Reactions of formic acid with protonated water clusters: Implications of cluster growth in the atmosphere

Abstract

[1] Obtaining direct and detailed chemical information about the initial stages of nucleation continues to be a challenging task, but it is necessary for improved understanding of the growth process of particles in the atmosphere. To elucidate the role of organic molecules, specifically formic acid, in nucleation and particle growth, the present work uses a flow tube reactor to study formic acid-water interactions using water cluster distributions of 2-30 water molecules. The reactions studied herein are compared to methanol-water interactions to provide evidence of a change to the stable clathrate-like structure of the H + (H 2 O) 21 "magic" cluster. Intensity ratios of the form] are used to identify prominent clusters in spectra containing pure water, methanol-water mixed clusters, and formic acid-water mixed clusters. Relative concentration flow rates of 12.5, 25, 50, and 125.5 standard cubic centimeters per minute (sccm) of formic acid were added to a pure water distribution, and the resultant spectra were compared to those from methanol relative concentrations of 25, 50, and 100 sccm. The formic acid-water mixed cluster distributions observed in these reactions do not contain a prominent peak in the intensity ratio graphs, indicating a disruption in the clathrate structure of the 21-molecule cluster while a prominent peak for 21-molecule cluster is observed in the methanol system. Also observed was an increase in intensity with increased cluster size, which indicates that formic acid-water mixed clusters could serve as a prenucleation embryo for the nucleation of water molecules and a possible particle growth pathway.

Evolution of aqSOA from the Air–Liquid Interfacial Photochemistry of Glyoxal and Hydroxyl Radicals

“…Different types of cluster ions (i.e., m / z + 165 (C 2 H 3 O 4 ···C 2 H 2 O 4 ) + , m / z + 367 (C 9 H 13 O 12 ···3H 2 O) + , m / z + 369 (C 9 H 15 O 12 ···4H 2 O) + and m / z – 635 (C 18 H 21 O 20 ···C 2 H 4 O 2 ···H 2 O) − ) are also observed, especially in the longer UV aging time. Our measurements support the hypothesis that water in the aqueous phase plays an important role in oligomer and cluster ion formation due to proton transfer and surface proton reaction …”

Photoionization, Structures, and Energetics of Na‐Doped Formic Acid–Water Clusters

“…Then, was postulated hydrated FA clusters could grow more easily than pure water clusters [6] . FA clusters are mainly studied using mass spectrometric methods detecting protonated species mainly resulting from fragmentation processes [7–9] . Information on neutral acid‐water cluster mass distribution may be obtained, in some cases, with alkali metal doping methods and UV photoionization.…”

UV Photoionization of Sodium‐Doped Formic Acid Clusters

“…[1] These organic compounds are a subject of concern because they can alter the properties of atmospheric particles, especially due to their hygroscopic properties [2] that impact the aerosol growth. [6] Clusters are finite-size systems that, depending on their dimensions, share the properties of molecules and bulk systems. [4,5] Accurate investigations of these topics cannot disregard the molecular details involved in aerosol formation and growth.…”