What are common procedures for lab absorption spectroscopy of gases? I'm doing research for applications of absorption spectroscopy. I'm trying to find common practices such as how the gasses are mixed, measured, contained, and discarded.

The gases involved will be those commonly found in the atmosphere or the human body. Top among these will be $\ce{NO2}$, $\ce{CO2}$, and $\ce{CO}$.
Non-dispersive infrared absorption spectroscopy is commonly used to measure $\ce{CO}$ and $\ce{CO2}$ (and other gases, like methane and $\ce{NO2}$). The absorption overlap from water interferes with $\ce{CO2}$ measurements in particular but various algorithms can be used to mitigate this.  

$\ce{NO2}$ is more commonly measured by chemiluminescence because of its high sensitivity, but FTIR and other techniques are used for higher levels (i.e. exhaust pipe and stack emissions).