Chemical composition of fogwater collected at four sites in North- and Mount-Lebanon during 2021

Abstract

A field campaign is established at four sites in North-Lebanon (Akkar district) and Mount-Lebanon (Keserwan district) for the first time between February and June 2021 using the Caltech Active Strand Cloud Collector (CASCC). Overall, 14 fog events are sampled, of which 5 samples from Fnaideq, 5 samples from Beit Younes, 1 sample from Qamouaa, and 4 samples from Bzomar. Their mean liquid water content (LWC) varies between 0.023 and 0.045 g m−3, their mean conductivity (K) varies between 53.3 and 2210 μS cm−1, and their pH varies between 6.5 and 7.8. The dissolved organic carbon (DOC) varies between 7.4 and 82.6 ppm. DOC shows a good correlation with magnesium and chloride, and no relationship with the liquid water content (LWC). The total average ionic concentrations (TIC) in Fnaideq, Qamouaa, Beit Younes, and Bzomar are respectively 3106.9, 4112.2, 4972.4, and 5969.1 μEq L−1. TIC shows a negative correlation with LWC (r2 = 0.7), suggesting that an increase in the LWC with dilute the solute concentration. The fog water in Lebanon is characterized by high concentrations of Ca2+ (35% of the measured TIC), Na+ (20%), Cl− (12%), NH4+ (11%), and Mg2+ (11%). The contribution of the acidic ions (SO42− and NO3−) from industrial and vehicular sources is minimum (respectively of 3% and 1%). NH4+, originating from the scavenging of gaseous ammonia and particulate ammonium nitrate and sulfate and from agricultural activities, and Ca2+‏, originating from the scavenging of coarse particles, act as acid neutralizers and are the main cause for the relatively basic pH of fogs in Lebanon. The contribution of Ca2+ and Mg2+ to sea-salt is found to be negligible, whereas the contribution of SO42− to sea salt is higher. Zn and Ni are the most two abundant heavy metals at all sampling sites. Their concentrations vary respectively between 137.6 and 349.7 μg L−1 (mean of 211.8 μg L−1) and between 38.2 and 585.5 μg L−1 (mean of 197.6 μg L−1). They account together for an average of 58% of the total elemental concentration. The high enrichment factors (higher than 100) for Ni, Cu, Zn, Hg, and Cd suggest significant anthropogenic contamination at the sampling sites. The ionic sources are also determined by the Principal Component Analysis (PCA). Two principal components (PCs) that account together for 62% of the total variance are identified by PCA. High ionic loadings are observed indicating a well-mixed mixture of local anthropogenic sources (factories, motor vehicle emissions, sea transportation, agriculture, combustion, civil construction, etc.) and some natural sources (sea and crust/soil).