A HEPA filter (High Efficiency on Particles Air) can filter up to 99.97% of 0.3μ aerial particles.
These filters are used to clean the air and retain suspended particles (dust, pollen, bacteria etc.) and other particles that can cause respiratory allergy in sensitive subjects.
All of them. Air because in helps make food it also lets the plant breath. Water because it helps move nutrients into the plant. Soil because plants can’t grow without soil.
