Beyond Green Award Winner

Indoor Air Quality Research

General Information


SOM is advocating a new generation of buildings to provide occupants with clean air. The conventional practice on natural ventilation focuses on the thermal comfort of the occupants- windows are opened with little regard to how clean the outside air is. The majority of the people in the world have the perception that outdoor air is cleaner than indoor air. SOM has studied air quality around the world for more than two years. From this work, it is clear that outdoor air in many cities around the world may not be cleaner than indoor air at any given time. To achieve clean indoor air will require either closing windows or additional filtering. We need to educate and inform billions of occupants around the world about local air quality, and opening windows should address both thermal and contaminant needs. One of the contaminants to be addressed is PM 2.5. High ambient PM 2.5 can adversely impact buildings and building occupants in several ways.

Added air filtration systems are often necessary, extra pressurization is often utilized to offset outdoor air infiltration, and natural ventilation opportunities are often diminished. Combined, these factors contribute to diminished indoor air quality and increased overall energy consumption. This methodology provides healthy air in 3 steps:

  1. It monitors indoor air and local outside air quality through smart air quality sensors.

  2. It provides the information to occupants informing them when windows should be opened. It does this through a tenant dashboard, building websites, and green light (window can be opened)/red light (window should be closed) sensors.

  3. It adds special HVAC systems to filter both intentional outside air intake and unintentional air infiltration as required (Fig. 1).

air quality sensors and window open/closed indicators

Fig. 1

Purpose of the innovation.

Out of all air contaminants, PM 2.5 impacts a significant portion of the world's population (Fig. 2): according to NASA satellite data, it influences close to 60–70% of all people. Many, however, believe that outdoor air is cleaner than indoor air—"fresh air," as it refers to outdoor air, is a common misnomer. Culled from two years of study, SOM has determined that PM 2.5 contaminant levels fluctuate; many times they surpass levels deemed healthy by government agencies, health protection advocates, and scientific researchers. It is SOM's belief that a new generation of building system design and operations-one that prioritizes smart natural ventilation and mechanical filtration—will drastically improve indoor air quality. Going beyond design interventions, SOM also believes education is key. By informing people about PM 2.5 contaminant levels and by providing tools to strategically manage their impact, air contaminant stressors will be reduced indoors.

satellite-derived map of PM 2.5 distribution around the world

Fig. 2

Building types to which it can apply.

SOM's study and methodology can be applied to all building types.

Participants in its development or implementation.

Skidmore, Owings & Merrill LLP Sustainable Engineering Studio, Luke Leung, PE, LEED AP (BD+C), Sergio Sabada, PE, CEng MCIBSE, Jason Kirkpatrick, LEED AP (BD+C), Ray Clark, Fellow

Cost of implementation.

$20,000 sensor installation and 2% energy increase.


How the innovation came to be developed, and how the innovation addresses a specific issue faced by the industry.

In 2007, the U.S. Federal government commissioned SOM to design a building; falling in line with government parameters, SOM equipped the structure with outdoor air censors. After the building was completed, SOM designers were astonished to find that the outdoor censor readings captured PM 2.5 contaminant levels exceeding 800 µg/m3. This level is almost 23 times the 35 µg/m3 limit, a safety standard set by ASHRAE. This is alarming, as air is the simplest element for health—we need it to breathe from the moment of birth until death.

SOM's data echoed findings presented in the American Lung Association's "State of the Air 2010," a report that paints a broader picture of rampant air contamination. The study found that in 2010, over 175 million people—roughly 58% of the U.S. population—suffered pollution levels that were often too dangerous to breathe, and roughly one in ten people—23.8 million—live in areas contaminated with unhealthy, year-round PM 2.5 levels. Spurred on by these observations, SOM's Sustainable Engineering Studio traveled to different cities around the world in order to measure global PM 2.5 contaminant levels. Readings in many cities, from Beijing, Dubai, Delhi, Chicago, to Shanghai, Shenzhen, etc. came back with readings that exceed standards.

Popular public perception contradicts these facts. Universally, outdoor air is still considered the most "fresh," and building occupant habits and building codes still follow this belief. Even official sustainability standards, such as in the Living Building Challenge, advise that "every occupiable interior space must have operable windows that provide access to fresh air." SOM determined that a new methodology must be developed in order to improve indoor air quality and change popular beliefs. SOM's case study "Impact of PM 2.5 on Low Energy Buildings and Indoor Air Quality" develops and explains this methodology in detail. This study's findings support both the implementation of smart mechanical filtration and informed natural ventilation practices as well as the monitoring of increased energy consumption caused by added filtration technologies. It is hoped that by sharing this methodology with systems and building design engineers worldwide, significant progress will be made toward managing indoor PM 2.5 contaminant levels.

Current practices and why this one is superior to others.

This new methodology is superior to current practices in two ways:

  1. During natural ventilation mode: It will inform the building occupants when the outside air is appropriate for opening windows.
  2. During mechanical mode: Proper filtering is important for control of outside air.

If the ambient PM 2.5 is too high and the filtration devices are not selected properly, the PM 2.5 levels inside the building can be higher than recommended. SOM developed a methodology to mitigate this issue. The filtering methodology is documented in SOM's Beijing case study "Impact of PM 2.5 on Low Energy Buildings and Indoor Air Quality." This is one of the first papers presented that examines how PM 2.5 contaminant levels adversely affect indoor air quality. It was presented at the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Indoor Air Quality Conference in Vancouver, Canada in October, 2013. It provides a methodology on how to improve indoor air quality accordingly. It outlines pertinent observations and a new research methodology for collecting and analyzing PM 2.5 data that can be used to improve system design, air filtration, and natural ventilation practices.

The research methodology, much like the implementation methodology, breaks down into two steps:

Step One: Establish PM 2.5 Profile and Design Criteria

Of the multiple PM 2.5 measurement stations in Beijing, SOM found that the U.S. Embassy station recorded the worst PM 2.5 levels, and thus its data was used in the study (Fig. 3). An 8,760 hour profile of PM 2.5 was recorded for Beijing (Fig. 4). A design criteria nomenclature of 0.40% was developed by analyzing the data, meaning that for 0.40% of the total annual hours, PM 2.5 counts measure above 480 µg/m3.

Bar graph of PM 2.5 impact indoor air quality

Fig. 3

Scatter graph summarizing the 8,760 hours contaminating profile in Beijing

Fig. 4

Step Two: Analyze the Effect of Various Filter Efficiencies

Proper filtering is important in order to control PM 2.5 levels inside a building. If the ambient PM 2.5 is too high and the filtration devices are not selected properly, the PM 2.5 levels inside the building can be higher than recommended. Current ASHRAE 62.1-2010 recommends: " When the building is located in an area where the national standard or guideline for PM 2.5 is exceeded, particle filters or air cleaning devices shall be provided to clean the outdoor air at any location prior to its introduction to occupied spaces. Particulate matter filters or air cleaners shall have a Minimum Efficiency Reporting Value (MERV) of 11 or higher when rated in accordance with ASHRAE Standard." Selecting correct filters that achieve at least MERV 11 requires a study of the site's PM 2.5 air quality profile. The required filters may increase the mechanical system's energy consumption. SOM simulated three standard filters with Dedicated Outdoor Air System (DOAS) unit: MERV 12, MERV 13, and MERV 14. The MERV 12 resulted in a PM 2.5 discharge condition of 196 µg/m3; the MERV 13 resulted in a PM 2.5 discharge condition of 65 µg/m3; and the MERV 14 resulted in a PM 2.5 discharge condition of 58 µg/m3.

All three PM 2.5 results measured well above the ASHRAE Standard of 35 µg/m3 (Fig. 5). The HVAC unit operates as a single pass-through filter system; in fan coil systems, filters in each fan coil re-circulate air, resulting in multiple pass-throughs. To account for these differences, SOM also simulated five combinations of DOAS and fan coil filter efficiencies tested at three different infiltration rates: 0.0 air changes per hour, 0.1 air changes per hour, and 0.25 air changes per hour. The combined results produce a better study of the resultant indoor air quality (Fig. 6). Infiltration significantly impacts PM 2.5 levels in the indoor air. SOM found that outdoor air essentially bypasses the DOAS unit, bringing unfiltered PM 2.5 into the building. As expected, as infiltration rates increase, both fan coil filters and DOAS filters need to achieve higher efficiency in order to maintain acceptable indoor air PM 2.5 (Fig. 6). SOM's findings also suggest that the HVAC system can be used to pressurize the space in order to further reduce infiltration and maintain acceptable indoor air quality.

tables depicting the comparison oh filters at the HVAC unit to meet 35µg/m3

Fig. 5

tables depicting the simulation of various combinations of outdoor air AHU and fan coil filter efficiencies to achieve 35 micro;g/m3

Fig. 6

Positive and negative aspects of the innovation.

By improving both mechanical systems and natural ventilation usage, overall indoor PM 2.5 contaminant levels can be drastically reduced. However, the installation and implementation of these systems can have a cost impact. SOM found that sensor material and installation cost on average $20,000, while incremental filtering costs and building energy operating costs increased by 2%.

Criteria Objectives

Whole Building Design Objectives. The high-performance attributes the innovation addresses.

Nearly 2,000,000 people worldwide have died due to PM 2.5. (Global premature mortality due to anthropogenic outdoor air pollution and the contribution of past climate change). SOM's methodology can inform and create a healthier environment for the global population. It is an accessible technology since it is aimed at occupants; even those who are hearing impaired can see the "red/green" lights before opening windows. The technology is relatively low cost when its benefits are considered. It safeguards the public against contaminants that exceed current standards. It satisfies a functional need of measuring PM 2.5 that currently does not exist in our industry, and it links this need to the important element of operable windows. It improves the well-being of the occupants and potentially increases their productivity by improving their living environment, thereby possibly improving their health.

Benefits to the owner/client and the industry as a whole. Uniqueness of the solution, how this innovation differs from current practice, and how the innovation addresses a specific issue being faced by the industry.

SOM's study benefits the design industry at two levels. More specifically, it provides a new research and implementation methodology to system and building engineers who are also working to improve indoor air quality. More broadly, it frames an argument that questions the misconception that "fresh air" is optimal air, and establishes solid research groundwork that can be further tested and refined in future air quality studies.

Replicability or Applicability. How easily the innovation can be utilized on other projects. Innovation. Unique aspects of the product and any innovative problem solving.

Although SOM's study focuses on managing PM 2.5 contaminant levels, the methodology is applicable to other contaminant examinations, including PM 10, ozone, CO, NOx, SOx, lead, and others. SOM hopes that researchers working on similar contaminant studies adapt the PM 2.5 methodology to best fit and advance their research.


SOM's study engages not only systems and building engineers, but also allied scientists working on similar projects and building occupants at large. From the study's outset, SOM intended to provide a methodology that is easy to understand, easy to implement, and easy to adapt. SOM also intended to shift the general belief that outdoor air is "fresh air" by making air quality problems visible to non-specialist building occupants. The simple, user-oriented technologies that indicate air quality levels achieve this goal, sparking a new awareness about air quality and the impact it can have on indoor space.



  • Merit Award: Category E: Innovations for High-Performance Buildings, 2013 Beyond Green Award of the Sustainable Buildings Industry Council.
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