New mass spectrometry techniques for studying physical chemistry of atmospheric heterogeneous processes

Abstract

Ambient particles and droplets have a significant effect on climate, visibility and human health. Once formed, they undergo continuous transformations through condensation and evaporation of water, uptake of low-volatility organic molecules and photochemical reactions involving various gaseous and condensed-phase species in the atmosphere. These transformations determine the physical and chemical properties of airborne particles, such as their ability to absorb and scatter solar radiation and nucleate cloud droplets. The complexity, heterogeneity and size of ambient particles make it challenging to understand the kinetics and mechanisms of their formation and chemical transformations. Mass spectrometry (MS) is a powerful analytical technique that enables detailed chemical characterisation of both small and large molecules in complex matrices. This capability makes MS a promising tool for studying chemical transformations of particles and droplets in the atmosphere. This review is focused on new and emerging experimental MS-based approaches for understanding the kinetics and mechanisms of such transformations. Some of the techniques discussed herein are best suited for ambient samples, while the others work best in laboratory applications. However, in combination, they provide a comprehensive arsenal of methods for characterisation of particles and droplets. In addition, we emphasise the role of fundamental physical chemistry studies in the development of new methods for chemical analysis of ambient particles and droplets.

A cautionary note on the effects of laboratory air contaminants on ambient ionization mass spectrometry measurements

“…Ambient ionization mass spectrometry techniques use ionization in open laboratory air to generate mass spectra of complex mixtures. Over 40 different types of ambient ionization techniques have been developed in the past decade . Some of these methods include atmospheric solids analysis probe (ASAP), direct analysis in real time (DART), desorption electrospray ionization (DESI) and extractive electrospray ionization (EESI) …”

Disintegration mechanisms of charged nanodroplets: novel systems for applying methods of activated processes

“…In the expansion of 1=rðsÞ we keep terms up to the first order term in dr and the zeroth order terms in the expansion of 1=r lþ1 ðsÞ. Evaluation of integral (12) for every spherical harmonic with l . 0 yields…”

“…[4][5][6][7][8][9][10][11][12] The droplets in question are composed of solvent and charge carriers that may be simple ions such as sodium, potassium, [13][14][15] macromolecular ions (protonated peptides, charged polyethylene glycol) [16][17][18][19][20] or complexes of macromolecules such as nucleic acids [21] or proteins. [22] The droplet lifetime is determined by rates of dynamic changes such as fission through shape fluctuations, chemical reactions within the droplet and disintegration through solvent evaporation and fragmentation events that involve charged species.…”

response to reviewer # 2

“…Recent advances in the development and application of mass spectrometry (MS) techniques for the analysis of OA particles have been documented in a number of reviews (Noziere et al, 2015;Laskin et al, 2012Laskin et al, , 2013 Published by Copernicus Publications on behalf of the European Geosciences Union. Pratt and Prather, 2012a, b).…”