The Hidden Reactivity of NO2: What Lab Studies Reveal

Nitrogen dioxide, or NO2, is a big player in the atmosphere's chemical game. It's a primary pollutant that sets off chain reactions leading to smog, acid rain, and tiny particles floating in the air. Scientists have been studying how NO2 behaves when it touches different surfaces, like dust, water droplets, or soot. These studies show that NO2 can change into other chemicals, like nitrates or nitrous oxide, through a process called heterogeneous chemistry. For example, on wet surfaces, NO2 can split into HONO and HNO3. On dust, it can turn into nitrates and NO, while on sea salt, it can produce nitrates and NOCl.Even light can change NO2 into nitrates or N2O5 on certain surfaces. All these reactions affect how much NO2 there is in the air and how it behaves. Scientists also found that SO2, another pollutant, can team up with NO2 to create even more reactions. The speed at which NO2 reacts on different surfaces, called uptake coefficients, varies and depends on factors like surface type and temperature. Despite all this knowledge, there's still much to learn about NO2's behavior in the atmosphere. Future research could help fill in these gaps.