'Stumbled upon this info looking for information on how negative ionization occurs in nature.  (ie water, oxygen etc).

"When two different materials rub against each other, static electricity is generated. An electron is moved from one (leaving a positive charge) to the other (making a negative charge). Different polarities will attract, as when synthetic fabric cling to your body.
In nature, half of the ions are formed by radioactivity, cosmic rays, ultraviolet rays, airflow friction, falling water and half are produced by plants where they stream off the leaves, most notably pine and asparagus ferns. Excessive positive ions are found in hot desert winds and before thunderstorms. Excessive negative ions are found in mountains, near oceans and waterfalls (shower) and after thunderstorms.
It is reported that positive ions create depressed moods (blood serotonin increase) while negative ions provide euphoria. As an-ions travel freely through your body on the path of highest conductivity, they will enter and leave your body through the acupuncture points, maybe stimulating them on their way. A theory is that an-ions increase the alkalinity in the body as water splits in H+ ions neutralized by an-ions and OH- ions that will ionize alkaline minerals. The surplus ions will leave your body, if they accumulate you will get an electric shock when they leave in a bunch, as experienced when touching a doorknob especially in an air duct heated room. (Air conditioning may produce a positive ion stream.) Ions and free radicals can not be stored in your body without altering the electrical potential, but before they leave they can change the body chemistry.
The high winds in the upper atmosphere and the earth's magnetic field generate very high voltage, so standing at sea level you would experience a voltage gradient of about 400V per meter, and in the mountains maybe up to 2000V per meter, when the gradient reaches 1000V per millimeter the air gets ionized and becomes a conductor. Lightening and the spark from an electric fence are examples of this.
This voltage will let an-ions travel through the body (higher conductivity) from feet to head. This and the alkaline spring water is claimed to be why people in mountains live longer and healthier. Inside an urban dwelling (or a car) the voltage gradient will be zero (Faradays cage), just as steel beam constructions will weaken the magnetic field inside them. Ionizers are generally used to bring the natural outside atmosphere into your home."

from - fhttp://www.ionhealing.com/aahealth.html

also

http://www.causeof.org/plants.htm

http://www.negativeionsinformation.org/ions_vitamins.html

The "taosist immortals" were always said to be dwelling and moving in the mountains..