CCN-active particles to smaller CCN-inactive particles can cause a rapid particle growth of Aitken mode particles after fog evaporation enabling them to grow towards CCN size. Comparisons of the model results with Berner impactor measurements supports the proposed growth mechanism.</p> <p>Overall, this study provided new insights on how the increasing frequency of NPF and fog-related particle processing can increase in the number of CCNs and cloud droplets leading to an increased albedo of Arctic clouds and thus affect the radiative balance in the Arctic. Since fogs will occur more frequently in the Arctic as a result of climate change, this growth mechanism and a deeper knowledge on its feedbacks can be essential to understand Arctic warming.</p>

Strong deviations from thermodynamically expected phase partitioning of organic acids during one year of rural field measurements

<p>Organic acids are ubiquitous compounds in the troposphere and can affect human health, the climate, air quality, and the linked ecosystems. Depending on their solubility and volatility, they can partition in both gas phase and in the particle phase. In the particle phase, organic acids partly represent about 10% of the water-soluble organic matter. However, their partitioning between different phases is not fully understood yet. Therefore, an upgraded monitor for aerosols and gases in ambient air (MARGA) was applied for one year at the Central European TROPOS research site Melpitz to study the gas- and particle-phase partitioning of formic, acetic, propionic, butyric, glycolic, pyruvic, oxalic, malonic, succinic, malic, and methanesulfonic acid (MSA). Measured gas- and PM<sub>10</sub> particle-phase mean concentrations were 12−445 and 7−31 ng m<sup>-3</sup> for monocarboxylic acids (MCAs), between 0.6−8 and 4−31 ng m<sup>-3</sup> for dicarboxylic acids (DCAs), and 2 and 31 ng m<sup>-3</sup> for MSA, respectively. Assuming full dissolution in nonideal aerosol solutions, empirical noneffective Henry’s law constants (H<sub>emp</sub>) were calculated and compared with literature values (H<sub>lit</sub>). Calculated mean H<sub>emp</sub> were 4.5 × 10<sup>9</sup>−2.2 × 10<sup>10</sup> mol L<sup>−1</sup> atm<sup>−1</sup> for MCAs, 3.6 × 10<sup>10</sup>−7.5 × 10<sup>11</sup> mol L<sup>−1</sup> atm<sup>−1</sup> for DCAs, and 7.5 × 10<sup>7</sup> mol L<sup>−1</sup> atm<sup>−1</sup> for MSA and, thus, factors of 5.1 × 10<sup>3</sup>−9.1 × 10<sup>5</sup> and 2.5−20.3 higher than their corresponding H<sub>lit</sub> for MCAs and DCAs, respectively, and 9.0 × 10<sup>−5</sup> lower than H<sub>lit,MSA</sub>. Data analyses and thermodynamic calculations implicate that the formation of chemical association complexes and organic salts inhibits the partitioning of organic acids toward the gas phase and, thus, at least partly explains higher H<sub>emp</sub> values for both MCAs and summertime DCAs. Low H<sub>emp,MSA</sub> are also unexpected because of the high MSA solubility and are reported for the first time in this study. Overall, the results of the present study implicate that processes responsible for the observed stronger partitioning of carboxylic acids toward the particle phase need to be further investigated and accounted for in complex multiphase chemistry models as they affect the contribution of organic acids to secondary organic aerosol mass, their chemical processing, and lifetime.</p> <p> </p> <p> </p>

A Mechanistic Study on the Formation of Dronic Acids

Dronic acid derivatives, important drugs against bone diseases, may be synthesized from the corresponding substituted acetic acid either by reaction with phosphorus trichloride in methanesulfonic acid as the solvent or by using also phosphorous acid as the P-reactant if sulfolane is applied as the medium. The energetics of the two protocols were evaluated by high-level quantum chemical calculations on the formation of fenidronic acid and benzidronic acid. The second option, involving (HO)2P‑O‑PCl2 as the nucleophile, was found to be more favorable over the first variation, comprising Cl2P‑O‑SO2Me as the real reagent, especially for the case of benzidronate.

Hydrohalogenation of Unactivated Alkenes Using a Methanesulfonic Acid/Halide Salt Combination

The hydrochlorination, hydrobromination, and hydroiodination of unactivated alkenes using methanesulfonic acid and inorganic halide salts (CaCl2, LiBr, LiI) in acetic acid are reported. This approach uses readily available and inexpensive reagents to provide the alkyl halides in up to 99% yield. An example of deuteriochlorination using deuterated acetic acid as the solvent is also demonstrated.

The Role of Organic Acids in New Particle Formation from Methanesulfonic Acid and Methylamine

Atmospheric organic acids (OAs) are expected to enhance methanesulfonic acid (MSA)-driven new particle formation (NPF). However, the exact role of OAs in MSA-driven NPF remains unclear. Here, we employed a two-step strategy to probe the role of OAs in MSA-methylamine (MA) NPF. Initially, we evaluated the enhancing potential of 12 commonly detected OAs in ternary MA-MSA-OA cluster formation by considering the formation free energies of the (MSA)1(MA)1(OA)1 clusters and the atmospheric concentrations of the OAs. It was found that formic acid (ForA) has the highest potential to stabilize the MA-MSA clusters. The high enhancing potential of ForA results from its acidity, structural factors such as no intramolecular H-bonds and high atmospheric abundance. The second step is to extend the MSA-MA-ForA system to larger cluster sizes. The results indicate that ForA can indeed enhance MSA-MA NPF at atmospheric conditions (the upper limited temperature is 258.15 K), indicating that ForA might have an important role in MSA-driven NPF. The enhancing effect of ForA is mainly caused by an increased formation of the (MSA)2(MA)1 cluster, which is involved in the pathway of binary MSA-MA nucleation. Hence, our results indicate that OAs might be required to facilitate MSA-driven NPF in the atmosphere.