Final answer:
An amber haze over a city typically indicates the presence of nitrogen dioxide (NO₂), which is a significant contributor to urban smog formation and acid rain.
Step-by-step explanation:
An amber haze over a city indicates the presence of nitrogen dioxide (NO₂). NO₂ is part of a group of gasses known as "nitrogen oxides" and is a prominent component of urban smog. The notable reaction 2 NO(g) + O₂(g) = 2 NO₂(g) is an essential factor in smog formation. NO₂'s reddish-brown color contributes to the visible haze and its presence correlates with various environmental and health concerns, such as acid rain and respiratory problems.
When NO₂ reacts with water vapor in the atmosphere, it can produce nitric acid (HNO₃), an essential component of acid rain. This acid rain can cross state and national boundaries, causing environmental issues far from the original emission source.