I-131 is the biggest contributor to dose for the population. This is Iodine-131, which has a short half-life of 8 days, so it decays quickly and will be mostly gone within a couple weeks or so.
For the area near the nuclear plants, there will be a few months of elevated radioactivity, and their biggest problem will be fission and decay products released from failed fuel bundles in the fuel pools which are open to the atmosphere. Xenon and Krypton are typical. However, it should not be a case where there is an extended period of elevated radiation levels or exposure to radioactive contamination (aka...fallout) which could be presented as either airborne or ground-based, or both.