This study investigated formaldehyde and acetaldehyde passive sampling rates and ozone interference for the DNPH-based Waters Sep-Pak XPoSure sampler. Previous studies have shown that ozone interferes with active sampling by this cartridge. Our study included one laboratory and six field experiments conducted in Northern California homes. Passive sampling rates of 1.10 ± 0.09 and 0.86 ± 0.10 mL/min determined for formaldehyde and acetaldehyde are lower than previously reported. In a controlled laboratory experiment there were small, statistically insignificant impacts of subsequent ozone exposure on formaldehyde and acetaldehyde mass passively collected on the samplers. This sampler is inexpensive, easy to deploy and to transport by mail, and has a high sampling capacity when used passively; it is suitable for a wide-range of monitoring applications. However, the passive sampling rate remains in question given the internally consistent, but different results obtained in our study and the previous study.