Though the stratospheric ozone is beneficial, ozone at ground level is a harmful air pollutant. Ground-level ozone, formed by the reaction of sunlight with pollutants such as nitrogen oxides and volatile organic compounds, is a major component of smog. It can cause respiratory problems, aggravate asthma, and reduce lung function. Thus, while the ozone layer is crucial for blocking UV radiation, ozone at the ground level poses a toxicological threat to human health.
