Although the atmosphere includes a layer of ozone, ground-level ozone is harmful. Not only does it add to global warming, ground-level ozone is detrimental to human health by causing or worsening respiratory problems. In addition, it negatively impacts ecosystems by damaging vegetation. Each year, ozone causes $500 million worth of reduced crops, according to the U.S. Environmental Protection Agency. Factories involved with industrial processes, like manufacturing metals or chemical solvents, contribute to ground-level ozone production. Power plants, vehicle emissions and burning fossil fuels also produce ozone. Although these processes do not directly release ozone, they produce nitrogen and volatile organic chemicals. When these chemicals combine in the presence of sunlight, they form ozone.