What is Aeroponics and how does it differ from Hydroponics
In Aeroponic gardening the plants are watered and nourished by a mist instead of a flow or pool as is the case with standard hydroponic gardening. It is closely related to hydroponics but differs in many major respects. The plant roots and part of the stem are sprayed / misted with nutrient enriched water.
A grow medium is not used, the root systems instead are suspended by a support structure that minimizes contact with the plant. Optimally 100% of the plant should be exposed to the air so as to avoid hinderance of natural plant growth and root expansion and allow for access to pure water and air exchange.
A common issue in hydroponic gardening is oxygenation of the roots, this is not so much of an issue in aeroponics as the roots are persistently exposed to the air. Plants are nurtured to maturity with a plentiful blend of oxygen, water and nutrients. Oxygen  stimulates plant growth and helps prevent the formation of microbial disease / pathogens.
In addition to 02 [Oxygen] plants need C02 [Carbon Dioxide]. Carbon dioxide exists in nature at 300 to 400 ppm [Parts per Million] and is an essential element for plant propagation. In a closed system such as a greenhouse, CO2 content declines drastically during the day cycle due to photosynthesis when the plants inhale CO2. During the night cycle C02 will be replenished as the plants exhale or respire. Frequent ventilation of the greenhouse gases with outside air will help in regulating the CO2 cycle.
In order to track the C02 levels in your garden you will need take a measurement. A C02 monitoring system can be purchased online or at your local hydroponics supply center. C02 levels vary depending on the day / night cycle and other miscellaneous factors but as a rule of thumb it should be between 1,000 and 2,000 ppm. If your Co2 levels are low some C02 monitoring systems will automatically boost C02 levels if they fall below acceptable parameters.
If you have an extensive system and you feel it is economically worthwhile you might also want to invest in CO2 enrichment, such as a C02 generator or Boost bucket. C02 exhale bags are commonly used in greenhouses also, they are an inexpensive route to go and work well for smaller aeroponic / hydroponic scenarios and confined areas.
There are also several do it yourself methods for boosting C02 levels. See: Do it Yourself C02 generators
Mist Droplet Size and Nutrients
As stated at the initiation of this article, Aeroponically grown plants are nurtured by a mist instead of a flow or pool like standard hydroponics. This naturally involves different equipment. Misters, spayers, foggers and similar doohickies create a fine mist of nutrient solution for delivery to the plants roots. A true aeroponics / Fogponics system incorporates deep cycle timers, high pressure pumps and high pressure mist heads to atomize the nutrients into a soft fog / vaporised water to deliver nutrients and oxygen to plant roots.
Aeroponic systems are usually closed systems providing all the water, nutrients and gases needed to provide a sustainable and reliable air culture environment for the robust propagation of plants. A primary aspect of aeroponics in relation to plant root development is the size of the water droplet / the mist. If the mist is too fine the roots tend to develop very fine hairy roots and fail to develop affluent lateral roots which is essential to sustained growth. If the mist / droplets are too large less oxygen is made available to the roots and anerobic conditions sometimes develop. The mist should be in the goldilocks zone, ‘just right’. This sometimes involves what some would call excessive tweaking, but once you hit that goldilocks zone it is worthwhile.
Nutrients which are essentially minerals and salt flowing through the equipment tend to accumulate deposits of the these minerals and salts and therefore require periodic maintenance.
Aeroponically grown plants are more sensitive than either soil based or hydroponically grown plants. They require due diligence and constant attention to nutrient density ratios, pH, and assorted factors. Aeroponic gardens are not something advisable for new comers and are best attempted once you have a grasp on the basics of hydroponics at the very least.