Water-soluble ions in hailstones in northern and southwestern China

Interactions between aerosols and hydrometeors in deep convection remain largely unknown, which is at least in part due to the lack of direct observations. The natural hailstones grow when traveling in deep convection and could provide perspective of aerosols information in deep convective storms. Hailstones have been collected and examined with various techniques to measure representative atmospheric chemicals, which is a great help in defining their origin and structure as well as in understanding the microphysical mechanisms and aerosols-collection processes in deep convection.

In this study, hailstone samples were collected from 15 different hailstorm events across China, each of which occurred on a different date in 2016. The concentrations of 10 water-soluble ions, consisting of 4 inorganic cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺), 4 inorganic anions (Cl^-, NO^3-, SO₄^2-, and NO^2-), and 2 organic anions (HCOO^-and CH3COO^-), were determined in 15 hailstone samples. Inorganic cation concentrations in the melted hailstone samples ranged from 0.0 to 14.9 mg/L. Inorganic anion concentrations in the melted hailstone samples ranged from 0.0 to 16.4 mg/L. Organic anion concentrations in the melted hailstone samples ranged from 0.3 to 29.7 mg/L. However, in contrast to the concentrations of the ions in different hailstorm events, the concentrations of the ions of different hailstones in one hailstorm (Beijing, June 10, 2016) varied little. To determine the sources of the ions, we calculated the Pearson correlation coefficients between the concentrations of the 10 ions and 6 surface environmental pollutants, as well as the AOD by using these 15 hail events data. The presence of these ions suggests that hailstones are likely to scavenge ions along its growth route, based on the correlation of ion concentrations with AOD. PM10 was found to have the most significant positive correlation with all ions in hailstones (except NO₃^-), which suggests that most of these detected ions in hailstones are likely originated from PM10.

This was a preliminary study designed to provide evidence of the presence of water-soluble ions and the possible sources in natural hailstones and may shed light to future research in the interactions between aerosols and hydrometeors in deep convection.