How do temperature and humidity affect vehicle emissions?

Temperature and humidity significantly influence vehicle emissions primarily by affecting combustion efficiency and the formation of pollutants. In warmer temperatures, the air is less dense, which can lead to a different air-fuel mixture during combustion. This alteration can affect how completely fuel burns, potentially resulting in higher levels of unburned hydrocarbons and other pollutants being emitted.

Humidity plays a similar role; when humidity is high, the increased moisture content in the air can influence the combustion process. Water vapor in the air can affect the engine's performance and efficiency, potentially leading to an increase in emissions. Moreover, certain pollutants, such as ozone, are also affected by temperature and humidity levels in the atmosphere, which can influence their formation during the combustion process or through photochemical reactions.

Therefore, understanding how these environmental factors interact with vehicle emissions is crucial for accurate emissions testing and for developing effective strategies to mitigate pollution.