1.   Another strategy is to control temperatures in the atmosphere, where those two gases mix and create unhealthy ozone gases.

2.   As an alternative, some cities are switching to a form of water treatment called ozonation, which uses ozone gas to kill microorganisms.

3.   Ozone gas is generated by vehicles and agricultural equipment.

4.   Thomas Bonaquisti, director of water quality, looks up at large tanks where ozone gas - a powerful water disinfectant - is created by sparking electricity through oxygen.

5.   This treatment uses ozone gas, a powerful disinfectant created by sparking electricity through oxygen, to kill cryptosporidium and other parasites.

6.   Ozone gas in the stratosphere plays a key role in shielding people, animals and plants from dangerous forms of ultraviolet radiation.

7.   Summertime smog results from a build-up of ozone gas at ground level.

8.   Manufacturers and the oil industry have criticized the action on invisible ozone gas, which forms in the lower atmosphere when sunlight reacts with chemicals from factories and cars.

9.   The combination of heat and accumulation of ozone gas, which causes eye and respiratory problems, has triggered pollution alerts especially in Florence, Bologna and Milan.