Ausgewählte Studien

This study monitored indoor environmental data in 144 classrooms in 31 schools in the Midwestern United States for two consecutive days every fall, winter, and spring during a two-year period; 3,105 pupils attended classrooms where the measurements were conducted. All classrooms were ventilated with mechanical systems that had recirculation; there were no operable exterior windows or doors. The daily absence rate at the student level and demographic data at the classroom level were collected. The overall mean ventilation rate, using outdoor air, was 5.5 L/s per person (the corresponding mean carbon dioxide concentrations were < 2,000 ppm), and the mean indoor PM2.5 was 3.6 μg/m3. The annual illness-related absence rate at the classroom level was extracted from the student-level absence data and regressed on measured indoor environmental parameters. Significant associations were found. Every 1 L/s per person increase in ventilation rate was associated with a 5.59 decrease in days with absences per year. This corresponds to a 0.15% increase in the annual daily attendance rate. Every additional 1 μg/m3 of indoor PM2.5 was associated with a 7.37 increase in days with absences per year. This corresponds to a 0.19% decrease in the annual daily attendance rate. No other relationships were significant. Present results agree with the previously demonstrated benefits of reduced absence rates when classroom ventilation is improved and provide additional evidence on the potential benefits of reducing indoor inhalable particles. Overall, reduced absence rates are expected to provide socioeconomic benefits and benefits for academic achievements, while higher ventilation rates and reduced particle levels will also contribute to reduced health risks, including those related to airborne respiratory pathogens.

Background: The indoor built environment plays a critical role in our overall well-being because of both the amount of time we spend indoors (~90%) and the ability of buildings to positively or negatively influence our health. The advent of sustainable design or green building strategies reinvigorated questions regarding the specific factors in buildings that lead to optimized conditions for health and productivity.
Objective: We simulated indoor environmental quality (IEQ) conditions in “Green” and “Conventional” buildings and evaluated the impacts on an objective measure of human performance: higher-order cognitive function.
Methods: Twenty-four participants spent 6 full work days (0900–1700 hours) in an environmentally controlled office space, blinded to test conditions. On different days, they were exposed to IEQ conditions representative of Conventional [high concentrations of volatile organic compounds (VOCs)] and Green (low concentrations of VOCs) office buildings in the United States. Additional conditions simulated a Green building with a high outdoor air ventilation rate (labeled Green+) and artificially elevated carbon dioxide (CO₂) levels independent of ventilation.
Results: On average, cognitive scores were 61% higher on the Green building day and 101% higher on the two Green+ building days than on the Conventional building day (p < 0.0001). VOCs and CO₂ were independently associated with cognitive scores.
Conclusions: Cognitive function scores were significantly better under Green+ building conditions than in the Conventional building conditions for all nine functional domains. These findings have wide-ranging implications because this study was designed to reflect conditions that are commonly encountered every day in many indoor environments.

Die CO₂-Konzentration wird bereits seit mehr als 150 Jahren als Indikator für die Innenraumluftqualität verwendet. Entsprechende Grenzwerte sind in der Gesetzgebung (z.B. Arbeitsstättenrichtlinie (ASR) 3.6) vorgeschrieben. Bei einem längeren Aufenthalt hängt die CO₂-Konzentration mit der Personenanzahl, der Dauer des Aufenthalts und der dem Raum zugeführten Außenluftmenge zusammen. Für kürzere Aufenthalte spielt auch das Raumvolumen eine Rolle. Zusätzlich bieten die CO₂-Konzentration sowie die daraus folgende angenommene mögliche inhalierte CO₂-Dosis die Möglichkeit, verschiedene Situationen hinsichtlich eines relativen Infektionsrisikos durch luftgetragene Pathogene miteinander zu vergleichen. Neben CO₂ geben Personen mit einer viralen respiratorischen Infektion auch virenbeladene Partikel ab, die von anderen Personen im Raum eingeatmet werden. Für die gleiche Menge inhalierter virenbeladener Aerosolpartikel ist bei Verdoppelung der Aufenthaltszeit im stationären Zustand eine Halbierung der CO₂-Konzentration (Differenz zwischen der Innenraum- und Außenluftkonzentration) notwendig. Dies hebt die Bedeutung des Lüftens bzw. des Austauschs der zugeführten Außenluftmenge noch einmal deutlich hervor.

Airborne transmission of SARS-CoV-2 through virus-containing aerosol particles has been established as an important pathway for Covid-19 infection. Suitable measures to prevent such infections are imperative, especially in situations when a high number of persons convene in closed rooms. Here we tested the efficiency and practicability of operating four air purifiers equipped with HEPA filters in a high school classroom while regular classes were taking place. We monitored the aerosol number concentration for particles >3 nm at two locations in the room, the aerosol size distribution in the range from 10 nm to 10 µm, PM10 and CO₂ concentration. For comparison, we performed similar measurements in a neighboring classroom without purifiers. In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90% within less than 30 min when running the purifiers (air exchange rate 5.5 h−1). The reduction was homogeneous throughout the room and for all particle sizes. The measurements are supplemented by a calculation estimating the maximum concentration levels of virus-containing aerosol from a highly contagious person speaking in a closed room with and without air purifiers. Measurements and calculation demonstrate that air purifiers potentially represent a well-suited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially. Staying for 2 h in a closed room with a highly infective person, we estimate that the inhaled dose is reduced by a factor of six when using air purifiers with a total air exchange rate of 5.7 h−1.

The aim of this study was to assess the effectiveness of air cleaning in reducing the risk of respiratory infection in two day care centres using a simple and robust calculation model. Additionally, we aimed to identify potential hotspots for infections in indoor setting and focus countermeasures accordingly. Initial results from an interventional clinical study are provided as proof-of-concept for the model. We constructed a mathematical model to assess the number of persons at risk for airborne infection transmission in day care. Utilizing the model, we used portable air cleaners in two day care units (A and B, number of children participating in the study n = 43) and compared infection incidents between the two intervention units to the rest of the units in city of Helsinki (n = 607). The intervention buildings had mechanical supply and exhaust air ventilation. The risk modelling suggests that the use of air cleaners reduced the expected number of persons at infection transmission risk significantly. At day care centre A the average reduction was 60% (range 52% – 88%) and at day care centre B 53% (range 14% – 59%). During the approximately six month study period, we observed a significant difference in the days absent from day care due to infections between the intervention and reference day care units. On average, the parents were absent from work due to child’s illness in reference day care centers for 5.53 days and 3.77 days in intervention day care centers during the study period (p=0.009). In relative terms the reduction was approximately 32%. Our study offers compelling evidence to support increasing non-infectious air flow rates in daycare centers during periods requiring infection risk management. This can be implemented with portable air cleaners as an effective and cost-efficient strategy for mitigating the spread of respiratory infections among children. The clinical results support the findings suggested by the theoretical model.

In the wake of the COVID-19 pandemic, prioritizing indoor air quality has emerged as a crucial measure for preventing infections. Effective ventilation is vital in mitigating airborne pathogen transmission and maintaining a healthy indoor environment by diluting and removing infectious particles from enclosed spaces. However, increasing the supply of pathogen-free air to enhance infection control can lead to a rise in energy consumption. Nevertheless, evaluating the overall efficacy of ventilation-based infection prevention strategies while considering their energy requirements has posed challenges. This scientific paper introduces the ICEE (Infection Control’s Energy Efficiency) index, a newly developed simple integrated index to assess the effectiveness of ventilation strategies in reducing infection risks while accounting for associated energy demands. The paper reviews the current understanding of ventilation strategies, their impact on infection prevention, and their corresponding energy consumption. By employing a straightforward analytical approach, this metric offers a comprehensive framework to optimize ventilation systems for both infection prevention and energy efficiency. To quantify infection risk, a simplified equation model is utilized, incorporating factors such as ventilation effectiveness and filter efficiency, in case of recirculation. Energy demand is determined using approximations and relevant values from existing literature. Reference cases are defined, distinguishing between natural and mechanically ventilated scenarios, as these reference situations influence the energy-related effects of any implemented measures. The paper outlines the methodology employed to develop the index and illustrates its applicability through exemplary measures. The proposed index yields valuable insights for the design, operation, and retrofitting of ventilation systems, enabling informed decision-making towards fostering a healthier and more sustainable built environment.

Exposure to airborne particles is a serious health concern worldwide and indoor air quality is a critical factor influencing exposure. This work investigates the impact of modified ventilation and filtration system designs to inform building designers, operators, and policy makers of relative effectiveness and costs. Indoor aerosol dynamics, filter cost, and epidemiological models were combined to compare size-resolved indoor particle concentrations, operation costs, and monetized health benefits to occupants within an office building. System airflow and filter efficiency were modified to compare the relative economic implications. Comparisons were made for a number of cities to examine the impact of variation in local air quality, electricity prices, and economic conditions.
The operation cost of filtration systems was found to vary by a factor of 3 between cities. The monetized health benefits of filter installations outweigh the operation costs by up to a factor of 10. In the majority of scenarios investigated the net benefits of improved filtration were greatest for the highest efficiency filters. Adding or increasing recirculated and return air in the system provides a net financial benefit due to (indirect) societal health benefits outweighing (direct) operational costs for small increases in airflow but has diminishing returns for large increases. Though system changes are economically beneficial from a societal viewpoint, the costs and benefits are borne by disparate parties and policy changes may be required to ensure optimum design and operation.

Residential wood combustion contributing to airborne particulate matter (PM10) was studied for 1 year at two sites in the village of Melpitz. Significant excess pollution was observed at the Melpitz center compared to that at the TROPOS research station Melpitz reference site, situated only 700 m away. Local concentration increments at the village site for the combustion PM constituents organic carbon, elemental carbon, levoglucosan, and benzo[a]pyrene were determined under appropriate wind directions, and their winter mean values were 0.7 μg m–3, 0.3 μg m–3, 0.1 μg m–3, and 0.4 ng m–3, representing relative increases over the regional background concentration of 24, 70, 61, and 107%, respectively. Yearly, weekly, and diurnal profiles of village increments suggest residential heating as the dominant source of this excess pollution, mainly originating from wood combustion. Receptor modeling using positive matrix factorization quantified 4.5 μg m–3 wood combustion PM at the village site, representing an increment of 1.9 μg m–3 and an increase of ∼75% over the 2.6 μg m–3 regional background wood combustion PM. This increment varied with season, temperature, and boundary layer height and reached daily mean values of 4–6 μg m–3 during unfavorable meteorological conditions. Potential health effects were estimated and resulted in an all-cause mortality from short-term exposure to wood combustion PM of 2.1 cases per 100,000 inhabitants and year for areas with similar wood smoke levels as observed in Melpitz. The excess cancer risk from the concentrations of polycyclic aromatic hydrocarbons was 6.4 per 100,000. For both health metrics, the very local contributions from the village itself were about 40–50%, indicating a strong potential for mitigation through local-scale policies. A compilation of literature data demonstrates wood combustion to represent a major source of PM pollution in Germany, with average winter-time contributions of 10–20%. The present study quantifies the negative impacts of heating with wood in rural residential areas, where the continuous monitoring of air quality is typically lacking. Further regulation of this PM source is warranted in order to protect human health.

People living in urban and industrialized societies, which are expanding globally, spend more than 90 % of their time in the indoor environment, breathing indoor air (IA). Despite decades of research and advocacy, most countries do not have legislated indoor air quality (IAQ) performance standards for public spaces that address concentration levels of IA pollutants. Few building codes address operation, maintenance, and retrofitting, and most do not focus on airborne disease transmission. But the COVID-19 pandemic has made all levels of society, from community members to decision-makers, realize the importance of IAQ for human health, wellbeing, productivity, and learning. We propose that IAQ standards be mandatory for public spaces. Although enforcement of IAQ performance standards in homes is not possible, homes must be designed and equipped so that they could meet the standards.

Scientific literature and documents pertaining to the effects of inhalation exposure to carbon dioxide (CO₂) on human health and psychomotor performance were reviewed. Linear physiological changes in circulatory, cardiovascular, and autonomic systems on exposure to CO₂ at concentrations ranging from 500 to 5000 ppm were evident. Human experimental studies have suggested that short-term CO₂ exposure beginning at 1000 ppm affects cognitive performances including decision making and problem resolution. Changes in autonomic systems due to low-level exposure to CO₂ may involve these effects. Further research on the long-term effects of low-level CO₂ exposure on the autonomic system is required. Numerous epidemiological studies indicate an association between low-level exposure to CO₂ beginning at 700 ppm and building-related symptoms. Respiratory symptoms have been indicated in children exposed to indoor CO₂ concentrations higher than 1000 ppm. However, other indoor comorbid pollutants are possibly involved in such effects. In the context of significant linear increase of globally ambient CO₂ concentration caused by anthropogenic activities and sources, reducing indoor CO₂ levels by ventilation with ambient air represents an increase in energy consumption in an air-conditioned building. For the efficient energy control of CO₂ intruding a building from ambient air, the rise of atmospheric CO₂ concentration needs to be urgently suppressed.