Efficient Nitrate Formation in Fog Events Implicates Fog Interstitial Aerosols as Significant Drivers of Atmospheric Chemistry

Clouds and fogs, consisting of tiny water droplets formed by the condensation of water in supersaturated air, are vital in atmospheric chemistry, as they facilitate multiphase reactions. While measuring high-altitude cloud is challenging, fog as ground-level clouds offer a unique opportunity for direct observation. In this study, we explored radiation fogs in the North China Plain using an advanced aerosol-fog sampling system to measure the chemical and physical properties of both inactivated interstitial aerosols and activated fog droplet residues. Our findings revealed that efficient nitrate formation primarily occurred on fog interstitial aerosols rather than within fog droplets, with observed fog interstitial aerosol nitrate net production rates reaching up to 3.6 μg m