By Capt. William Taylor, USAF, Lisa Brenner, and Lt. Col. Andrew Hoisington, Ph.D., P.E., M.SAME, USAF

Air quality is often referenced as having health implications, yet many may not understand the mechanisms behind those health effects. Atmospheric air is naturally composed of a handful of elements, including nitrogen, oxygen, argon, carbon dioxide, and trace amounts of other gases. Over time, anthropogenic activities have increased a few of these trace gases to potentially harmful levels. In the mid-20th century, scientists and healthcare researchers recognized the effects that some of these gases were having on humans. The Clean Air Act of 1963 was passed as a result, and enforcement eventually fell under the Environmental Protection Agency (EPA).

EPA has identified six pollutants to regulate, including sulfur dioxide, carbon monoxide, ozone, nitrogen dioxide, lead, and particulate matter. Of these, particulate matter (PM) currently shows the most consistent relationship with health effects.

POLLUTANT OF INTEREST

PM refers to small particles of solid or liquid matter prevalent in the air. These include dust, bacteria, smoke, ash, smog, and heavy metals, and they can originate naturally or be man-made. Common sources include wildfires, dust storms, industrial activities, construction or demolition, and the burning of fossil fuels. PM is categorized into three groups based on size: PM₁₀ consists of particles smaller than 10-μm; PM₂.₅ is smaller than 2.5-μm; and PM₀.₁ is smaller than 0.1-μm.

Adverse Health Effects. Researchers estimate that in 2015, PM₂.₅ caused 4.2 million deaths worldwide, making it the fifth highest mortality risk factor. In particular, there is a connection between PM₂.₅ exposure and cardiovascular or respiratory diseases, such as lower respiratory infection, lung cancer, ischemic heart disease, cerebrovascular disease, and chronic obstructive pulmonary disorder. Additionally, PM₂.₅ can exacerbate asthma conditions and contribute to the onset of bronchitis. By penetrating into the lungs and depositing into the alveoli and bronchioles, or entering into the bloodstream, chronic PM₂.₅ accumulation can result in these health risks through a variety of biological mechanisms.

Academic research has also shown that PM₂.₅ is associated with a reduction in cognitive function. PM deposits in the body can lead to chronic inflammation, which is associated with cognitive decline. A study of elderly adults showed that general cognition, attention, and memory scores declined at faster rates where PM concentrations were higher. Some preliminary studies have even linked PM₂.₅ exposure as a risk factor for Alzheimer’s disease. Autopsies of deceased individuals living in cities with high PM₂.₅ concentrations showed biologically relevant inflammatory markers regularly associated with Alzheimer’s. The mechanism behind this relationship is unclear, but one theory suggests that chronic inflammation of the respiratory tract alters the levels of certain proteins within the bloodstream that cause the brain to develop chronic inflammation.

Mental Illness Concerns. A growing body of research is also working to connect PM₂.₅ exposure to mental illnesses. Anxiety, depression, and suicide all have population-level studies that show association with PM₂.₅ exposure, with both impacts being acute and chronic exposure. Researchers have used geographical information systems to measure and model concentrations in specific areas and compare PM levels with the mental health records of patients. For example, a study of more than 70,000 women found that symptoms of anxiety were higher in women who lived in areas of higher PM₂.₅ concentration. Research in South Korea identified long-term PM₂.₅ exposure as a risk factor for depression as well as suicide. Large spikes in the measured PM₂.₅ concentrations increased the risk of suicide by 9 percent within the next two days, especially among individuals already suffering from a cardiovascular disease.

Commonly cited theories for the biological connection between mental health and PM₂.₅ include chronic inflammation and oxidative stress, which is an imbalance of certain chemicals within the body. Oxidative stress and chronic inflammation have been shown to correlate with depression and other mental health outcomes.

For veterans and active duty members of the military, additional concerns are present. Veterans experience post-traumatic stress disorder and other mental health challenges at a higher rate than civilians. Aside from the traumas and stressors of military life, the different environmental factors that military members are exposed to could be influencing this higher rate of mental illness. For instance, deployments to the Middle East expose personnel to higher concentrations of ambient PM in the form of dust.

DESIGNING FOR HEALTH

Even though most of the PM₂.₅ that is harmful to humans is generated by outdoor sources, the majority of our exposure comes through time within buildings. Generally, PM₂.₅ penetrates through leaks in the building envelope and is recirculated indoors by the HVAC system (though there are some common indoor activities that can generate PM₂.₅ as well, such as smoking, cooking, and cleaning). While engineers and architects have little to no control over the outdoor concentrations of PM₂.₅, design and construction decisions can be made that promote the reduction of this harmful pollutant within the confines of the built environment.

As PM₂.₅ enters buildings through leaks in the building envelope, higher Minimum Efficiency Reporting Value (MERV) filters can reduce the amount that circulates through the HVAC system. Higher MERV filters are more expensive than the minimum MERV 6 filter that ASHRAE recommends. Benefit/cost analysis studies, however, show that the increase in price is more than warranted by the reduction in costs due to health effects. Installing these filters is an important first step in eliminating a large portion of indoor PM₂.₅.

Architects and engineers can take further steps in eliminating PM exposure indoors through design and construction techniques that eliminate infiltration, which happens when PM passes through small openings in the building envelope.

The Air Force Institute of Technology and the Department of Veteran Affairs Rocky Mountain Mental Illness Research Education Clinical Center have partnered to study the impact that the built environment has on military personnel. Veterans and active duty members have been surveyed to compare aspects of their residences to their mental health state. Identifying trends may reveal specific elements that are having effects on mental health, and future design and construction standards can use this information to positively impact the mental health of building occupants.

A POSITIVE STEP FORWARD

Engineering professionals can have a measurable impact on indoor air quality through implementation of tactics in facilities, as well as through supporting policy that reduces PM₂.₅ and other airborne pollutants worldwide. Improved standards for industrial and auto- mobile emissions could reduce PM₂.₅ concentrations. In developing countries, finding ways to supply citizens with electricity would eliminate the emissions created from burning biomass. Lastly, formulating effective strategies for preventing and containing wildfires would reduce ambient PM₂.₅ in certain environments.

These choices can have a positive impact on the physical, cognitive, and mental health of building occupants—especially those serving the U.S. military, as their geographical and mission-related requirements put them at a greater risk level. Providing awareness of the impact air quality has upon health is the first step, and promoting healthy buildings through design choices is the next.


Capt. William Taylor, USAF, is Graduate Student, and Lt. Col. Andrew Hoisington, Ph.D., P.E., M.SAME, USAF, is Associate Professor, Department of Civil & Environmental Engineering, Air Force Institute of Technology. They can be reached at william.taylor.93@us.af.mil; and andrew.hoisington@us.af.mil.
Lisa Brenner, Ph.D., is Director, Rocky Mountain Mental Illness Research Education Clinical Center, Department of Veterans Affairs; lisa.brenner@va.gov.

[This article first published in the January-February 2021 issue of The Military Engineer.]