Spore trap sampling requires both a cassette and a calibrated vacuum pump, and is typically performed indoors to evaluate mold levels in occupied spaces. However, taking an outdoor sample is a critical part of interpreting your results accurately—and it’s often overlooked in DIY testing.

Indoor air always contains some amount of mold, and many spores found indoors come from the outdoor environment. Without an outdoor control sample for comparison, it’s difficult to know whether your indoor levels are elevated or completely normal for your area.

Outdoor sampling provides a baseline, allowing you to compare:

• Indoor vs. outdoor total spore counts
• Differences in mold types present indoors vs. outside
• Whether certain molds are likely coming from an indoor source

To collect an outdoor sample:

1. Set up your spore trap just outside the home—ideally in a shaded area, out of direct wind and away from plants or leaf piles.
2. Run the pump for the same amount of time and at the same airflow as the indoor sample (usually 5 or 10 minutes at 15 liters per minute).
3. Label clearly as “Outdoor Control – [Location/Time].”
4. Ship this sample with your indoor cassettes to the lab.

Helpful tip: Always take the outdoor sample on the same day and as close in time as possible to your indoor samples. If you’re only able to take one outdoor sample, do it at the beginning or middle of your indoor testing series.