Indoor air quality standards are designed to protect human health by ensuring that the air inside buildings is safe to breathe. They aim to reduce the risk of respiratory illnesses, improve the overall health and well-being of building occupants, and create a comfortable and productive indoor environment.

In the United States, the Environmental Protection Agency (EPA) is responsible for setting indoor air quality standards. The EPA establishes National Ambient Air Quality Standards (NAAQS) for outdoor air and provides guidance on indoor air quality through its Indoor Air Quality (IAQ) program.

The EPA's indoor air quality standards regulate six major pollutants: carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), lead (Pb), and radon (Rn). These pollutants can cause a range of health problems, including respiratory illnesses, heart disease, cancer, and developmental disorders.

The EPA's indoor air quality standard for carbon monoxide (CO) is 9 ppm (parts per million). This standard is designed to protect human health by reducing the risk of CO poisoning, which can cause headaches, dizziness, nausea, and even death.

Outdoor air pollution is not a common source of indoor air pollution because it is typically filtered out by the building's envelope. However, outdoor air pollution can enter buildings through open windows and doors, or through cracks and gaps in the building's structure.

The recommended ventilation rate for indoor spaces to maintain good air quality is 0.3 to 0.6 air changes per hour (ACH). This means that the entire volume of air in the space should be replaced with fresh air every 0.3 to 0.6 hours.

Opening windows and doors is not a common method for improving indoor air quality because it can allow outdoor air pollution to enter the building. In some cases, opening windows and doors can actually worsen indoor air quality by bringing in more pollutants than it removes.

The primary health risk associated with exposure to radon gas indoors is cancer, particularly lung cancer. Radon is a radioactive gas that can enter buildings through cracks and gaps in the foundation or through the water supply. It is the leading cause of lung cancer among non-smokers.

Skin irritation is not a common symptom of poor indoor air quality. However, some people may experience skin irritation from exposure to certain chemicals or pollutants in the air, such as formaldehyde or cleaning products.

The EPA's indoor air quality standard for formaldehyde is 0.1 ppm (parts per million). This standard is designed to protect human health by reducing the risk of eye, nose, and throat irritation, as well as other health problems associated with exposure to formaldehyde.

Cleaning products are not a common source of formaldehyde indoors. However, some cleaning products may contain formaldehyde, so it is important to read the labels carefully and choose products that are low in or free of formaldehyde.

The EPA's indoor air quality standard for nitrogen dioxide (NO2) is 0.05 ppm (parts per million). This standard is designed to protect human health by reducing the risk of respiratory problems, such as asthma and bronchitis, as well as other health problems associated with exposure to NO2.

Tobacco smoke is not a common source of nitrogen dioxide (NO2) indoors. However, tobacco smoke does contain other harmful pollutants, such as carbon monoxide and particulate matter, which can contribute to poor indoor air quality.

The EPA's indoor air quality standard for particulate matter (PM) is 10 μg/m³ (micrograms per cubic meter). This standard is designed to protect human health by reducing the risk of respiratory problems, such as asthma and bronchitis, as well as other health problems associated with exposure to PM.

Cleaning products are not a common source of particulate matter (PM) indoors. However, some cleaning products may contain chemicals that can react with other substances in the air to form PM.