PAN animation
The above animation shows how PAN help transfer Nitrogen to upper layer.
In the morning, the oxidation of terpene would produce acetaldehyde near surface. The reaction of acetaldehyde with NO2 would procude PAN. Thus in the morning PAN is produced near surface. In the afternoon, surface PAN is well mixed in the PBL. Since upper layer has lower temperature, PAN in the upper layer is well preserved. So in such mechanism, PAN helped to transfer Nitrogen to upper layers, which could be transported to longer distance and afect the atmospheric chemistry in longer distance.