JAEA develops real-time, automatic measurement of airborne sea salt

The standard method for measuring airborne sea salt particles that drift inland from the ocean and contribute to corrosion in bridges and buildings involves spreading a piece of gauze, exposing it to the air for one month, and then collecting it to extract the salt content. While this "dry gauze method" is a standard approach registered under Japanese Industrial Standards (JIS), it remains limited by the significant time and labor required, as well as its poor time resolution.

A research group including Assistant Principal Researcher Kyohei Otani and Leader Takahiro Igarashi from the Research Group for Corrosion Resistant Materials at the Nuclear Science and Engineering Center of the Japan Atomic Energy Agency (JAEA), along with Shinyei Technology Co., Ltd. has successfully established the world's first method to measure airborne sea salt particles automatically and in real time using a commercially available pollen sensor. This approach not only dramatically reduces human labor but also captures short-term fluctuations that were previously impossible to detect. It is expected to improve the accuracy of corrosion prediction, build a sustainable monitoring framework, and facilitate nationwide observational collaboration.

Commercially available outdoor pollen sensors function by shining laser light onto particles and measuring the intensity of the scattered light along with the degree of polarization, thereby identifying the particles based on their characteristics. Focusing on this particle measurement technology, the research group investigated whether a pollen sensor could detect sea salt particles within air where mineral dust, pollen, and other substances coexist.

Through laboratory experiments and a year of real-world environmental observations in a coastal area, they discovered that sea salt particles can be extracted with high precision based on their nearly spherical characteristics and degree of polarization. In particular, under conditions optimized to extract fine particles with a high degree of polarization, the researchers confirmed a strong positive correlation (a correlation coefficient of 0.939) between the particle count obtained by the pollen sensor and the amount of airborne sea salt measured via the dry gauze method. This demonstrates that the particle count from a pollen sensor serves as an effective indicator of the concentration of airborne sea salt particles in a given space.

Otani said, "During the course of my studies in meteorology, an area of interest to me, I learned the mechanism of pollen measurement sensors. It was the trigger for starting this research. To be honest, I didn't want to do research relating to the conventional method. Moving forward, I want to collaborate with several companies to establish methods for long-term continuous observation and to enhance the sophistication of a nationwide airborne sea salt map."