Does bad air affect respiratory function in people with diseases like asthma or pulmonary fibrosis?

Yes. People with chronic respiratory diseases should avoid heavily polluted air. Air quality alerts are issued for areas when there is a high concentration of pollution. These are usually reported on the local weather reports. In some instances, poor air quality can even cause chronic lung disease. For more information on this, go to the american lung association website.
Yes. Pollution, dust, high pollen levels during allergy season can greatly affect and exacerbate diseases like asthma (from my experience in kids) and i would think that the same could be said for other pulmonary diseases like pulmonary fibrosis.

Related Questions

Asthma attack. Will peak flow reduce if the person has pulmonary fibrosis?

Usually. If there is reversible air flow blockage, that would show as a decrease in peak flow that reverses when the attack is cleared. The difference between a usual and reduced peak flow will be lower in pulmonary fibrosis since the volumes of air are decreased overall. Read more...