Ozone is a gas composed of three atoms of oxygen (O3). Ozone occurs both in the Earth's upper atmosphere and at ground level. Ground level ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. 

Foundries are not significant emitters of NOx  other than NOX emissions from cupolas  and other combustion processes.  However, it is important for the industry be informed about any new developments in ozone regulations as a result of  VOC emissions from some melting and casting operations, especially  where chemically-bonded sand is used for mold- and core-making.

In 2015, the ozone NAAQS was reduced to 0.070 ppm (8-hour average) from 0.075 ppm. . This revised standard is expected to  have a protracted implementation schedule as a result of legislative and/or executive branch actions.  Available information is provided below.