I have 8 porcelain crowns on top teeth and I have sensitivity to air. What can be done?

It could be that you have had
some gum recession and the cold air is causing the sensitivity on the roots of
the teeth that are normally covered by the gums. This does not
necessarily mean there is a cavity or decay, just exposed surfaces of the
roots. This can often times be resolved with a surface varnish or protectant
over the roots or even a desensitizing toothpaste like Sensodyne. In
extreme gum recession cases, a gum specialist (periodontist) may need to be
involved and they can actually recover the root surfaces with more gum tissue.There is always a possibility
that what you are experiencing is a micro gap that has formed between the
veneer and the tooth but typically this would be the case if only one or a few
of the veneers are sensitive, not all of them. Best advice would be to go
in and see the dentist that placed the veneers to evaluate.

If they are recently placed consider giving them time to adjust to treatment, have your dentist consider de-sensitizing the margins or using a desensitizing toothpaste.  If this has been going on for a while consider having xrays taken and your dentist try to isolate which tooth or teeth are sensitive.  Are margins open?  Is there any indication of nerve problems?  Are you sensitive to just cold or hot as well?  These are concerns you dentist must investigate. He/she may advise any of the above and give it a reasonable amount of time before more aggressive therapy that may include root canal therapy or even re-make of the sensitive crowned tooth.

To answer this question is a bit difficult without actually seeing the crowns. It's possible that there has been some recession displaying root structure which can be temperature sensitive. If you breathe thru your mouth when exercising the colder air may just be irritating those exposed areas.Other than that without examination there really is no better answer.