Which criteria pollutant is known for contributing to respiratory issues and is a result of combustion?

Nitrogen Dioxide is recognized as a significant contributor to respiratory problems, particularly because it is a common byproduct of combustion processes. This pollutant is predominantly emitted from vehicles, power plants, and industrial facilities where fossil fuels are burned. When inhaled, nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections, and it is also linked to the development of asthma and other chronic respiratory diseases.

In contrast, while ozone is a concern for air quality and health, particularly at ground level, it is not directly emitted but rather forms in the atmosphere through reactions involving sunlight, volatile organic compounds, and other pollutants, including nitrogen oxides. Carbon dioxide, although related to combustion and a greenhouse gas, is not known to cause respiratory issues directly. Lead, while harmful, is primarily associated with neurotoxic effects rather than respiratory conditions. Therefore, nitrogen dioxide stands out as the pollutant most closely associated with respiratory problems due to its direct link to combustion processes.