Tag Archives for " activated carbon "

Knock out the NOx

This title may sound like an ad for high-octane gasoline, but I’m talking about air pollution here!  In air purification “PM” or particulate matter often steals the show and drives the decisions behind purchasing this filter versus that filter and this purifier over that one.  But what about the gasses in air pollution?  Gasses are not particulates–they are harmful molecules in the air that cannot be filtered out by plain HEPA filters.  So what are they and how can we get rid of them?

NOx is one term for two nitrogen gasses commonly found in urban areas.  It includes nitric oxide (NO), which is a colorless, odorless gas, and nitrogen dioxide (NO2), which is a reddish-brown gas with a pungent odor.  They are produced during combustion: in factories, in transportation vehicles, and even boilers for heating apartments, office buildings, hospitals, universities, etc.  They’re also produced indoors by gas stoves and furnaces when they are not properly vented. 

Nitric oxide in ambient conditions is not harmful, as it dilates (relaxes) blood vessels and improves oxygenation.  However in higher concentrations, it does two things: it will create a burning sensation in your throat and chest as it changes into nitric and nitrous acid, and it goes deep into your lungs to react with blood cells and eventually be excreted by the kidneys.   Nitric oxide in the air that is not breathed in is converted to NO2, the other dangerous nitrogen gas, or precipitated in moisture as acid rain.  (Poison Facts: Low Chemicals: Nitric Oxide)  

According to Clarity.io, a manufacturer of air monitoring sensors, nitrogen dioxide pollution stays mostly concentrated in the area where it is emitted, meaning that areas with high vehicle traffic like urban areas tend to have the highest NO2 levels. (Clean air cities: Innovative approaches to improving air quality in urban settings)  NO2 is a pretty nasty gas: it causes inflammation of the respiratory pathways, worsened cough and wheezing, reduced lung function, increased asthma attacks and is likely to be a cause of asthma in children. (Nitrogen Dioxide)  

If you’ve been reading our articles or have any experience with air pollution or wildfire smoke, you’ll know that outside pollution eventually makes it into our homes, because they’re leaky.  Thus, we don’t have a “safe place” to get away from air pollution unless we leave the city or take steps to make our home air cleaner.  As we already discussed, just buying a plain HEPA filter or making a DIY air filter (Corsi-Rosenthal box) will not take NOx out of your home.  There are ways to get rid of NOx, however: upgrade to a HEPA filter with activated carbon, AND eliminate the sources of NOx inside your home.

A 2014 study conducted in Baltimore, MD found that a two-pronged approach really helped reduce the NO2 in homes:  

1. Replacement of unvented gas stoves with electric stoves reduced NO2 concentrations by 51% and 42% in the kitchen and bedroom, respectively, indicating that stove replacement impacts NO2 concentrations beyond the kitchen (even when the home also has a gas furnace or drier).

2. Placement of air purifiers with HEPA and carbon filters in the home results in a nearly 27% decrease in median kitchen NO2 concentrations immediately (1 week after placement), and reductions were maintained at 3 months following intervention. 

Although the study also included the addition of a ventilation hood in some homes, it was unclear whether the hood helped lower NO2 emissions (ventilation does help remove air pollution, but it depends on strict use of the hood during and after cooking).  

Activated carbon adsorbs the NO2 and secures it in the filter, until the filter is changed.  Adsorption of NO2 can be enhanced by 38-55% by adding coatings to the activated carbon, such as potassium hydroxide (KOH).  (Development of an activated carbon filter to remove NO2 and HONO in indoor air)  Even wildfire smoke has NO2 in it; according to this Canadian government environmental webpage, wildfire smoke is a complex mixture of gases, particles and water vapour that contains pollutants such as: sulphur dioxide, nitrogen dioxide, carbon monoxide, volatile organic compounds, fine particulate matter (PM2.5), and ozone.  Activated carbon can handle these gasses and VOCs, while HEPA filtration is used against PM2.5

Therefore, city dwellers, take note!  Whether it’s “business as usual” as pollution from downtown traffic penetrates your home, or wildfires hundreds of miles away turn the skies orange and hazy, a purifier with HEPA and activated carbon is your best bet to knock out the NOx.  Be on the lookout for purifier giveaways, too!   Here are some programs being offered at this time:

• San Joaquin Valley Air Pollution Control District (California) is giving away air purifiers to keep residents safe from air pollution.  If you live in the area, you can apply for one here. 

• The City of Philadelphia is giving air purifiers to early-childhood education centers and schools.  You can learn more and link to an interest form in this article.

• Project N95, a national non-profit working to protect people and their communities during the COVID-19 pandemic and beyond, has begun a donation pilot program of air purifiers for schools and other organizations.  You can fill out their form here.

Keep your eyes and browser open, as other organizations may spontaneously donate during events like the Canadian wildfires (the University of Connecticut gave away 100 DIY purifiers on June 8, 2023).  During such a time, it’s the neighborly thing to do!

To-Do List: Change the Cabin Air Filter in your car and ADD CARBON!

I know, car maintenance is not everyone’s “thing” and air filters sound super-boring.  However, if you’ve owned your car for a while and never changed the filter, or bought a used car and have no clue when this filter was last changed, you could be horrified at what you would find (and hence are breathing in every time you drive it)!  It’s time to think of this task as a “health upgrade” for you, the driver or passenger!

Cabin air filters in cars (tip: these are different from the engine air filter) are probably even more neglected than household air conditioning or furnace filters, for several reasons:  our car ventilation systems are exposed to even more dust, toxins and critter debris than our homes, and many people are averse or afraid of car maintenance.   However, it’s so easy to order the right filter online with your car’s model and year, and now virtually every maintenance procedure on every model car can now be found on YouTube.  There’s no excuse for rolling up your sleeves and getting to it (or bribing your teenager or neighbor to do it with some food)!   Simple tools like screwdrivers, sockets and a vacuum cleaner are usually the only things needed. 

Before you order the filter, however, check to see if they are available with activated carbon.  If so, definitely get that one.  Not only does carbon help with smells in your vent system and car interior, it can remove NO2 from ventilation air.  Nitrogen Dioxide (NO2) is a by-product of fuel combustion and it irritates our respiratory system, causing flare-ups of asthma, which can trigger a visit to the emergency room if the coughing and difficulty of breathing is not controlled.  Over time, NO2 can actually cause asthma or respiratory infections.  A study in the UK at the University of Birmingham showed how much the activated carbon lowered NO2 levels compared to basic pollen filters.  In heavy traffic, many people close the windows and put the ventilation system on “recirculation mode”, which helps reduce NO2 levels by about 1.6 times compared to open windows.  However, you shouldn’t keep the windows closed and recirc on for extended periods of time because CO2 levels will start to rise; maintaining appropriate ventilation is also important to prevent drowsiness.  Here’s the alternative:  using external ventilation with activated carbon filters fitted.  Even with fresh air coming through the ventilation system, NO2 levels were 6.6 times lower than levels with windows open.  Also, in-vehicle NO2 levels were on average 14.3 times lower with closed windows and recirculated air.  It just makes sense to go with activated carbon if it’s available in a filter for your car. 

With minimal research and $, you can feel a lot better about the air you breathe on every drive.  Then, you can place a reminder on your calendar to do it again next year, and keep up the good habits!

What’s in a chemical filter?

Current events certainly stimulate a lot of research, and the accidental release of toxic chemicals from storage and transportation units is no exception.  When a dangerous chemical is odorless and colorless, how can we possibly protect ourselves and the air in our homes?  Enter chemical filters, which are actually already available for purchase.

Many gas filtration media start with a base material and then add (impregnate) the base material with specialized materials.  Since all of these base materials have a multitude of miniature holes that can get “plugged up” with dust, it’s best to make sure the dust filter is clean and in place to preserve the life of the chemical filter.  The base material is incredibly light because of the vast amount of internal surface area it has in its many cavities and holes.  The way these materials  purify air is called “adsorption” (in contrast to absorption).  Adsorption and absorption both “suck up” liquids or contaminants, but there is a difference:  a sponge will absorb water, but eventually the water leaks out or evaporates.  Activated carbon, activated alumina and zeolites adsorb certain chemicals, some including water, but the adsorbed liquid or gas does not escape because a chemical bond is made, until the material is regenerated with high heat.  Since adsorption is a surface phenomenon, good adsorbents are those having large surface areas per unit mass and high attractive forces for the compounds to be adsorbed, called the solute. Although all molecules are adsorbed to a certain extent, those having high polarity are likely to be more strongly adsorbed than those having low polarity. Since water is a highly polar material, it is much more strongly adsorbed than hydrocarbons, for instance. (Air and Gas Drying with Activated Alumina)

Here are the most common base materials:

A main ingredient in these filters is activated carbon.  We’ve written about it here but when you have something more dangerous than sweaty socks or cat litter smells, we like to dig a bit deeper on its capabilities and limitations.  Activated carbon removes volatile organic compounds (VOCs) and acid gasses, which make them useful against a wide variety of pollutants.  To review, VOCs are compounds that have a high vapor pressure and low water solubility.  They are natural and human-made chemicals that are used and produced in the manufacture of paints, pharmaceuticals, and refrigerants. (EPA.gov)  An acid gas is any gaseous compound which, when dissolved in water, will form an acidic solution.  Many industrial compounds are acid gasses, but did you know that we actually exhale an acid gas?  Carbon dioxide (CO2) is an acid gas, and activated carbon is a method for removing excess CO2 in a space.  

Activated alumina is another base.  It’s a porous, solid form of aluminum oxide, otherwise known as Al2O3 or alumina. This is the same mineral that makes up the precious gems ruby and sapphire, with impurities being the source of the stones’ bright colors. After activated alumina has been evacuated of existing moisture by heating it, the high surface area and many pores of the material allow for the uptake of water and other molecules through adsorption.  (What is Activated Alumina?) At about 1.5 to 3 times the cost of activated carbon, activated alumina is pricier but very attractive for adsorbing different chemicals.

Zeolites are another base material for chemical adsorbents.  They can be naturally occurring or man-made.  Zeolite has an aluminosilicate framework. Which simply means minerals composed of aluminum, silicon, and oxygen, plus countercations. This framework provides exceptional strength and stability to the honeycomb structure. It also makes it very difficult for the positively charged atoms (cations) to leach from Zeolite. (What is Zeolite?)   Molecular sieves are a type of zeolite that are manufactured to precise frameworks and pore sizes for specific applications.

Now that you know some of the base materials, additives (also called “doping”) can enhance capture/filtration of specific contaminants.  

• Potassium Permanganate is added when sulfurous compounds may be present (such as hydrogen sulfide and sulfur dioxide).   According to this filter company, their molecular sieve impregnated with potassium permanganate oxidizes gaseous pollutants such as hydrogen sulfide, sulfur dioxide, formaldehyde, ethylene, mercaptans, and various aldehydes and alcohols.   Do you know what mercaptans are?  They are the sulfurous, rotten-egg smelling additives that are added to natural gas to help you know that there is a leak.

• Potassium Iodide:  some AustinAir filters are impregnated with potassium iodide, for increased removal of formaldehyde and ammonia.  They are best used in places like new homes, laboratories, beauty salons, funeral homes, etc. Sources of formaldehyde in homes can be carpets, wood panel, construction materials and furniture upholstery, if not an outright chemical leak. (achooallergy.com)

• Magnesium Dioxide and Copper Oxide: The air filter company Blueair adds these compounds in their activated carbon filters to remove carbon monoxide, ethylene oxide, and ozone.

So which filter is best for me?  It’s hard to plan for every scenario, but you may take into consideration the following:

• This article/table by the California Air Resource Board (CARB) in response to the Aliso Canyon gas leak (California, 2015) describes what types of filters are in a number of high-end air purifiers.  The models may have changed slightly but it can give you an idea of how air purifiers can be used to reduce specific chemicals (mercaptans were judged to be the source of most peoples’ health issues).

• If you live very close to a refinery or manufacturer of specific chemical products, you may want to find out what chemicals they manufacture, store and load, what VOCs/fumes are produced and what air filter is best to remove those VOCs. 

• If you are interested in a particular type of filter, look for (or ask for) test data that verifies it removes what it’s designed to remove.  In an MIT study of 4 consumer-grade air cleaners, only 2 of them removed the VOCs toluene and limonene effectively.  

• In the case of radon, activated carbon filters (and the others mentioned above) will not adsorb radon gas, but they will adsorb most of the radon decay products (termed “radon daughters or progeny”), which are actually the source of health issues associated with radon. (Reduction of Radon Working Level by a Room Air Cleaner).   Therefore, activated carbon is not recommended for first-line defense against radon infiltration into your home; a venting system is more appropriate and you should contact a professional if you have radon in your home.

• In the end, activated carbon is widely used for a reason: it removes a lot of VOCs!  If you don’t have a specific chemical that you’re concerned about, this type of filter is a readily available, broad spectrum weapon against many pollutants.  If your air is particularly dusty, you’ll want to make sure that it also has a HEPA pre-filter to protect the activated carbon from getting clogged with dust.