What is air pollution defined as?

Air pollution is defined as a harmful substance built up in the air to unhealthy levels. This definition emphasizes the presence of pollutants that can be detrimental to human health and the environment. Air pollutants can include a variety of substances such as particulate matter, carbon monoxide, sulfur dioxide, nitrogen oxides, and volatile organic compounds. When these substances are present in the atmosphere in amounts that exceed established safety thresholds, they can cause respiratory problems, cardiovascular diseases, and contribute to climate change.

Understanding air pollution in this context is crucial because it highlights the significance of monitoring air quality, implementing regulations to limit emissions from industries and vehicles, and taking steps to reduce pollutants to safeguard public health and the ecosystem. The other options, while related to environmental issues, pertain to different types of pollution (sound, light, and water), and thus do not capture the specific definition of air pollution.