Why Indoor Air Quality Matters
Research has shown that air quality and COVID-19 together with other viruses and communicable diseases are correlated. A big point of concern when talking about IAQ is that indoor air is usually 2 to 5 times more polluted than outdoor air and most persons spend the majority of their time indoors. An adult person breathes about 22,000 times a day consuming more than 30 pounds of air molecules per day.
Various factors affect indoor air quality, which are affected by the indoor space and a person’s habits, and it is important to take these into consideration.
Key IAQ Factors - Ideal Ranges
Group A: Factors affecting Virus Transmission
Temperature- 66 to 75 F:
According to research by Casanova Lisa, et al., published in the American Society of Microbiology, the infectious rate of viruses is significantly reduced at moderate room temperatures compared to colder temperatures < 39 F. At warmer temperatures > 86 F, transmission of the virus is blocked or becomes highly inefficient.
Relative Humidity- 40 – 60%:
In an environment with RH% lower than 40%, droplets from a cough or sneeze lose their moisture quickly resulting in droplets becoming “dry aerosols” and capable of staying in the air for longer time periods creating a viral cloud that remains infectious for much loner time periods. Virus particles are most inactive at 50% humidity and retain their infectiveness the further from that median average, plateauing at 20% and 80%. 50% RH is the most ideal in terms of fast virus inactivation.
PM 2.5 – 15 ug/m3 (micrograms per cubic meter):
Particle Matter also known as “particle pollution” is a complex mixture of extremely small particles and liquid droplets. PM at 2.5 microns in size or smaller will be inhaled deeply into the lungs and can cause irritation and corrosion of the alveolar wall which impairs lung function. They are also known to carry microbiomes, a microbe that stay alive and protects us against germs and diseases, as well as aids in digestion of foods.
A study conducted by Feng, Cindy et al published in the Journal of Environmental Health showed an increase in vulnerability to influenza-type illnesses when levels of PM2.5 were above the ideal range. The study suggests that these PM2.5 stay airborne longer, creating a “condensation nuclei” which virus droplets attach to. This becomes part of the viral cloud that gets inhaled by people increasing the risk of infection.
Common sources of PM2.5 are smoking, candles, cooking, space heaters, furnaces, poorly maintained HVAC systems and poorly ventilated fireplaces.
Carbon Dioxide Co2- < 800 ppm:
Co2 has long been used as an indicator of good indoor air quality primarily because of its association with ventilation. When Carbon dioxide levels are high, it may indicate that your spaces are not well ventilated or there is an untypical source present for the production of this gas.
Chronic inflammation caused by persistent high Co2 levels is not ideal for our health, moreover longer exposure to high Co2 can cause fatigue, headaches, and dizziness. It is also possible to develop hypercapnia acidosis, characterized by increased levels of carbon dioxide in the blood that will suppress the human immune system and make on more susceptible to disease. Some typical causes of Co2 indoors are heavy population of people, improperly ventilated spaces, improperly maintained combustion devices and exposure to high output of car and diesel fuel burning exhaust.
Nitrogen Dioxide- NO2- below 53 ppb:
High levels of Nitrogen Dioxide indoors is a result of outdoor NO2 entering your indoor air environment as well as combustion sources inside the space. A study by the Environmental Research Journal, short -term exposure can irritate airways while long-term exposure can lead to chronic illness and respiratory infections with viruses. Asthmatics may also experience longer symptomatic periods and increased need for medication for children. Examples of sources of NO2 are automobiles from an attached garage and busy urban streets, appliance with defective installations, gas stoves, kerosene heaters, chimneys etc.
Total Volatile Organic Compounds (TVOC)- OSHA PEL of .75ppm and an action level of 0.5 ppm. Levels between 0.3 to 0.5 mg/m3 are considered acceptable:
According to the US EPA VOCs are emitted gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. They can also react with
Other chemicals in the air and become more dangerous to human health. Exposure to VOCS over a 24-hour period can irritate the lungs causing nausea and making it difficult to breath. Long term exposure to harmful VOCs over months can affect the liver, kidneys, and central nervous system.
Group B: Infectious Disease Promoting Factors
Airborne Mold Spores- No set standard. Guidelines are less than outside, no pathogenic species and total spore levels typically <1000 spores per cubic meter with no predominance of pathogenic mold types:
Not all persons are susceptible to mold spores at the same exposure levels. However even allergenic mold types can cause hay fever and asthma reactions as well as sinusitis, pneumonia and endocarditis. Pathogenic Species promote disease in humans even if they are in good health attacking their immune system.
Airborne Bioaerosols (mold and bacteria) – no overall quantitative exposure standards, but based primarily upon exposure to the mycotoxins and endotoxins present in pathogenic species:
Bioaerosols are very small airborne particles ranging from 0.001 to 100 um (micrometer) that originate biologically from plants and animals and can contain living organisms. Therefore, pathogenic and/or non-pathogenic dead and alive microorganisms may exist in bioaerosols. Mycotoxins are toxic compounds that are naturally produced by some mold types. Endotoxins are present inside some gram-negative bacterial cells that can be the cause of some infectious diseases. Bioaerosols are easily shifted from one environment to another because of their small and light weight. In recent years, exposure to bioaerosols in both occupational and residential environment has drawn much attention in light of their likely impact on human health.
How IAQ Affects Mortality Rates
Long before COVID-19 arrived, air pollution and poor indoor air quality have been linked to higher rates of illness and mortality. SARS Coronavirus research has found evidence that the virus is frequently spread in the air. Ke Lan an expert virologist from Wuhan University hypothesized that these tiny airborne droplets could cause coronavirus infections. Scientists from the Department of Community and family medicine in Hong Kong found evidence supporting this also. According to Harvard University, the same trend holds true. Their study looked at the data from years 2000 to 2016 and found that long term exposure to airborne particulate matter results in an increase in COVID-19 death rates, based upon their updated data of April 24,2020 suggesting that even an increase of 1 ug/m3 of 2.5 PM can increase the likelihood of mortality by 11%.
RH% (Relative Humidity) tells us how much water vapor is in the air, compared to how much it could hold at that temperature. It is expressed as a percentage. For example, 50% RH means the air is holding one half the water vapor it can hold, again dependent on temperature.
Rules of Thumb
As temperatures increase, the air expands and becomes drier, RH% decreases. As temperatures decrease, air becomes denser and wetter, RH% will increase. When thinking about air pressure, as air pressure decreases, air becomes drier and RH% increases. As air pressure increases, air again becomes wetter and RH% increases.
Comfort, Health and Safety
The most widely designated range for best human comfort is between 35 to 55%. This range will support the human immune system and not dry out eyes, noses and throats. Inside dew points are not usually reached and cool surfaces will not form condensation at typical temperatures. Levels below 30% cause irritation to eyes, dry out skin and will shrink mucous membranes reducing a person’s resistance toward upper respiratory illnesses. Lower levels down to 15% or less over time will cause DVT (deep vein thrombosis). RH% over 60% will support fungal growth on first condensing surfaces.
Impact on efficacy of UV (ultraviolet) 254 nm emissions, UVC PCO (Ultraviolet Photocatalytic Oxidation) and UVGI (Ultraviolet Germicidal Irradiation)
Past research performed to measure the effect of temperature and RH% on PRRS (airborne porcine and reproductive syndrome) virus showed that PRRS virus was more susceptible to Ultraviolet as temperatures decreased, most susceptible to UVC inactivation at RH% between 25 to 79%, less susceptible at < 24% and least susceptible at > 80%.
Another Study performed on three pathogenic airborne bacteria which entailed passing bioaerosols horizontally into a UV device, showed that increased UV resistance with relative humidity is likely associated with the hygroscopicity and increased aerodynamic diameters at high RH%. UVGI effectiveness was significantly increased with decreasing RH%.
Research published by 2020 UHOO in Singapore reported that virus particles are most inactive at 50% RH. Real time testing performed by AIAQS on Active and Passive technology combining UVC, BPI and activated oxygen showed that the combined efficacy was diminished as much as 20% at RH% exceeding 70%.