Classification of clouds sampled at the puy de Dôme (France) based on 10 yr of monitoring of their physicochemical properties

Abstract

Abstract. Long-term monitoring of the chemical composition of clouds (73 cloud events representing 199 individual samples) sampled at the puy de Dôme (pdD) station (France) was performed between 2001 and 2011. Physicochemical parameters, as well as the concentrations of the major organic and inorganic constituents, were measured and analyzed by multicomponent statistical analysis. Along with the corresponding back-trajectory plots, this allowed for distinguishing four different categories of air masses reaching the summit of the pdD: polluted, continental, marine and highly marine. The statistical analysis led to the determination of criteria (concentrations of inorganic compounds, pH) that differentiate each category of air masses. Highly marine clouds exhibited high concentrations of Na+ and Cl−; the marine category presented lower concentration of ions but more elevated pH. Finally, the two remaining clusters were classified as "continental" and "polluted"; these clusters had the second-highest and highest levels of NH4+, NO3−, and SO24−, respectively. This unique data set of cloud chemical composition is then discussed as a function of this classification. Total organic carbon (TOC) is significantly higher in polluted air masses than in the other categories, which suggests additional anthropogenic sources. Concentrations of carboxylic acids and carbonyls represent around 10% of the organic matter in all categories of air masses and are studied for their relative importance. Iron concentrations are significantly higher for polluted air masses and iron is mainly present in its oxidation state (+II) in all categories of air masses. Finally, H2O2 concentrations are much more varied in marine and highly marine clouds than in polluted clouds, which are characterized by the lowest average concentration of H2O2. This data set provides concentration ranges of main inorganic and organic compounds for modeling purposes on multiphase cloud chemistry.

Trace Metals in Cloud Water Sampled at the Puy De Dôme Station

“…The data matrix is automatically standardized by the software and the Pearson correlation coefficient is used. The number of factorial axes retained for the analysis is of two for each case presented: this limits the robustness of the PCA analysis, but it allows a better visual representation and comparison to the data presented in the previous classification by Deguillaume et al [31]. The combined plot of scores (coordinates of the samples on the new variables) and loadings (weights of original variables on Dimension 1 and Dimension 2) called bi-plot allows us to identify groups of samples with similar behavior and the existing correlation among the original variables.…”

“…Those samples are representative of the conditions encountered at the puy de Dôme, which, most of the time, are marine (52%) and continental (26%). More precisely, those samples represent a significant fraction of the clouds reaching the top of the puy de Dôme Mountain [31], where clouds result from air masses, coming from the west, north/west sectors (72% of occurrence).…”

“…Back-trajectory sectors of air masses reaching the puy de Dôme. Yellow lines depict the four different sectors identified: Air mass origin was calculated by NOAA-HYSPLIT using 72 h back-trajectory and the direction of air mass before arriving at the puy de Dôme mountain is reported in blue for marine samples and in red for continental samples, following the HCA1 (hierarchic cluster analysis) analysis performed on samples analyzed in this work plus samples from Deguillaume et al [31] (174 observations).…”

“…The combined plot of scores (coordinates of the samples on the new variables) and loadings (weights of original variables on Dimension 1 and Dimension 2) called bi-plot allows us to identify groups of samples with similar behavior and the existing correlation among the original variables. PCA is performed considering the concentrations in micromolar (µM) in order to classify cloud samples using the same approach of Deguillaume et al [31] (6 variables) ( Figure S1). For samples presenting concentrations below the detection limit, concentration values were considered equal to 0 in the statistical analysis.…”

“…The concentrations of 18 elements were analyzed by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Clouds are classified based upon the main anions and cations concentrations using principal components analysis (PCA) following the work from Deguillaume et al [31]. Here, trace metal concentrations are added to this statistical analysis with the objective to better discriminate cloud samples among continental and marine origins.…”