The Model 450 consists of a single-stage impactor to remove coarse particles greater than 2.5 or 1.0 µm, a set of porous metal plates to adsorb gases species such as SO2, NO2, NH3 for analysis while allowing the small aerosol particles less than 2.5 or 1.0 µm to pass through, and a final filter to collect the fine particles for analysis.

Different coating material can be applied to the porous stainless steel plates to absorb different gas phase species of interest. The coarse particles are discarded. The sampling head is constructed of PTFE to minimize the loss of gas phase species by diffusion. The sampler operates at 10 liters per minute. The system includes a small quiet pump and a seven-day solid state timer allowing up to 14 programmable starts and stops over the 7 day period.