Why are nitrogen oxides produced by diesel engines a pollution concern?

Nitrogen oxides ($N{O}_x$) produced by diesel engines are a significant pollution concern due to their detrimental effects on both human health and the environment.

Health and Environmental Impacts

• Human Health: Nitrogen dioxide, a primary component of $N{O}_x$, is a pungent, irritating gas known to cause inflammation and irritation of the breathing passages. Exposure can lead to pulmonary edema, which is the accumulation of excessive fluid in the lungs.12
• Smog Formation: Nitrogen oxides play a critical role in the formation of photochemical smog, a reddish-brown haze common in urban areas created by sunlight-promoted reactions in the lower atmosphere.12
• Acid Rain: $N{O}_x$ reacts in the atmosphere to form nitric acid, which contributes to the formation of acid rain. Acid rain is known to damage foliage, buildings, and monuments, and it can alter the pH balance of waterways.12

These pollutants are formed in diesel engines when combustion temperatures are high enough to cause molecular nitrogen in the air to react with oxygen.1