The Time is Now

The people who design, operate and manage buildings are instrumental to realizing healthy indoor air. Unlike water, which is purified at a central location and then distributed, air is treated onsite. Common air management strategies include ventilation, filtration and UV air disinfection. There is concern about the cost and energy impacts of these strategies, and a perception that buildings cannot be simultaneously healthy, green and energy efficient. One way to get sustainable, clean air is to monitor indoor air quality and adjust building operations to provide appropriate where people are (e.g. using demand-control ventilation). A limitation of this approach is that today, indoor air quality is based on measuring particles and chemicals (e.g. fine particulate matter and carbon monoxide), which do not provide data on pathogen and allergen loads and lack a direct connection to microbial exposure risk. Another limitation is the historical disconnect between public health and building science, which has contributed to a lack of microbiology-informed IAQ standards.

What if air quality biosensors operated like thermostats?

Indoor air is teeming with tiny organisms invisible to the naked eye, including viruses, bacteria and molds. Scientists have estimated that a single cubic meter of indoor air contains hundreds of thousands of virus-like and bacteria-like particles, and approximately 100 mold “colony forming units” (CFUs). Indoor microbes derive from many sources, including people, pets, plants, plumbing systems, heating, ventilation, and air-conditioning (HVAC) systems and outdoor air. Given the average adult inhales approximately 16 cubic meters of indoor air daily, it stands to reason indoor air microbes have a profound impact on human health. While they can be pathogenic and infectious - causing Aspergillosis, Legionnaires' disease, colds, flus, COVID-19 and other health issues - the majority are harmless and some are even beneficial to human health.

Managing the microbes of daily life requires measuring them. The industry lacks accessible tools for directly measuring the concentrations of microbial species known to impact human (and building) health. As a consequence, during the COVID-19 pandemic, proxies like CO2 monitoring, which is relatively inexpensive and essentially provides real-time data, emerged as an approach to assess indoor infection risk. CO2 levels build up when people exhale indoors but can remain low if a space is well ventilated, and research suggests that low ventilation rates (measured using CO2 as a proxy) negatively impacts cognitive function and productivity. Given CO2 levels are used as an indicator of ventilation, by extension, it has been reasoned they can be used as an indicator of the risk that SARS-Cov-2 (the virus that causes COVID-19) might be accumulating indoors. But CO2 measurements cannot indicate if an infected person is in the room, the amount of airborne viral particles produced by infected people, or whether intervention strategies are effective at reducing or removing infectious pathogens and other harmful bioaerosols.

To overcome these limitations, scientists have been working to adapt gold standard human diagnostic tools for indoor air. During the COVID-19 pandemic, diagnostics like antigen tests and molecular tests became household terms. Often referred to as rapid tests or, for some, at-home or self tests, antigen tests work by detecting proteins called antigens from viruses like SARS-CoV-2. Molecular tests like polymerase chain reaction (PCR) are considered the most sensitive for detecting viruses and work by amplifying - or making many copies of - the virus’ genetic material, if any is present on a specimen or sample (e.g. a nose swab). The remarkable sensitivity of PCR-based techniques has long been recognized as powerful for air analysis, given that air holds miniscule amounts of microbiological material. As an example, there are many orders of magnitude more SARS-CoV-2 in a milliliter of saliva sampled from a COVID-infected patient relative to a milliliter of air sampled near the same patient. Another benefit of PCR is that it can be applied to detect and measure any biological matter that contains nucleic acids such as viruses, bacteria, mold, pollen or dust mites.

Despite decades of air molecular diagnostics research, broad adoption has been constrained by user experience, turnaround time and cost. The U.S. Department of Homeland Security BioWatch Program, which invested significant time and money to develop outdoor air sensors for biosecurity, created PCR systems that required manual intervention and sending samples back to a laboratory. Commercially available PCR systems also do not integrate detection with collection; this lack of autonomy requires trained staff onsite to process samples and increases turnaround time. These limitations can be overcome, as evidenced by an early stage venture-backed company that developed prototypes of a fully automated air to PCR desktop biosensor for SARS-CoV-2 detection. Prototypes were created with a modest budget and less than 18 months, providing proof of concept that disruptive advances in user experience and turnaround time are within reach. Informational interviews with design and engineering teams suggest that dramatic instrumentation and cost reductions can be achieved, making air quality biosensors accessible to all, in a few years with modest investment.

What if buildings could be adapted for clean air?

More than 150 years ago, it became well understood that clean drinking water and adequate sanitation are required to control cholera and other waterborne diseases. In 1963, the U.S. Clean Air Act was established to protect humans and the environment from outdoor air pollution. Today, scientists are advocating for an indoor version of the bill and the development of IAQ guidelines and standards for airborne infectious disease.

Multiple factors have contributed to disparity in the management of airborne infectious disease relative to waterborne and foodborne disease. One factor is sociological, described as a longstanding aversion by the medical establishment to airborne transmission theories, due to misleading “miasma” theory that prevailed for much of the 19th century. Miasma theory came before germ theory (which was scientifically informed by equipment such as the microscope) and posited that smelly air (versus germs) caused cholera and other diseases. Even after miasma theory was discredited by germ theory, the medical establishment fixated on “contact transmission” (i.e. transmission through direct contact and close proximity), and largely dismissed airborne transmission and the reality that infection by germs can also come from the environment. Fast forward to the 21st century, an era where it took two years into the COVID-19 pandemic before the World Health Organization (WHO) classified SARS-CoV-2 as airborne. Contributing to this lag was a lack of knowledge of aerosol science by the medical and health communities and limited research on airborne transmission, coupled with a lack of tools to easily and reliably measure airborne microorganisms.

Autonomous and cost-effective air quality biosensors will provide information needed to effectively manage airborne microbes. As a first step, quantifiable links between indoor bioaerosol concentrations and health risks need to be established. There is literature on airborne disease transmission and models for estimating infection risk in the built environment (e.g. Safe airspaces COVID-19 Aerosol Relative Risk Estimator). However there remain tremendous knowledge gaps about indoor microbial transmission, exposure, and risk. Bridging this gap will require better tools for monitoring the source and prevalence of airborne pathogens and allergens.

Another driver of IAQ will be the expansion of guidelines and standards to include microbiology. In 2021, scientists urged WHO to expand IAQ guidelines to include airborne pathogens and ASHRAE to development ventilation standards to mitigate infection risk. In 2022, the Biden-Harris Administration announced the Clean Air in Buildings Pledge followed by commitments including tax credits, research funding, and a plan to establish approximately 1,500 federal buildings as an exemplar of IAQ standards. ASHRAE in turn committed to an aggressive six-month timeline to support development of a national indoor air quality pathogen mitigation standard.

Collectively, these efforts reflect a growing recognition that clean and safe indoor air - while invisible -is essential to public health, biosecurity and the economy. The U.S. Environmental Protection Agency recently published a best practices guide aimed at helping facility managers improve IAQ, with baseline recommendations like increasing ventilation and maximizing outdoor air, upgrading to MERV-13 filters, and commissioning (i.e. giving buildings a “tune-up”) to ensure building systems are functioning as designed. By June 2023, ASHRAE will publish new ventilation standards for infection control, which are expected to be adopted as code. Advances in smart building environmental sensor platforms that track CO2, particulates, and volatile organic compounds are laying the foundation for real-time air quality monitoring. In the not-too-distant future air biosensors will be included in these platforms, and used for assessing building performance and benchmarking (similar to energy benchmarking), validating the efficacy and safety of air cleaners, informing public health early warning systems, and applications that cannot be imagined today.