How do I iterate a model over multiple fields using ModelBuilder?

I have built a model to interpolate air pollution from 40 recording stations using IDW. The results are then exported to an average for census divisions.

I need to repeat this process hundreds of times for every month for 15 years for five different types of air pollution. I have all of the data by year as a new field in the recording stations file (see below).

How do I re-run the model for every field without manually changing them each time? The Iterate feature should work, but which one do I use and how do I link it?

Table:

Recording_Station 03jan 03feb 03mar 03apr 03may 03jun 03jul ....
1                  26.5 27.5  22.2  32.3  34.5  45.4  55.4
2                  19.1 12.2  45.3  33.3  36.6  55.4  65.5
3                  11.1 15.6  44.4  34.4  66.6  55.4  44.6

etc.