Which of the following pollutants is regulated under NAAQS?

To understand why the correct answer encompasses all of the listed pollutants, it's important to clarify what the National Ambient Air Quality Standards (NAAQS) are. NAAQS are established by the Environmental Protection Agency (EPA) under the Clean Air Act to protect public health and the environment from the harmful effects of certain pollutants.

Lead and ozone are both specifically regulated under NAAQS due to their significant health impacts. Lead particulates have been found to cause a range of health issues, particularly in children, where exposure can lead to developmental problems. Ozone, particularly at ground level, can cause respiratory issues and other health problems, especially among vulnerable populations.

While carbon dioxide is not currently regulated under NAAQS in the same way that lead and ozone are, it is recognized as a greenhouse gas contributing to climate change. However, its regulation primarily falls under different legal frameworks, rather than NAAQS established for criteria pollutants, which focus on substances that directly affect air quality in the environment.

Given this context, the phrasing of the question and the understanding of how these pollutants are classified under air quality regulations leads to the conclusion that whilst all options provided (including carbon dioxide, where regulation is evolving) are significant environmental concerns, only lead and ozone are