Indoor air quality, temperature and cognitive performance

The indoor environmental quality of buildings has a profound impact on
occupants* cognition and health. Humans living in developed economies spend
nearly 90 percent of their time indoors, either working, sleeping or following
recreational activities. The indoor environment became an important factor with
a large body of evidence emphasizing the strong impact buildings have on
workers* productivity. Western economies shift their production capital more
and more towards services, thus knowledge workers, who create value with their
brain power, become an increasingly important production factor for these
economies. Studies have shown that the indoor environment in school buildings
has a strong effect on the academic performance of university students and
pupils at school. Suboptimal indoor air quality and thermal environment hence
may impair academic achievements, which can decrease human capital
accumulation, earning potential and job market success later in life. Thus,
real estate developers, architects and health scientists examined the effect
the indoor air quality and indoor thermal environment have on human cognitive
performance. Past research reveals that a low supply of fresh outside air into
buildings lead to the accumulation of carbon dioxide and other air pollutants
emitted by the occupants and the building environment itself. Mechanical
ventilation is often not provided in buildings in Europe, especially for older
buildings. It has been shown that humans sitting in insufficiently ventilated
rooms show poorer cognitive performance than their counterparts sitting in
rooms with higher ventilation rates. Additionally, evidence from literature
shows that higher temperatures can also negatively affect human cognitive
performance. In the last decades, more frequent, longer lasting and extremer
heat waves have been recorded in Europe. Because only a small share of the
office and school building stock in Europe is equipped with air conditioning,
most occupants have to withstand uncomfortable heat indoors in office and
school buildings during such heat waves. The lack of air conditioning and
mechanical ventilation can lead to profound trade-offs that building occupants
have to make, when outdoor temperatures rise in summer and during heat waves.
On the one hand, they could keep the windows open to ensure good air quality,
but this allows hot air to enter the room and (further) heat it up. On the
other hand, if the windows are kept closed, hot air stays outside, however,
carbon dioxide and air pollutants accumulate inside. Depending on the
insulation level and building materials used, the building will heat up slower
or faster, when outside temperature and sun radiation levels stay elevated over
several days. In combination, without appropriate access to mechanical cooling
and (natural) ventilation, this leads to poor air quality and elevated
temperature indoors. Even though this trade-off is a well-known issue in the
indoor environment sector, only few studies have examined the interaction
effect of bad air quality and high temperature on humans. Most of these studies
included perceived air quality and comfort as the main outcome, showing that
higher temperature modulates the perception of air quality negatively. However,
little is known about this interactive effect with regards to cognitive
performance.

This study aims to examine the interactive effect of indoor air quality and
temperature on human cognitive performance. The main research objective of this
study is to examine how poor indoor air quality in terms of 900 ppm CO2
compared to 3,000 ppm and elevated temperature of 35°C compared to 23°C affect
cognitive performance, respectively. Furthermore, it will be examined if a
higher temperature of 35°C compared to 23°C amplifies the negative effect of
poor air quality in terms of 3000 ppm CO2 concentration vs. 900 ppm CO2
concentration on cognitive performance?

A cross-over single-blinded treatment design will be used. Subjects will
undergo four difference conditions ((1) 900 ppm CO2 and 23°C, (2) 900 ppm CO2
and 35°C, (3) 3,000 ppm CO2 and 23°C, and (4) 3,000 ppm CO2 and 35°C). Subject
will be blinded to the air quality level; however, it is not possible to blind
them to the temperature condition due to its easy detection.

Each subject undergoes four conditions in randomized order. Two conditions
consist of poor air quality defined as 3000 ppm carbon dioxide and 23°C or 35°C
temperature, respectively. These two temperature conditions will be repeated,
but then with good air quality defined as 900 ppm CO2.

Subjects have to come once for a screening session and then for the four
testing conditions to the MRUM lab facilities. They will stay in the
respiration room for eight hours on each test day. They have to conduct
cognition tests two times a day and fill out questionnaires about their
perception of the indoor environmental quality.