The science correlating clean air with health issues is still evolving. There is no standard definition of “Clean Air”. As a result, most standards for building indoor air quality (IAQ) are established based on people’s perception of air quality. In this article we will examine both perceived air quality and actual clean air. We will present our conclusion and recommendations for achieving the healthiest indoor air possible.
Perceived Air Quality (PAQ), as the name indicates, is the subjective assessment of air quality by those living in a home or working in a business environment. Home builders want to build homes that meet the wishes of the occupants. To determine what standards must be achieved to that end the builders conduct field studies in which sample subjects are exposed to different environment conditions, and their satisfaction with that environment is recorded.
A typical study  varied three levels of air temperature and humidity and two levels of ventilation rate. The values for temperature and relative humidity were:
20 Degrees C/ 40% RH, 23 Degrees C/ 50% RH,26 Degrees C/ 60%RH
Ventilation in these tests was set as:
10 liters/ second per person
3.5 liters/ second per person
Other studies  have examined the effect of CO2 on air perception quality.
WHAT THE STUDIES SHOW
These studies show that there is not a single value for the parameters studied that would assure an acceptable perceived air quality. The studies only show that air is perceived as acceptable when it is cool and dry and unacceptable when it is warm and humid. The ideal conditions depend on your geographical location and time of the year. Ideal Humidity is between 30% RH and 50% RH. For example Canadian standards recommend 35% RH in winter and 50% RH in summer
Other recommended values are CO2 less than 1000 ppm and ventilation rate above 0.5 air change rate per hour( or 14 liters/sec per person).
Other factors are also considered for improving comfort. For example a Danish labeling system for building primary emissions of volatile organic compounds (VOC)  focuses on comfort by minimizing annoying odors and mucous membrane irritation. The values of the VOCs should be below levels that can be sensed by the occupants. These levels have nothing to do with health impact. As we can see the emphasis is on maximizing the air quality perception, not the health of the building occupant.
The science of clean air is still evolving. There is no standard definition of “clean air”. Scientific studies have focused on specific issues related to the ambient air such as the effects of radon, formaldehyde, sick building syndrome, air particulates, VOCs and ventilation. But all these studies were focused on the specific problems noted above. There is no single science branch that addresses all the above factors together as one subject. However, there is mounting evidence of the importance of indoor air pollution and lack of adequate ventilation in establishing a healthy air environment.Getting an Air Quality Monitor for your home is a good first step to improve your indoor air quality.WHAT SHOULD WE DO
From the individual studies we can conclude that to maximize healthy air we should try to achieve the following standards:
1) Our first priority should be to eliminate the fine particles (PM2.5) from the ambient air. These particles are smaller than 2.5 micrometers. Within that group the ultra fine particles, smaller than 0.1 micrometers, are the most harmful since studies show that they can easily trans locate from lungs to the blood system.
2) Eliminate environmental tobacco smoke (ETS). Do not smoke indoors!
3) Although there are not many studies on the health effects of inhaled biological particles or the various VOCs present indoors, it is common sense to eliminate as many VOCs from our indoors environment. These include fragrances, formaldehyde and other emissions from building materials.
4) Keep CO2 concentration below 1000 ppm.
5) Homes should be ventilated, as a minimum, at a rate of 7.5cfm (cubic feet per minute) per person plus 3 cfm per 100 square feet of the home.
These are general rules. A study from the Technical University of Denmark  sets the following goals for Indoor Air Quality in the 21st Century.
– Unnecessary indoor pollution sources should be avoided.
-The air should be served to the occupants cool and dry.
– “Personalized air”. Clean air should be introduced close to the breathing zone of each individual.
We certainly want a comfortable indoor environment so we should set our Air Conditioning accordingly. But we also want healthy air. Although the science for clean air is still evolving we should implement the common sense guidelines shown above. As a next step we may want to test our air quality to make sure that we are safe. Click here to find more about testing air quality..Clean air in our homes is our individual responsibility. Following the recommendation of the Technical University of Denmark we should provide personalized clean air by locating air purifiers in the proximity of the occupants if possible, or at least in the kitchen, living room and bedrooms where many of the indoor pollutants originate.
 Impact of indoor air temperature and humidity in an office on perceived air quality, SBS symptoms and performance. L.Fang et al., International Centre for Indoor Environment and Energy. Technical University of Denmark. 2004
 Association of Ventilation Rates and CO2 Concentrations with Health and Other Responses in Commercial and Institutional Buildings. O.A.Seppanen et. al, Wiley Online Library 2004
 A new approach for indoor climate labeling of building materials- emission testing, modeling, and comfort evaluation.Peder Wolkoff,Peter A.Nielsen in Atmospheric Environment Volume 30, Issue 15,August 1996
 Indoor Air Quality in the 21st Century: Search for Excellence/ P. Ole Fanger, Indoor Air/Volume 10,Issue 2., December 2001.