How do temperature and altitude affect emissions testing?

Temperature and altitude have a significant impact on the efficiency of an engine's combustion process and consequently its emissions output. As altitude increases, the atmospheric pressure decreases, which can lead to a lower density of oxygen available for combustion. This can result in incomplete combustion, as the engine may not receive enough oxygen to burn fuel efficiently, leading to increased emissions of hydrocarbons and carbon monoxide.

Similarly, temperature plays a crucial role in the chemical reactions within the engine. Higher temperatures usually increase combustion efficiency but can also lead to the formation of nitrogen oxides if adequate control measures are not in place. At lower temperatures, combustion can become less efficient, potentially increasing the emissions output.

Thus, understanding the interplay between temperature and altitude is essential for accurate emissions testing, as these factors can directly influence a vehicle’s emission levels and the effectiveness of the smog check process.