Nitrous acid (HONO) is important in the atmosphere because it produces OH radicals, which help clean the air. However, daytime HONO levels are often higher than expected, suggesting there are sources we don’t fully understand. This study explores whether certain organic nitrates (RONO₂), which form when air pollution reacts with sunlight, might help explain the extra HONO.

Researchers looked at how RONO₂ interacts with iron-containing surfaces like those found in dust and aerosols in the atmosphere. They found that both light and dark reactions with iron can break down RONO₂ and release nitrogen compounds like NO₂. This NO₂ can then form HONO and other reactive gases. A key part of this process is the iron itself: when Fe³⁺ is reduced to Fe²⁺, it drives these reactions, especially in low-oxygen conditions.

This shows that iron-based reactions are an overlooked way RONO₂ breaks down and helps explain extra HONO in the air. These findings suggest atmospheric models should include iron chemistry when trying to understand how pollutants are transformed and how reactive nitrogen (NO_y) cycles in the environment.