Which pollutant has the second smallest mean emission value?

Which pollutant has the second smallest mean emission value?

• A. CO2
• B. Part
• C. HC
• D. NOX

Answer: (C)

The idea is to compare the average emission levels of each pollutant and identify which one sits second from the bottom when you rank them from smallest to largest. In this data, the mean emission for particulate matter is the smallest, and the mean for hydrocarbons is the next smallest. That makes hydrocarbons the second-lowest by average emission. The usual pattern behind this ranking is that CO2 tends to be the largest emitter because it comes from all carbon-based fuels, NOX can also be high due to high-temperature reactions, and particulate matter is often reduced by filtering and clean-engine technologies, leaving hydrocarbons higher than particulates but lower than CO2 and NOX in this dataset.

The idea is to compare the average emission levels of each pollutant and identify which one sits second from the bottom when you rank them from smallest to largest. In this data, the mean emission for particulate matter is the smallest, and the mean for hydrocarbons is the next smallest. That makes hydrocarbons the second-lowest by average emission. The usual pattern behind this ranking is that CO2 tends to be the largest emitter because it comes from all carbon-based fuels, NOX can also be high due to high-temperature reactions, and particulate matter is often reduced by filtering and clean-engine technologies, leaving hydrocarbons higher than particulates but lower than CO2 and NOX in this dataset.