Valencia - industrial or traffic pollution spots?

It looks like we are honing in on Valencia to live. However the European Air Quality website shows the occasional amber flag for pollution in the area. This morning there were several, now there are two remaining so I guess it fluctuates. At Quart de Poblet and Moli de Sol. Does anyone know anything about these areas as to why they are flagged? Eg there might be factories or heavy traffic areas. Also what other places are known for pollution for whatever reason?

I'm not being picky, this is for serious health reasons. Thanks!