What role does fresh air play in the indoor environment?

Fresh air plays a crucial role in maintaining a healthy indoor environment by helping to dilute indoor contaminants. When fresh air is introduced into a space, it increases the overall air exchange rate, which effectively lowers the concentration of pollutants that may be present, such as volatile organic compounds (VOCs), allergens, and carbon dioxide. By reducing these contaminants, fresh air contributes to better indoor air quality, leading to a healthier living or working environment.

For example, in a crowded room with limited ventilation, the buildup of carbon dioxide can lead to discomfort and decreased cognitive function. Introducing fresh air helps reduce the concentration of CO2 and other harmful substances, allowing occupants to breathe easier and feel more alert.

The other options describe different aspects of air quality and environmental impacts but do not accurately represent the primary function of fresh air in indoor spaces. While fresh air can help in controlling humidity levels, it does not create a barrier. Additionally, fresh air does not directly eliminate pollutants but rather dilutes their concentration, making them less harmful. Lastly, fresh air exchange can sometimes lead to higher energy costs if not managed properly; however, its benefit in improving air quality typically outweighs any potential negative impacts on energy efficiency.