There are various techniques of purifying the air with the help of air purifiers. Mechanical filters, use of absorbents like charcoal, electrostatic charges or ionizers are some of them. The other setups that are required are germicidal UV light and the emission of ions into the air. These ions react with the contaminants and make them harmless enough to breathe.

Many asthma medications that asthmatics take are reactive since they are taken to relieve asthma attacks (generally caused by environmental triggers). Removing environmental triggers such as airborne allergens and contaminates will decrease asthma problems, enabling a reduction in medication.

There are several factors that a consumer looks for while selecting an air purifier. They are visual appeal, noise level and frequency of filter replacement. There are different types of air purifiers.

· Home Air Purifiers - Protect your home from airborne pollutants. It is Perfect for asthma, smoke, pet dander, mold, or other home pollutants.

· HEPA Air Purifiers - HEPA purifiers are time tested air purification solutions that offer one of the best filtration systems for removing airborne particulates and organics. HEPA filters are specially made high grade filters which enable it to captured 99.7% of contaminates and particles that are 0.03 microns and larger in size.

· Ionic Air Purifiers - Ionic purifiers filter out small particles such as dust, smoke or pollen, and pump many negative ions into the air to provide optimal clean air performance. Studies show that a room with high concentration of negative ions promotes health, helps with sleep, tension, exhaustion, depression, allergies, exhaustion and many other ailments.

· Commercial Air Purifiers - Commercial purifiers are geared towards larger square footage applications and high pollution zones. They work well for large enclosed areas.

· Ultraviolet Air Purifiers - UV light tends to break down organic compounds extremely well. Using ultraviolet light, these UV air purifiers sanitize bacteria in the air.

The CADR, or Clean Air Delivery Rating, is a standardized indicator of how well the air purifier can function as compared to the others. The higher it is, the stronger is the power of purification. They are rated by the Association of Home Appliance Manufacturers based on the stringent requirements as produced by the association.

• Reduces up to 99.4% of bacteria & germs
• New Permanent Lifetime True HEPA vacuumable filter
• QuietCare technology for ultra quiet operation
• 3 speeds with filter clean monitor
• Recommended for medium rooms

Product Description
True HEPA filter removes 99.97% of all airborne particlesfrom the air passing through the filter such as pollen, cat dander,household dust, tobacco some & mold sporesAmazon.com Review
This portable air cleaner is recommended for filtering the air in a closed room as large as 168 square feet (12 by 14 feet). As it continuously circulates a room's air--about six times per hour--it employs two filters to remove smoke, pollen, dust, animal dander, dust mites, molds, bacteria, viruses, and odors. Especially useful for asthmatics and allergy sufferers, the cleaner contains a true HEPA filter that is at least 99.97 percent effective at trapping extremely tiny particles (as small as 0.3 microns) while a prefilter reduces odors. Honeywell's IntelliCheck system permits monitoring the filters' lives. Each filter has a button. Pressing a button activates a light, which blinks or shines steadily. One blink indicates that the filter has lots of life remaining, two blinks means less life, three blinks means even less, and a steady light indicates the filter needs changing. The HEPA filter lasts one to three years; the prefilter, three months. Filter replacement is simple, and replacement filters can be ordered separately. The air cleaner has three speeds, and all are exceptionally quiet for an air cleaner this large and powerful. It carries a five-year warranty against defects. --Fred Brack

Honeywell 17000 Permanent Pure HEPA QuietCare Air Purifier

• Electric air purifier for large rooms; removes 99.97 percent of particles passing through
• Removes up to 99.4 percent of tiny particles like bacteria and germs
• Lifetime True HEPA filter vacuums clean for easy maintenance
• Patented 360-degree air intake and discharge for purifying large areas
• 3 speeds with filter-clean monitor; accepts #38002 charcoal and #24000 HEPA filters

Product Description
True HEPA filter removes 99.97% of all airborne particlesfrom the air passing through the filter such as pollen, cat dander,household dust, tobacco some & mold spores

Honeywell 50250 99.97% Pure HEPA Round Air Purifier