The decrease in indoor air quality in enclosed homes is primarily due to which factor?

The correct answer is based on the significant role that fresh air plays in maintaining indoor air quality. In enclosed homes, the lack of sufficient airflow can lead to the accumulation of indoor pollutants such as dust, volatile organic compounds (VOCs), and other contaminants. This is particularly concerning in modern homes, which are often designed to be more energy-efficient and airtight.

When fresh air circulation is reduced, the ability for indoor spaces to "breathe" is compromised, causing higher concentrations of pollutants. Fresh air is crucial for diluting these harmful substances, and its absence can lead to various health issues for residents.

While excessive humidity and electronic usage can contribute to indoor air quality problems, they are not the primary factors affecting the airflow itself. Low occupant density typically would not lead to a decrease in air quality, as fewer people can result in lower levels of indoor pollutants when adequate ventilation is present. Therefore, the reduction in fresh airflow directly correlates with a decline in indoor air quality, making it the most relevant factor in this context.