What are oxides of nitrogen, and how do they contribute to the formation of photochemical smog?

Oxides of nitrogen are gases formed when nitrogen and oxygen react at high temperatures, such as in vehicle engines. They contribute to photochemical smog by reacting with volatile organic compounds in the presence of sunlight, leading to the formation of ground-level ozone, which is a key component of smog.

A strong answer should directly address the approved learning objective to explain that oxides of nitrogen can contribute to photochemical smog. This question belongs to Properties and effects of atmospheric pollutants within Common atmospheric pollutants and their sources, so the response should use that exact curriculum context rather than a generic statement. The answer is correct when it names the key idea, explains the link to oxides of nitrogen, and keeps the wording specific to AQA GCSE revision.