Understanding Nitrogen Oxides From Traffic
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Nitrogen oxides form whenever fuel burns at high temperature in the presence of air, which describes almost any internal combustion engine. Nitrogen and oxygen, both normally stable and inert in the atmosphere, react with each other under the intense heat and pressure inside an engine cylinder.
Once released in vehicle exhaust, these gases contribute to two separate problems: they react with sunlight and other compounds to form ground level ozone, and they can also combine with moisture to contribute to acid rain further downstream from where the vehicle was actually driven.
Because emissions concentrate along busy roads, nitrogen oxide levels tend to be highest near major intersections and during peak traffic periods, then decline with distance from the road. This localised pattern is why air quality can vary noticeably between a house on a quiet street and one facing a busy road. Traffic calming measures, buffer plantings and setting homes back from major roads are among the practical design choices that respond directly to this pattern.