The primary raw material used for activated carbon is any organic material with a high carbon content (coal, wood, peat, coconut shells). Granular activated carbon is most commonly produced by grinding the raw material, adding a suitable binder to give it hardness, re-compacting and crushing to the correct size. The carbon-based material is converted to activated carbon by thermal decomposition in a furnace using a controlled atmosphere and heat.

The resultant product has an incredibly large surface area per unit volume, and a network of submicroscopic pores where adsorption takes place. The walls of the pores provide the surface layer molecules essential for adsorption. Amazingly, one pound of carbon (a quart container) provides a surface area equivalent to six football fields.

How Does Activated Carbon Work?

Physical adsorption is the primary means by which activated carbon works to remove contaminants from water. Carbon’s highly porous nature provides a large surface area for contaminants (adsorbates) to collect. In simple terms, physical adsorption occurs because all molecules exert attractive forces, especially molecules at the surface of a solid (pore walls of carbon), and these surface molecules seek other molecules to adhere to. The large internal surface area of carbon has many attractive forces that work to attract other molecules. Thus, contaminants in water are adsorbed (or held) to the surface of carbon by surface attractive forces similar to gravitational forces. Adsorption from solution occurs as a result of differences in adsorbate concentration in the solution and in the carbon pores. The adsorbate migrates from the solution through the pore channels to reach the area where the strongest attractive forces are.

With this understanding of how the adsorption process works, we must then understand why it works, or why water contaminants become adsorbates.

Water contaminants adsorb because the attraction of the carbon surface for them is stronger than the attractive forces that keep them dissolved in solution. Those compounds that are more adsorbable onto activated carbon generally have a lower water solubility, are organic (made up of carbon atoms), have a higher molecular weight and a neutral or non-polar chemical nature. It should be pointed out that for water adsorbates to become physically adsorbed onto activated carbon, they must be both dissolved in water and smaller than the size of the carbon pore openings so that they can pass into the carbon pores and accumulate.

Besides physical adsorption, chemical reactions can occur on a carbon surface. One such reaction is chlorine removal from water involving the chemical reaction of chlorine with carbon to form chloride ions. This reaction is important to POU treatment because this conversion of chlorine to chloride is the basis for the removal of some common objectionable tastes and odors from drinking water.

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Air ionizers rely on the chemical properties of particles. An ion is just a particle that is charged, either negatively or positively. This commercial device, a tabletop or stand alone unit, creates negative ions using electricity. The ions flood the room and seek out positively charged particles, such as dust, dander, bacteria, pollen, mold, smoke, chemical vapors, and many other allergens. Once bonded (remember, opposites attract), the particles are too heavy to float around where they can easily be inhaled. As a result, the harmful airborne particles become larger pieces of dirt on the ground where they can be cleaned by normal means.

Most particles near the ground, are positively charged. Natural phenomenon, like lightening or waterfalls, generate negative ions and ozone. This is the “fresh” smell you might encounter in an electrical storm or white rapids. Ozone is a naturally occurring gas related to oxygen. Our buildings’ insulation interferes with atmospheric air circulation, so an air ionizer seeks to compensate for this disequilibrium.

Often outdoor pollutants get a lot of attention. We do not want car exhaust or factory emissions to cause health hazards. But indoor air pollution remains a serious problem. Dust and mold collects inside heating and air conditioning ducts. Higher humidity inside allows bacteria to thrive. An air ionizer addresses these home and office sources of pollution and odor. The ozone that is created when negative ions are generated, battles pollution by breaking it down into smaller, harmless components. Ozone makes it more difficult for germs to grow, and deodorizes as well.

Ionizers conserve power and run silently, unlike fan-driven air purifiers. Another advantage over other purifiers is that no parts need regular replacement, because there are no physical filters. Even though most air ionizers don’t have a motorized fan, the ionization creates a faint breeze that helps to distribute the ions throughout a room. Some are also outfitted with screens or prongs that catch the particles of dust as they fall to the ground.

In World War II the Atomic Energy Commission needed a filter to protect researches from radioactive dust particles that might present a health hazard to them. The HEPA filter was born. It traps particles as tiny as .3 microns with an efficiency rating of 99.97%.

To give you an idea of the size of a micron, it takes 25,400 microns to equal 1 inch (2.54 cm). Conversely, 4/100,000ths of an inch equals one micron. In metric terms, a single micron is 1 millionth of a meter.

A particle of 10 microns is invisible to the naked eye. Pollen ranges between 5-100 microns. Human hair between 70-100 microns.

The rating for a HEPA filter is based on capturing nearly all microns .3 in size, verses .1 or even .001 because .3 microns are the hardest size to trap and the optimal size for passing into the human respiratory system. Therefore the .3 micron efficiency rating sets the highest standard.

A HEPA filter is so efficient that for every 10,000 particles that enter the filter within its filtering range, only 3 particles will get through. Surprisingly, HEPA filters become even more efficient the longer they are in use.

For this reason HEPA filters are used in environments that rely on high clean-air standards. Surgical facilities, tuberculosis wards, NASA clean rooms, and laboratories are a few examples of environments that utilize HEPA filters. HEPA filters are particularly useful for allergy sufferers.

Many imitations of HEPA filters pervade the marketplace, usually called HEPA -type filters. They are less expensive than true HEPA filters, rated lower, and do an inferior job of filtering the air. If your health requires the specific benefits and efficiency of a HEPA filter, check the packaging to make sure the filter is rated at an efficiency of 99.97% for microns .3 in size. If it’s a true HEPA filter, it will have this rating clearly marked.

The Science of Ultraviolet (UV) Light

UV-A is the least harmful and most commonly found type of UV light, because it has the least energy. UV-A light is often called black light, and is used for its relative harmlessness and its ability to cause fluorescent materials to emit visible light - thus appearing to glow in the dark. Most phototherapy and tanning booths use UV-A lamps.

UV-B is typically the most destructive from of UV light, because it has enough energy to damage biologic tissues, yet not quite enough to be completely absorbed by the atmosphere. UV-B is known to cause skin cancer. Since most of the extraterrestrial UV-B light is blocked by the atmosphere, a small change in the ozone layer could dramatically increase the danger of skin cancer.

Short wavelength UV-C is almost completely absorbed in air within a few hundred meters. When UV-C photons collide with oxygen atoms, the energy exchange causes the formation of ozone. UV-C is almost never observed in nature, since it is absorbed so quickly. Germicidal UV-C lamps are often used to purify air and water, because of their ability to kill bacteria.

Simultaneously, Volatile Organic Compounds, including solvents, alcohols, dyes and fuel oils are broken down into basic elements, water and carbon dioxide. The titanium dioxide photocatalyst becomes highly reactive when exposed to precisely controlled wave lengths of ultraviolet light (medical grade UVC). When organic pollutants become present, the photocatalyst attacks the chemical bonds of the bioaerosol pollutants, therefore converting the toxic compounds into benign constituents.

Air cleaner strengths: Filters the air and collects dust, especially the larger dust (mostly dead skin) and pet dander.

Air cleaner cons:  Most air cleaners feature a fan that on high can make a lot of noise pollution. Expensive replacement filters, expensive to purchase. Most do not address the negative ion issue.

Air purifier strengths: Kills airborne pathogens that cause allergies and sickness. Many air purifiers offer silent operation. Less expensive to operate than air cleaners.

Air purifier weaknesses: Little or no dust removal capabilities. Without good air circulation, can only purify the air in a portion of one room. 

Air cleaners are often judged by a CADR (clean air delivery rate) number or by the number of air exchanges per hour.  CADR however only tests for larger particles (pollen, dust, over .3 micron in size) and not for viruses, mold, mildew, bacteria, VOC’s, chemicals, or cigarette smoke….in other words, they test for things that make us sneeze, not things that make us sick or even kill us. 

Air Purifiers on the other hand have a different mission. Their job is to purify or sanitize the air of things that cause odors or make us sick. Some use heat (Airfree), others UV or negative ions, yet others use ozone. Ozone generators are often sold as air purifiers which has the EPA’s panties in a wad, but for good reason.  Most are sold by MLM direct marketing to little old ladies who buy the sales pitch …”it’s like a rain forest in your home” they say. However, ozone, while it’s not a toxic gas or smog, it is a very strong oxidizer and harsh on the lungs in large quantities. A little bit of ozone, that’s fine, monther nature makes ozone in clean environments.  But in those clean environments there are not any nitrous oxides, a by product of ozone generators (in high concentrations) and there is not a lot of ozone.  Ozone generators are best used for shock treatments in empty rooms, that’s it. Don’t let anyone tell you otherwise.  What if you smoke? Well then I guess it’s better to breath ozone than second hand smoke. But that’s the exception to the rule. However, you’d be better served with UV technology. The Air Oasis Xtreme for instance can clean the air as well as an ozone generator without the  high ozone levels. The Ionic Zone PCO Sanitizer can also remove VOC’s and odors from the air.

How do UV air purifiers purify the air?  They utilizes hydrol radicals and super oxide ions or high intensity UV lamps (UVC induct units) to fry the DNA of microorganisms passing by. Often referred to as  “mother natures broom”, hydrol radicals are very short lived, but very effective at purifying the air. UV and photocatalytic oxidation is gaining ground as the weapon of choice in the war against indoor air pollution.  the old standard, negative ions (ionizers) on the other hand is losing ground mostly due to the negative press from the Ionic Breeze. However, the Ionic Breeze is not an ionizer as it produces a positive charge, not negative to attach particles to their negatively charged plates.  Regardless, negative ions are stil an important component of indoor air and worthy of your consideration.  

The best air purification devices in the world utilize air cleaning and air purifying technologies together to address a myriad of indoor air quality issues.  One of our favorites is the NQ Clarifier.  It utilizes 2 UV lamps along with 15 lbs of carbon and 80 sq ft feet of medical grade HEPA.  It runs on under 100 watts and has a dial speed control which allows for ultra silent operation.  We also love the Austin Air Allergy Machine and the Airpura I-600 for dust and general odor abatement.  While those units are air cleaners, they can also purify the air with carbon and UV germicidal lamps.

We hope this article helped you understand the difference between air cleaners and air purifiers and the different technologies available today. If you still have any questions, give us a call and we’ll be happy to assist you with the perfect solution to your particular indoor air quality concern.

As the market leader, it is our objective to contribute to the Indoor Air Quality industry by serving and educating consumers of the benefits of an improved environment.

We commit to contribute towards improving our customers’ environment with advance and high technology systems of the highest possible quality.

Our Customers shall be offered cost effective and practical solutions for their air quality applications.  We promise environmental solutions by working closely with selected manufacturers that offer quality and advanced systems, complete with efficient support. We shall be involved with all our partners – principals, suppliers, dealers and contractors, in various aspects of relationship marketing.  Together we shall strive to provide satisfaction to each customer.

AAQ specializes in the Design, Selection, Supply, Installation, Testing & Commissioning and after sales service.