What is the normal level of ozone in the atmosphere?

The normal level of ozone in the atmosphere varies with altitude. In the stratosphere, where the ozone layer is located, ozone concentrations typically range from about 200 to 400 parts per billion (ppb). Near the Earth's surface, ozone levels can fluctuate due to pollution and weather conditions, often reaching concentrations of up to 100 ppb during smog events. Overall, the average global concentration of ozone in the atmosphere is around 50-70 ppb.