An inexpensive, potentially mobile field exposure system is described which may be easily constructed by a small workshop. It may be operated as an open-top with a frustrum or covered with a polycarbonate ‘lid’. The system is cost-effective for CO2 exposure work because the small size allows provision of CO2-enriched atmospheres over prolonged periods at relatively low cost. A preliminary assessment of the chambers has been made and concentrations can be maintained at ±6% for a target atmosphere of 680 cm3 m−3 CO2 under normal operating conditions. Other chamber environmental conditions are reported.