Decomposition of formaldehyde in strong ionization non-thermal plasma at atmospheric pressure

Atmospheric emissions of volatile organic compounds possess a major threat to the environment, and controlling them is a key task for air pollution prevention and control. This paper presents a comprehensive discussion on the degradation mechanism and pathways for the efficient removal of formaldehyde (HCHO) in a synthetic polluted air stream by strong ionization dielectric barrier discharge (DBD) plasma at atmospheric pressure. The effect of specific input energy, oxygen concentration, relative humidity (RH), gas residence time, and initial HCHO concentration was studied. Findings reveal that higher voltage caused an increase in discharge power, while the current density dropped from 180.53 to 55.10 mA and 71.06 to 51.99 mA when oxygen concentration and RH increased from 2.4 to 20.6% and 18.9 to 84.1%, respectively. The key degradation active species were O-center dot and (OH)-O-center dot generated from the electrical breakdown of oxygen molecules and water vapour. Also, the removal efficiency reached 95.12% for the lowest initial concentration of 100 ppm at ambient temperature. Destruction of HCHO molecules can be achieved via direct electron attack or indirect gas-phase radical reaction. The strong ionization DBD is a promising technology to remove low concentration formaldehyde from polluted air streams.