Tiny particles in the air called ice-nucleating particles (INP) play an important role in how clouds form ice, which affects rain and snowfall. In the western Himalayas, we do not fully understand where these particles come from or how they change over time. To study this, we collected daily air samples over several months in 2022 and 2023. We then tested these samples in the lab to find out how many INP they contained and how easily they caused water to freeze.

We found that the number of INP increases as the temperature drops. There are more particles in the air during May and June. These increases are linked to dust storms and forest fires that bring different types of particles. Smoke from fires causes ice to form in clouds at warmer temperatures because it contains organic and biological materials. Dust particles cause ice formation mostly at colder temperatures because of their mineral content.

By tracking where the air came from, we saw that both forest fire smoke and dust travel long distances to reach the Himalayas. Our results also showed that 2023 had much higher INP compared to 2022, likely due to changes in weather and pollution sources.