An Analysis of Salt Concentrations in the Rainwaters of Kāneʻohe, Hawai’i

Abstract

Sea spray aerosols (SSA) are a naturally occurring aerosol in marine regions, formed from white-capping and wave breaking along coastlines. SSA are hypothesized to play a significant role in the local climatology of coastal areas by acting as giant cloud condensation nuclei (GCCN), which can accelerate warm rain initiation due to their high hygroscopicity. However, there is large uncertainty about how much SSA mass makes it up into the clouds and participates in precipitation formation. SSA in the atmosphere are also collected by raindrops as they fall, further complicating the issue. To investigate the question of how much SSA is in rainwater, we analyzed the salt content of rainwater on Oʻahu at daily intervals from Kaneohe. We compared the salt content in rainfall to atmospheric variables to see how wind speed, wind direction, humidity, and rainfall play a role through their modulation of rain processes. We found that on average, Sodium and Chloride held a strong inverse relationship with total water mass. However, we found a weak relationship between ion concentration and rain rate with ion concentrations becoming inconsistent at lower rain rates and holding relatively low values with higher rain rates. The goal of this work is a more complete understanding of the concentration of salt in rainwater on Oʻahu and the changes from day to day due to atmospheric variability.