During thermal inversion, vertical mixing of air is suppressed, causing pollutants to accumulate near the ground.
Fine particulate matter (PM\(_{2.5}\) and PM\(_{10}\)) becomes trapped, leading to dense smog and poor visibility in urban areas.
Hence,
\[
\boxed{\text{Particulate matter}}
\]
is the correct answer.
Therefore,
\[
\boxed{(C)}
\]