This pilot case study characterized modern-day polyethylene film high tunnels and critically examined potential indoor farm worker exposures. We conducted indoor and outdoor sampling and analysis for carbon dioxide, and other environmental parameters including temperature and relative humidity, inside a high tunnel with a new single-layer Sunmaster® polyethylene plastic film on a rural organic farm in Maryland for a total of 12 weeks from early June 2017 to mid-July 2017 (summer season) and September 2017 to November 2017 (fall season). Concurrently, sampling of formaldehyde was performed June-July 2017 (data presented separately). Carbon dioxide levels indoors were measured above outdoor ambient levels with some samples near or exceeding indoor air quality guidelines, possibly due to poor ventilation and emissions from the polyethylene film. Sunny conditions led to higher indoor temperatures. Fall season indoor mean relative humidity was higher than outdoor relative humidity.