Research on CO2 and Health

Characterizing the relationships between building occupants and indoor carbon dioxide around a wide range of concerns.

Status: Current

Funding Sources: SinBerBEST U.S. General Services Administration U.S. Department of Energy

Categories: Indoor Environmental Quality | Air Quality | Health | HVAC Systems

Project Objective

This research program seeks to understand and characterize the relationships between building occupants and indoor carbon dioxide (CO2) by investigating a wide range of concerns, including CO2 emission, concentration within spaces, and physiological impacts. The work aims to inform indoor air quality standards and ventilation strategies to better protect human health, well-being, and cognition in contemporary home and work environments.

Project Results

These studies collectively demonstrate that indoor CO2 exposure is a dynamic and localized phenomenon. Rising outdoor CO2 levels will inevitably increase indoor concentrations, potentially compromising respiratory health and cognitive function, particularly in poorly ventilated environments. A key finding is the existence of a personal CO2 “cloud,” showing that individuals breathe in significantly higher concentrations of CO2 than ambient room sensors suggest. Furthermore, human emission rates are not static; they fluctuate based on physical and mental activity levels. Ultimately, the research suggests that current ventilation standards must evolve from general room-based metrics to more personalized, activity-driven strategies to ensure occupant well-being.

A key finding is the existence of a personal CO2​ "cloud," showing that individuals breathe in significantly higher concentrations of CO2 than ambient room sensors suggest. Ultimately, this research suggests that ventilation standards must evolve towards more personalized, activity-driven strategies to ensure occupant well-being.

Significance to Industry

Research has shown that elevated exposure to CO2 is linked to poor air quality perception, acute health symptoms, impaired work performance, and increased absence from schools and sick leave from workplaces. Because CO2 is exhaled by occupants, it may be a proxy for ventilation effectiveness, and also the potential presence of other pollutants.  Additional gaseous or particle-phase compounds resulting from human metabolism include volatile organic compounds (VOCs), and bioaerosols. These compounds, emitted via human breath and skin, also impact indoor air chemistry and contribute to degraded indoor air quality.  In addition, rising atmospheric CO2 levels have raised concerns regarding the negative effects on humans and consequently the future of building ventilation. This opens the question regarding whether we can continue to guide ventilation requirements by the difference between outdoor and indoor CO2 levels, or whether absolute CO2 levels should be followed.

Research Approach

Our research approach includes a number of studies with human subjects, many in controlled environments but also using personal monitoring devices in homes, outdoors and in transit.

Respiratory Performance of Humans Exposed to Moderate Levels of Carbon Dioxide

Under some future scenarios, atmospheric CO2 concentration could reach 950 parts per million (ppm) by 2100. Indoor CO2 concentrations will rise consequently, given its relationship to atmospheric CO2 levels. If buildings are ventilated following current standards, by the next century indoor CO2 concentration could reach over 1300 ppm, under some ventilation codes, possibly resulting in negative effects on occupants. We conducted a randomized, within-subject study, examining the physiological effects on the respiratory functions of 15 subjects. We tested three exposure levels, with CO2 of 900 ppm (reference), 1450 ppm (decreased ventilation), and 1450 ppm (reference with added CO2). We measured respiratory parameters including tests of forced vital capacity (FVC) which measures how much can be forcefully exhaled after taking a deep breath. We found that FVC decreased significantly only at the reduced ventilation condition (p < 0.04, a large effect size). This effect is probably not caused by increased CO2 alone but rather by other pollutants, possibly human bioeffluents that were increased from the reduced ventilation.

Personal CO2 Cloud: Laboratory Measurements of Metabolic CO2 Inhalation Zone Concentration and Dispersion in a Typical Office Desk Setting

In this study, the concentration of metabolic CO2 was continuously measured in the inhalation zone of 41 subjects performing simulated office work. The measurements took place in an environmental chamber with well-controlled mechanical ventilation arranged as an office environment. The results showed the existence of a personal CO2 ‘cloud’ in the inhalation zone of all test subjects, characterized by the excess of metabolic CO2 beyond the room background levels. For seated occupants, the median CO2 inhalation zone concentration levels were between 200 and 500 ppm above the background, and the third quartile up to 800 ppm above the background. Each study subject had distinct magnitude of the personal CO2 cloud owing to differences in metabolic CO2 generation, posture, geometry, and breathing patterns. A small desktop oscillating fan proved to be suitable for dispersing much of the personal CO2 cloud, thus reducing the inhalation zone concentration to background level. The results suggest that background measurements cannot capture the effects of CO2 on building occupants.

Real-time Monitoring of Personal Exposures to Carbon Dioxide

Using portable monitors, we conducted an exposure study with 16 subjects in Singapore to understand the levels, dynamics and influencing factors of personal exposure to CO2. Participants carried a CO2 monitor continuously for seven-day periods recording their exposure levels at one-minute intervals. A recall diary was maintained of time-microenvironment-activity budget. We found that the mode of bedroom ventilation was a major determinant of CO2 exposure. Approximately half of the participants slept in bedrooms employing ductless split air-conditioners (group ‘AC’); half slept in bedrooms naturally ventilated through operable windows (group ‘NV’). Median CO2 exposure levels for AC vs. NV groups are significantly different. Mean daily integrated exposures for group AC were statistically higher than for group NV; also events associated with potential adverse cognitive implications (over 2.5 hours at levels over 1000 ppm) occurred more frequently for AC participants and for NV participants. The majority of such events occurred in the home (86%), followed by work (9%) and transit (3%).

Impact of Cognitive Tasks on CO2 and Isoprene Emissions from Humans

The human body emits a wide range of chemicals, including CO2 and isoprene. To examine the impact of cognitive tasks on human emission rates of CO2 and isoprene, we conducted an across-subject, counterbalanced study in a controlled chamber involving 16 adults. In groups of four, participants engaged in 30 min each of cognitive tasks (stressed activity) and watching nature documentaries (relaxed activity). Measured biomarkers indicated higher stress levels were achieved during the stressed activity. Per-person CO2 and isoprene emission rates were greater for stressed than relaxed activity. These results suggest a need to consider cognitive tasks when determining building ventilation rates.

Publications and Reports