[Tribune7]

What the gubmint says:

Modern jet aircraft are equipped with cabin air systems that control pressurization, airflow, air filtration, and temperature. Commercial jet aircraft fly at very high altitudes, and therefore, their cabin air systems must provide a safe, comfortable, and pressurized environment. Older model airplanes, such as the DC-9, the B-727, and half of the DC-10’s, provide 100% fresh air to the aircraft cabin. Newer models of jet aircraft, including the MD-80, DC-10, B-737, 747, 757, and A-300, 320 and 310, provide up to 50% re-circulated air. The recycled air system allows newer model aircraft to conserve fuel. The effectiveness of these filtration systems is often the focus of debate on cabin air quality.

[1rudeboy]

I'm physiologically-sensitive to that kind of stuff, having had terrible asmtha as a child. Three-quarters of the way into a 7-8 hour flight I'm ready to die. And the problem has become worse in the past ten years or so. I dread flying for this reason alone. I also wonder how many air-rage incidents are aggravated by this kind of stuff.