Nitrogen dioxide is a toxic gas that is hazardous to our health at as little as 20 ppm concentration, the equivalent of just 20 molecules in one million molecules of air. This gas is often found indoors from combustion and poor ventilation, so it is crucial to know if air purifiers can remove it.
Air purifiers with activated charcoal and/or titanium dioxide (TiO2) filters can remove nitrogen dioxide. However, purifiers that have ozone producing ionizers, UV-V (185 nm) bulbs, or ozone generators can add nitrogen dioxide to the room.
Nitrogen dioxide can cause irreversible pulmonary damage and even death. Therefore, it is crucial to ensure its removal from the house. In this article, we discuss which type of air purifier can help remove nitrogen dioxide and whether or not air purifiers can actually contribute to the problem.
What is nitrogen dioxide?
Nitrogen dioxide or NO2 is a highly reactive gas primarily created during combustion. When fuels burn at high temperatures, nitrogen and oxygen react to produce nitrogen monoxide (NO). When released into the air, it reacts with oxygen to form nitrogen dioxide.
This toxic gas is also emitted from welding, refining metals and gasoline, food manufacturing, nitric acid production, and soil microbes.
Sources of nitrogen dioxide at home
The primary sources of nitrogen dioxide in homes are stoves, heaters, boilers, and furnaces. To produce energy, they burn gas, coal, oil, kerosene, etc., and NO2 is formed in the process.
Apart from domestic appliances, exhaust from attached garages can also contribute to nitrogen dioxide concentration in homes.
Side effects of nitrogen dioxide
Nitrogen dioxide is a major air pollutant. Its harmful side effects include:
Difficulty Breathing
Being a toxic substance, NO2 irritates the throat, causing difficulty breathing. It reduces oxygen levels in the body which lead to headaches, nausea, wheezing, and coughing.
Irritation
Nitrogen dioxide exposure can cause a burning sensation in the eyes, skin, and throat.
Lung Damage
NO2 is mainly a lung irritant. When inhaled, it converts into nitric and nitrous acids in the distal respiratory tract. This damages the lung structure and impairs its function. The gas also generates free radicals that oxidize proteins and cause apoptotic cell death.
Exacerbation of Respiratory Disorders
The inflammation and damage to the lungs increase their sensitivity to environmental toxins, which worsens asthma and emphysema. This is further aggravated by a shortness of breath.
Ischemia
A study concluded that short-term exposure to nitrogen dioxide could result in ischemic heart disease (narrowing of heart arteries).
Mutations
A study revealed that ozone and nitrogen dioxide could together damage DNA and cause genetic mutations.
Safe levels of nitrogen dioxide
Currently, the EPA does not have a standard safe level for NO2 indoors. However, 0.053 parts per million (ppm) for 24 hours is considered a limit for outdoor air.
Health complications are known to occur after exposure to 20 ppm of the gas, while a concentration above 150 ppm for just 30 mins to an hour leads to rapid death.
Can air purifiers remove nitrogen dioxide?
Air purifiers are appliances that extract contaminants from the air. They draw air inside the system and pass it through a filtration system. Each filter removes a different type of pollutant. The clean air is then emitted into the room.
Whether or not an air purifier removes a substance depends on its filters.
Filters That Don’t Remove NO2
The filters in air purifiers that are ineffective against nitrogen dioxide are:
Pre-Filter
Almost all air purifiers have a pre-filter that improves the optimal life of other filters and protects the unit. It has large pores sized 100 to 3000 microns. Because of this, it only captures dust and debris and fails to capture tiny airborne contaminants such as NO2.
True HEPA Filter
A HEPA, or High-Efficiency Particulate Air filter, removes most microscopic pollutants. Its 0.3-micron pores can trap almost all particulate matter present in the air. Even germs like bacteria and mold spores that are bigger than 0.3 microns are removed from the air.
The term “True HEPA” is used for filters that conform to DoE filtration standards. Their efficiency is as high as 99.97% of particles as small as 0.3 microns. Almost all mainstream brands dealing in domestic air purifiers use True HEPA for effective filtration.
Unfortunately, HEPA filters fail to remove NO2 and VOCs because they are not particles and they simply pass through the filter pores.
Ionizer
Some air purifiers have an ionizer that produces static electricity inside the unit by generating negatifve ions. These ions attach to the airborne particles present in the air purifier and cause them to fall on and adhere to the surface.
Apart from the particulate matter, an ionizer may be effective against tobacco smoke, but it does not affect gases like NO2 and VOCs.
UV Bulb
Air purifiers employ UV sterilization inside the unit via UV bulbs. They emit light of ultraviolet wavelengths. Most of them emit UV-C (256 nm), which is one of the most effective disinfectants. It kills viruses, bacteria, mold spores, etc., and plays a crucial role in preventing many diseases.
Apart from germs, the bulb may also remove some gases like amine, carbon disulfide, styrene, etc. However, we don’t have substantial evidence of its effect on NO2.
Electrostatic Chamber
Electrostatic air purifiers have a chamber through which air is passed. Inside the chamber, positive and negative ions are produced that attach to pollutants, causing them to stick to the surface.
Like ionizers, they can only remove particulate matter.
Ozone Generators
Ozone is a gas comprising three oxygen atoms. It is unstable and readily decomposes to give up the third (nascent) oxygen atom. This oxygen atom changes the chemical makeup of surrounding substances, altering their chemical properties (and toxicity).
Artificially, they are produced by splitting oxygen atoms via electricity or ultraviolet radiation. This generates an oxygen atom, which combines with oxygen molecules to form ozone.
Since it works by changing the chemical composition, ozone removes gases and VOCs from the air. However, it does not work for NO2.
Filters That Do Remove NO2
Here are the filters that can remove NO2:
Activated Charcoal Filter
Activated charcoal (carbon) filters are manufactured by heating and oxidizing common charcoal. The process makes the substance highly porous. When air circulating in the air purifier encounters an activated charcoal filter, the gases it contains are adsorbed to the carbon surface.
After adsorption, the gas molecules, such as NO2 are trapped in the pores, which prevents them from escaping back into the air.
TiO2 Filter
Titanium dioxide or TiO2 is a photocatalytic substance often coated on filters in air purifiers. In the presence of light, TiO2 forms oxygen radicals that break down organic compounds, gases, and VOCs in the air.
TiO2 filters are particularly effective against nitrogen oxides and dioxides.
Can air purifiers add nitrogen dioxide to the room?
Apart from removing nitrogen dioxide from the air, air purifiers can, in fact, also contribute to its concentration in the room.
Ozone Creation
Although air purifiers remove toxic substances from air purifiers, they may also produce some harmful by-products during the process – one of which is ozone.
Ozone production is not just limited to ozone generators. Instead, ionizers and UV bulbs may also create and emit ozone.
Ozone and NO2 Production
We know that ozone changes the chemical composition of surrounding gases. While this effect helps reduce the toxicity of the original contaminant in some cases, it may also cause the formation of more dangerous substances.
One such example is the production of NO2. Air contains nitric oxide, which is unstable and readily reacts with ozone. This reaction oxidizes nitric oxide, forming nitrogen dioxide.
And it’s not just air that contains nitrogen oxide, ozone can also react with the nitric oxide in tobacco smoke to form nitrogen dioxide.
Ionizers and Ozone
Negative ions naturally occurring in the air are believed to be beneficial for overall health. However, when high-energy particles are produced artificially, they split oxygen molecules, creating ozone.
UV Bulbs and Ozone
UV bulbs used in most air purifiers produce UV-C light, which is germicidal. It is safe for the environment and does not result in dangerous by-products.
However, some bulbs may also produce different wavelengths of light, one of which is UV-V. UV-V has a shorter wavelength, i.e.185 nm. It breaks oxygen molecules into atomic oxygen that eventually forms ozone.
Best air purifiers for nitrogen dioxide removal
To remove NO2, you need an air purifier that:
- Has an activated charcoal filter or a TiO2 filter
- Does not produce ozone
Based on this criterion, here are six of the best air purifiers you can consider buying for NO2 removal:
PureZone 3-in1 Air Purifier
PureEnrichment is a renowned brand of appliances, and this device is their PureZone 3-in-1 True HEPA Air Purifier. It has three-stage filtration; a combined filter having a pre-filter and activated charcoal filter, a True HEPA filter, and UV-C light.
While the pre-filter, activated charcoal filter, and HEPA filter remove 99% of particulate contaminants, the UV-C light further enhances the filtration.
As per independent testing, the UV-C (emits 256 nm and doesn’t produce ozone) bulb installed in PureZone Air Purifiers eliminates 99% of viruses. It also kills bacteria like E. Coli (by 96.6%) and Staph albus (by 96.6%). The light also kills the most abundant mold, Aspergillus niger, by almost 88.2%. This plays a crucial role in preventing allergies and diseases.
This device comes with replacement filters and a 5-year warranty.
Alen BreatheSmart 45i
The extensive coverage of 800 sq. ft., versatile controls, and elaborate filtration process makes Alen BreatheSmart 45i an excellent air purifier for NO2 removal.
It has a pre-filter, a Medical Grade 13 True HEPA Filter, an activated charcoal filter, and a B4-Pure Filter.
Just like pre-filter and HEPA filters, the B4-Pure filter also removes particulate contaminants like dust, allergens, pollen, pet fur, and dander.
While the activated charcoal filter removes NO2, it also makes sure you have a fresh-smelling indoor environment.
hOmeLabs Air Purifier
The hOmeLabs Air Purifier has a three-tier filtration system made of a pre-filter, a True HEPA filter, and an activated charcoal filter. The Medical Grade 13 HEPA and activated charcoal filter together remove 99.97% of the smallest particles in the air. On low to medium fan speed, these filters can provide 24/7 operation for up to 2100 hours.
Vremi Premium True HEPA Air Purifier
Vremi Premium True HEPA Air Purifier comes with three-stage filtration that includes a pre-filter, a True HEPA filter, and an activated charcoal filter.
One of the best parts about its pre-filter is that it has ultrafine pores. This implies that it can capture relatively smaller particles than other generic pre-filters. The HEPA filter further aids in the effective removal of airborne particles, whereas the charcoal filter is essential for odor (and NO2) reduction.
The HEPA filter and the activated charcoal filter do not need to be rinsed or cleaned, making the system easier to maintain.
LEVOIT Core 300 Air Purifier
LEVOIT appliances have a large customer base in America. For NO2 filtration, their LEVOIT Core 300 Air Purifier is the one to look for.
It comes with a True HEPA and an activated charcoal filter. Once switched on, this system can significantly improve air quality in almost 12 minutes. This high-speed premium filtration is achieved by the Vortexair Technology and 360 degrees rotation feature. It cover up to 219 sq. ft. area, making it a good fit for small to mid-sized rooms.
Dyson Pure Cool Link Air Purifier
Dyson Pure Cool Link TP02 is a smart air purifier compatible with Wifi and Alexa. One of the coolest features of this appliance is that in summers, it can act as a makeshift fan.
It comes with a HEPA filter that removes up to 99.97% of particles and germs that measure 0.3 microns or more. The second filter is an activated carbon filter that captures odorous gases and VOCs like paint fumes.
One of the key features of the purifier is that you get real-time air quality updates via the Dyson Link App, allowing you to control the air purifier via your smartphone remotely.
FAQ
Should you run air purifiers 24/7 for nitrogen dioxide?
The rising pollution makes us prone to hazardous airborne contaminants like germs, dust, debris, and harmful gases. High-quality air purifiers can filter these pollutants with more than 99% efficiency, providing crucial protection against them.
Nitrogen dioxide is primarily caused by appliances like stoves and furnaces typically used for long hours. In case of poor ventilation, this can significantly increase NO2 in the room, leaving you at risk of severe health complications.
It is ideal to run an air purifier 24/7 if you have a nitrogen dioxide problem as it can help remove it from the air.
What happens if you inhale nitrogen dioxide?
Inhaling low concentrations (few ppm) of nitrogen dioxide causes difficulty breathing, cough, and throat irritation. In contrast, long-term exposure of hours to days can manifest as pulmonary edema, bronchospasm, and airway obstruction. Breathing over 200 ppm of the gas can immediately prove fatal.
What does nitrogen dioxide smell like?
Nitrogen dioxide has a pungent, acrid, bleach-like smell. The odor can be detected at 0.1 ppm or 188 µg/m3.
How do you test for nitrogen dioxide?
Apart from its odor and health side effects, nitrogen dioxide at home can be tested and identified using a nitrogen gas detector (Amazon link).
What are the symptoms of nitrogen dioxide?
Symptoms of acute exposure to nitrogen dioxide are coughing, fatigue, headache, and difficulty breathing. The emission of gas can also be identified by its characteristic pungent smell.
How long does nitrogen dioxide stay in the atmosphere?
According to the EPA, nitrogen dioxide has a high global warming potential (273 times that of carbon dioxide) and stays in the atmosphere for 114 years.
As nitrogen dioxide takes a long time to decompose, it is crucial to reduce its emission to the environment. Some of the measures that can help the cause are
- Limiting Use of Nitrogen Fertilizers: Nitric acid is a critical component of fertilizers, and its production generates nitrogen dioxide as a by-product.
- Installing SNCR or SCR: Selective non-catalytic reduction (SNCR), selective catalytic reduction (SCR), or their hybrid models are cost-effective air pollution control equipment that limits nitrogen dioxide emission from industrial plants.
- Reduced Motorized Vehicles: Combustion in motor engines creates nitrogen dioxide, which is released into the environment via the exhaust.
