FAA seems like it has really let america down. The Max 8 thing and now they've sat on their hands for almost 2 decades after being ordered to assess the way pilots are being poisoned.
The FAA delegated safety to mfgs. (ODM), which in general doesn't work as well as expected. The actual 737 Max design problems were caused by Boeing, then false documents were filed with the FAA, so you could argue that beyond the ODM system, Boeing deliberately misled the FAA, subverting the safety certification process. The challenge with cockpit/cabin air quality is that fundamentally air flows from high pressure…
A first step to investigating how serious of an issue the air quality is during fume events would be to actually measure the air quality during fume events, which congress instructed/mandated the FAA do in 2003, per the article. But to paraphrase, the airlines told the FAA to take a hike, and they obeyed.
If the mfg can repeatedly mislead the regulators and the airlines they are purportedly regulating can tell them to pound sand when they try to investigate, it means the regulators are failing. Yes it also means Boeing is in the wrong and the airlines, but it means the FAA has dropped the ball.
I'm not sure what you're trying to say with the statement that gas flows along pressure gradients... temperature flows along temperature gradients... why does that standard behavior change anything in the analysis.