Plant-based release system of negative air ions and its application on particulate matter removal.

Particulate matter (PM, especially PM2.5 with diameter 2.5 microns) has been regarded as the major air pollutant. Negative air ions (NAIs) could electrically charge PM and remove it much more efficiently. In this study, a bio-generator of NAIs has been developed, which helps plants to generate NAIs at around 100 × 106 ions/cm3 under pulsed electrical field (PEF) treatment. By using the bio-generator, PM2.5 concentration in a growth chamber could be reduced from around 500 to near 0 µg/m3 within 5 minutes. It could also be used to remove continuously generated PM. Upon PEF treatment, genes encoding oxidoreductases and other enzymes were up-regulated, some of which might contribute to the generation of superoxide anions (one of NAIs). On the other hand, the emission of large numbers of electrons from the surface/edge of plant leaves has been detected upon PEF treatment and these electrons might be captured by surrounding air molecules to generate high concentration of NAIs.