A clogged PCV valve can cause which of the following smog-related issues?

A clogged Positive Crankcase Ventilation (PCV) valve can lead to increased Carbon Monoxide (CO) and Hydrocarbons (HC) levels in the vehicle's emissions. The PCV system is crucial for maintaining optimal combustion conditions by recirculating gases that escape from the engine's combustion chamber back into the intake manifold. When the PCV valve becomes clogged, it disrupts this process, allowing crankcase gases to build up.

This buildup can cause incomplete combustion of fuel within the engine. Incomplete combustion leads to higher levels of CO, as this compound is a byproduct of burning fuel that does not convert completely due to insufficient oxygen or poor combustion conditions. Additionally, the higher concentration of unburned fuel can increase HC emissions, which result from fuel that is not fully burnt during the combustion process.

In summary, a clogged PCV valve hinders proper venting of crankcase gases, thus contributing to increased CO and HC emissions due to reduced efficiency in the combustion process.