Dissolved Organic Matter and Inorganic Chemical Constituents Characterized in Large Hailstones from South-Central Texas
Abstract
Hailstones grow as they cycle through the updraft region of a storm rising or falling through an ideal atmospheric zone where supercooled water droplets collect and freeze on the hailstone. Very few studies have investigated the chemical composition of hailstones and influencing factors. We hypothesize that hailstones record signatures of inorganic chemical constituents, dissolved organic matter, and microbes from the atmosphere during hailstone formation and growth. In this study, we perform a comprehensive characterization of 90 hailstones from 3 storms in 2020 and 2021, from Del Rio, Burkburnett and Uvalde in south Texas. After cleaning the surface with ultrapure water, hailstones were melted in a closed glass container to avoid contamination and meltwater was vacuum filtered through a 0.2μm glass fiber filter. Physical attributes such as geometry and mass were recorded prior to melting and after cleaning. Probes were used to measure pH and specific conductance, ion chromatography was used to determine cations and anions, carbon analyzer was used to determine the total organic carbon, total carbon, inorganic carbon and total nitrogen. Three-dimensional excitation emission matrix was used to characterize dissolved organic matter attained using absorbance and fluorescence spectroscopy. Hailstones ranged between 47 - 86 mm in diameter and a mass between 58 - 199 grams. The results revealed pH between 6.21 - 8.74, specific conductance between 4 and 110 µS/cm. Major anions were Cl- (1 - 8 mg/L) and sulfate (0.2 - 2.2 mg/L), with some samples having elevated NO3- (6 mg/L), and major cations as Na+ (1-12 mg/L) and Ca2+ (1-33 mg/L). These hailstones contained concentrations of dissolved organic carbon (2-16 mg/L) and total dissolved nitrogen (0-4.8 mg/L). Strong protein-like (tryptophan or tyrosine) fluorescence was indicated using excitation-emission matrix analysis indictive of dissolved organic matter (DOM) that is primarily of freshly produced microbial provenance. Molecular weight distribution of DOM, concentration of trace elements, geochemical modeling to understand saturation and speciation of inorganic ions, is ongoing. This study will improve our understanding about chemical characteristics of hailstones and the atmospheric conditions at formation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.B22E1491N