Recently, after a flight I developed a cold and sore throat. Onee of my friends remarked that I often catch cold after a flight, particularly during winter.
Here is my theory: In winter when it is cold, pilots recirculate more inside air and bring-in less fresh air. In other words, more germs are recirculated.
My questions:
a) Does outside temperature dictate (guided by economics) how much fresh air is mixed in the cabin?
b) I assume that some kind of filters are used when air is recirculated. Are they capable of filtering cold viruses?
c) How often these filters are changed?