What is the primary pollutant measured during emissions testing?

The primary pollutant measured during emissions testing is often a combination of Volatile Organic Compounds (VOCs) and nitrogen oxides (NOx). This is due to their significant role in the formation of ground-level ozone, which is a major component of smog.

During emissions testing, the focus is on pollutants that contribute to air quality degradation and public health issues. VOCs are organic chemicals that can evaporate and contribute to ozone formation. Nitrogen oxides are also crucial because they react in the atmosphere to produce ozone, particularly in the presence of sunlight.

Both of these pollutants are essential in evaluating the environmental impact of vehicle emissions, as they contribute to respiratory problems and other health conditions. Thus, emissions testing targets these pollutants to ensure compliance with air quality standards, making it clear why this particular choice is considered the primary measure during testing.