Final answer:
Ground-level ozone is harmful because it acts as an oxidant and a greenhouse gas, contributing to respiratory health issues, damage to ecosystems, and climate change.
Step-by-step explanation:
Too much ozone in the lower atmosphere is harmful to organisms and ecosystems because it is an oxidant (a) and a greenhouse gas (b). Ground-level ozone, also known as 'bad ozone', forms near the ground when sunlight reacts with pollutants such as nitrogen oxides and volatile organic compounds from vehicles and industrial sources. This ground-level ozone is not only a potent greenhouse gas that contributes to climate change but also a significant air pollutant that can cause respiratory health problems, damage crops, ecosystems, and is the main ingredient in 'smog'.