Puy de Dôme Station (France): A Stoichiometric Approach to Compound Classification in Clouds

Abstract

Cloud droplets contain a complex mixture of water-soluble organic matter (WSOM) originating from the scavenging of soluble gases and the dissolution of cloud condensation nuclei (Ervens et al., 2015;Herrmann et al., 2015). During the cloud lifetime, aqueous-phase reactions lead to (photo-)oxidative transformations that potentially produce small organic compounds, such as diacids and dicarbonyls (

Emerging investigator series: aqueous photooxidation of live bacteria with hydroxyl radicals under cloud-like conditions: insights into the production and transformation of biological and organic matter originating from bioaerosols

“…, peptides and terpenoids), which could lead to the incorrect classification of peaks that fall within these overlaps. 72…”

“…71 To better understand how the composition of biological and organic compounds released from the four bacterial strains evolved during photooxidation, the O/C and H/C ratios of the identied WS and WIS compounds were visualized on VK diagrams, which is a commonly used tool to graphically visualize and classify compounds in cloud water. 50,72 The WS and WIS compounds were categorized into seven groups based on the region of the VK diagrams that they were in according to their combined O/C and H/C ratios. Using previously reported boundaries of regions in VK diagrams, we divided the VK diagrams into seven regions: lipids, peptides, terpenoids, polyketides, unsaturated hydrocarbons, aromatic structures, and highly oxygenated compounds (HOCs) (Table S2 †).…”

“…A weakness of our approach is the partial overlap of some of the categories (e.g., peptides and terpenoids), which could lead to the incorrect classication of peaks that fall within these overlaps. 72 Fig. 3 and S9 to S11 † show the VK diagrams for the four bacterial strains at time points T1 and T2 during photooxidation initiated by H 2 O 2 and NO 3 − photolysis.…”

How Well Do We Handle the Sample Preparation, FT-ICR Mass Spectrometry Analysis, and Data Treatment of Atmospheric Waters?

“…As reported in Section 3.1, in our previous works [18,26,29,49], we excluded the spectrum of the blank in the spectrum of the sample using the specific tool in Composer software. From the beginning, we preferred to exclude rather than subtract blank peaks, which may be tricky due to shifts in abundance and potential carryover from the sample to blanks if other samples are analyzed prior to a blank.…”

“…Historically, researchers began with targeted analytical methods to focus on specific classes of compounds, like short chain carboxylic acids, aldehydes, or more recently, amino acids [20][21][22][23][24][25]. Only recent developments in high resolution mass spectrometry have enabled the non-targeted analysis of the whole composition of cloud water WSOM [26][27][28][29][30].…”