When it rains I think the air quality improves so you breathe in a humid and clean air instead of a dry dirty air.
Not exactly, but near enough:
http://www.bbc.com/future/story/20120305-youll-catch-a-cold-...
http://fampra.oxfordjournals.org/content/22/6/608.short
>Conclusion. Acute chilling of the feet causes the onset of common cold symptoms in around 10% of subjects who are chilled. Further studies are needed to determine the relationship of symptom generation to any respiratory infection.