Indoor Air Quality depends on many factors. We are all concerned about removing contaminants from our indoor environment, but just as important is to have adequate ventilation.

If we live in an area with clean outdoor air, then opening windows and allowing natural ventilation is all that may be needed. Unfortunately few of us are so fortunate. In the modern world, in cities or suburbs, the outdoor air may not be so clean.


Furthermore, with the emphasis on saving energy, newer green buildings are frequently more airtight than older structures resulting in reduced exchanges between outdoor fresh air and indoor air. Airtight buildings result in increased concentration of indoor pollutants. Building Code standards for a healthy building in the USA require a ventilation rate of 15 cfm per person (equivalent to 7 liters/second per person). In the European Union the standard is .5 air turns/hour.

These standards are based on maintaining a safe level of CO2 in the indoor environment. Since all humans exhale CO2 at a predictable rate the amount of measured CO2 in the building is used as an indirect measure of human bio-effluent concentration and building occupancy. The standards of ventilation rates referenced above are equivalent approximately to a concentration of CO2 of 1000 ppm. This concentration is not considered harmful .Actually OSHA allows a concentration of 5000 ppm in industrial environments if a worker does not remain in that environment for more than 8 hours. However there has been research done in Europe that indicates that CO2 concentrations above 2000 ppm may have a detrimental effect on human performance of various mental tasks. In addition the higher concentrations have been considered a factor in the Sick Building Syndrome.

Forced ventilation can achieve these targets and the environment can be healthy provided that the Air Conditioning is equipped with HEPA in-duct filters that are properly and frequently maintained. Without these HEPA in-duct filters the achievable particulate air content will only be PM10 not the desired PM2.5.

We also have to consider the levels of outdoor CO2 in the air that is being introduced through ventilation. The air with the lowest CO2 level in the USA is in Hawaii at the top of the Mauna Loa volcano with a measured value of 366 ppm. But if you do not live on top of that volcano the average value in your area will be in the range of 375 to 450 ppm which is typical of urban areas.

To maintain the desired CO2 level indoors the ventilation rate must be adjusted accordingly.


Adequate ventilation is necessary, but not sufficient. Even if the amount of CO2 in our homes is maintained at a safe level we know that most indoor pollutants are created or formed indoors. Fine particles (smaller than 2.5µm and described by scientists as PM2.5 ) are the most harmful to human health .This category includes volatile organic compounds (VOC) such as benzene, toluene and formaldehyde from smoking, cooking, gas stoves, cleaning fluids, solvents, pesticides. We must reduce the presence of these pollutants in our homes.

Epidemiologic studies indicate that indoor pollution is correlated with morbidity caused by allergic diseases. A significant study was done in a test of 8 homes in Fresno, California. Air purifiers were installed in the living rooms and bedrooms of these homes. After the 12 week study the researchers concluded that air purifiers reduced indoor PM2.5 levels with significant improvements in nasal symptoms in children with allergic rhinitis, when compared to the control group of homes that did not have the air purifiers installed.

In another study,using data from the Exposures of Adult Urban Populations in Europe Study (EXPOLIS), researchers determined that when advanced filtration was used,a reduction in PM2.5 of  27% for residences of Helsinky,Finland, was achieved.


Although we may not know the specific health risks in our home environment,common sense dictates that we take action that is possible. Installing suitable air purifiers must be part of our plan of action.Improving indoor air quality in our homes is our individual responsibility.




What the Scientists tell us

There is considerable research in academia on ambient air quality. However, ambient refers to outdoor air. Most of the research consists of statistical analysis of hospital admissions for respiratory problems or mortality rates on days when there is extreme air pollution.

The statistical analysis consists of what scientists call meta-analyses (systematic reviews) of single-city time series studies. Basically an average of multiple studies.

The only indoor air studies are those that investigate the effects of indoor open fire cooking.These are important studies, mostly by the World Health Organization (WHO), but they only apply to underdeveloped countries where these practices are unfortunately still prevalent. They are not relevant to indoor conditions in the modern world.

Scientists are still divided on what standards should be imposed on ambient air. The U.S. Environmental Protection Agency (EPA) promulgated the National Ambient Air Quality Standards (NAAQS) designed to establish regulation of fine particulate pollution. But other scientists believe that these standards are too lax, with allowable pollution levels above the standards of the World Health Organization (WHO).

The science of clean air is not settled.

The statistical studies of ambient air have, however, one important conclusion. They tell us that the pollution effect on human health depends in part on the size of the particles in the air.

In this case size matters.

We can use this information when we address indoor pollution solutions.

But improving indoor air quality in our homes is our individual responsibility.

We cannot wait for solutions from the academic world. Continue reading “INDOOR AIR POLLUTION -WHAT ARE THE HEALTH RISKS”

Green Buildings and Indoor Air Quality – Energy Efficiency or Clean Air?

Building Construction Industry

The construction industry has made great strides in improving building construction.

New building codes and credits for Green Buildings have resulted in more energy efficient buildings and the use of recyclable materials for greater sustainability.

However these advances have not necessarily improved the indoor air quality (IAQ). Modern homes and offices are frequently more airtight than older structures resulting in reduced exchanges between outdoor fresh air and indoor air.

Furthermore, modern buildings make greater use of synthetic building materials that have introduced new contaminants such as volatile organic compounds (VOC), which arise from sources such as paints, varnishes, solvents and preservatives.

The combination of reduced ventilation and the increase in volatile compounds has the potential for a buildup of toxic substances in the home environment.

In the USA as in many other countries, no federal law specifically regulates IAQ, even though people typically spend more than 90% of their time indoors.

Pollutant levels are typically several times to several hundred times higher indoors than outdoors, and consequently indoor air typically accounts for over 90% of human exposure to pollutants.

Building Certification Programs

Green Building Certification programs have increased globally with over 145,000 green certification projects concluded as of 2016 and are forecast to grow by 37% by the end of 2018.The European Union Directive of Energy Performance of Buildings foresees that by the end of 2020 all new buildings should comply with the goal of nearly zero energy performance.[1]

The major Green Building Certification Programs include the Building Research Establishment Environmental Assessment Methodology (BREAM) in the United Kingdom and the Leadership in Energy and Environmental Design (LEED) in the USA. These programs are used in multiple countries around the world. Other significant programs are the Comprehensive Assessment System for Built Environment Efficiency (CASBEE) in Japan and recently (2016) the Deutsche Gesellschaft für nachhaltiges Bauen (DGNB) system in Germany. However there is no standard criteria that is used universally to define a Green Building. Different systems emphasize different Building characteristics.

But these projects, which give credits to builders for compliance, emphasize efficient use of resources (e.g., energy, water and materials) and sustainability.

But not much incentive is given for improving  Indoor Air Quality (IAQ).A recent study found that credits for IAQ accounted for only about 3 to 11% of the total credits.

This relative small percentage of credits for IAQ may be seen as inadequate incentive to pursue these credits.

Green Buildings and Health

Updates to the early Green Building Certification Systems now provide more weight to IAQ. Furthermore, other programs such as the WELL Building Standards [2] are focused specifically on IAQ. Typically Green Building Certifications have different requirements or Categories that need to be met in order to get the Certification. Some of the requirements address Pollution Source Control, Ventilation, and limits for specific pollutants such as formaldehyde, CO2, Volatile Organic Compounds (VOC) s. In addition they may require IAQ measurements. But the majority of requirements emphasize energy savings, water usage, building air tightness, minimize environmental disruption, and sustainability.

Many certificate programs allow “trading” of credits between categories. It may be possible to obtain Green Building Certification without complying with any IAQ requirements. One program, the German DGNB, is the exception in that it does not allow credit trading. Some compliance in each category must be achieved to get their Certification.

One problem that undermines improvements in the levels of IAQ in Green Buildings is that there is no consensus on what good IAQ is, or what factors affect the health of the occupants. Another problem is that some of the “green practices” used in the construction of Green Buildings have negative effects on the IAQ. In example using recycled materials may introduce in the building pollutants or toxic chemicals originated in the recycling process. Another example is the required use of green cleaning products for building maintenance. Many of the so called green cleaning products do not list all of their ingredients and may include fragrances. Fragrances are chemical additives that are dangerous pollutants that, when combined with ozone, can create secondary pollutants that have been proven to affect the health because of their microscopic particles that easily penetrate the respiratory system. In fact the US Centers for Disease Control and Prevention, Indoor Environmental Quality Policy states: “Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC”  [3]. Green Buildings have the potential to be beneficial to Health. However, we are not there yet. Progress is slow. It is up to us to control the pollution generated in our homes and to insure that we have adequate ventilation.[4]


It is my conclusion that we cannot rely on government programs to improve IAQ.

Improving indoor air quality of our homes is our individual responsibility.

Adding an Air Purifier can be part of our plan of action.

Click here to find out how you can check the air quality in your home.


[1] Anne Steinemann et al. Ten Questions concerning Green Buildings and indoor air quality.Building and Environment 112 (2017) 351-358

[2] WELL,The International Well Building Institute.The WELL Building Standard,V 1.0,Delos Living LLC,New York,, NY.,2015

[3] CDC,US Centers for Disease Control and Prevention. Indoor Environmental Quality Policy,2009,pp.9-10





About me

Hello, I am Carlos Gusts, a retired Industrial Engineer.

Now that I am retired I have the time to research and study the subject that is my passion.

How to achieve healthy indoor environments

I have seen first hand how indoor pollution affects people worldwide.Calling attention to what

improvements are  possible in this area can make a difference in people’s lives.I want to help.

Reporting on current research,and evaluating new products,is the mission of this website.

If I can be of any assistance please feel to contact me.

All the best,

Carlos Gusts

P.S. As a retired person I am also involved in research related to what makes retired persons thrive,not just survive. If you are interested you can visit my website on the subject