History of Ozone in Timeline

Ozone (O3) is a pale blue, pungent-smelling inorganic molecule and allotrope of oxygen. It's formed when ultraviolet (UV) light or electrical discharges act on dioxygen (O2). Less stable than O2, it breaks down in the lower atmosphere. While present in low concentrations throughout the atmosphere, ozone is most concentrated in the stratospheric ozone layer, where it absorbs the majority of the Sun's harmful ultraviolet radiation. This absorption is crucial for protecting life on Earth from damaging UV rays.

1908: Ozonisation of London Underground introduced

In 1908, artificial ozonisation of the Central Line of the London Underground was introduced for aerial disinfection.

1910: OSHA permissible exposure limit for ozone established

The U.S. Occupational Safety and Health Administration has established a permissible exposure limit (PEL) of 0.1 μmol/mol for ozone, calculated as an 8-hour time weighted average, as defined by 29 CFR 1910.1000 table Z-1.

1911: Harmful effects of ozone inhalation

In 1911, Leonard Hill and Martin Flack published findings in the Proceedings of the Royal Society B, stating that the belief in ozone's healthful effects was unfounded. They found that the only well-established effect of ozone was that it caused irritation and edema of the lungs, and death if inhaled in relatively strong concentration for any time.

1923: Georg-Maria Schwab refutes the oxozone hypothesis

In 1923, Georg-Maria Schwab successfully solidified ozone and performed accurate analysis which conclusively refuted the oxozone hypothesis. This was part of his doctoral thesis under Ernst Hermann Riesenfeld.

1955: Tropospheric ozone effects

Starting in 1955 and continuing to 2000, tropospheric ozone was shown to be responsible for approximately 30% of upper Southern Ocean interior warming.

1956: Ozonisation of London Underground phased out

By 1956, artificial ozonisation of the Central Line of the London Underground was phased out. However the beneficial effect was maintained by the ozone created incidentally from the electrical discharges of the train motors.

1987: Montreal Protocol established

In 1987, the Montreal Protocol was established. This led to a ban on the production of many ozone-depleting chemicals due to concerns over the health effects of ozone decline in the stratosphere.

1997: 8-hour ozone standard

In 2004, the EPA allotted the Denver Metro/North Front Range as non-attainment areas per 1997's 8-hour ozone standard, but later deferred this status until 2007. The non-attainment standard indicates that an area does not meet the EPA's air quality standards.

2000: Tropospheric ozone effects

Starting in 1955 and continuing to 2000, tropospheric ozone was shown to be responsible for approximately 30% of upper Southern Ocean interior warming.

2003: Ozone and heat effects during European heat waves

In 2003, an investigation assessing the joint mortality effects of ozone and heat during the European heat waves concluded that these effects appear to be additive.

2004: Denver Metro/North Front Range area designated as non-attainment

2007: Denver Metro/North Front Range area status deferred

May 2008: EPA lowered ozone standard

In May 2008, under a court order, the EPA lowered its ozone standard from 80 nmol/mol to 75 nmol/mol, although its scientists and advisory board had recommended lowering the standard to 60 nmol/mol.

2008: Colorado Ozone Action Plan created

In 2008, the Colorado Ozone Action Plan was created, which includes plans to evaluate emission controls for large industrial sources of NOx and statewide control requirements for new oil and gas condensate tanks and pneumatic valves.

2008: EU ozone concentration target value

In accordance with Directive 2008/50/EC, the EU's current target value for ozone concentrations is 120 μg/m.

2008: Primary standard set

In the 2008 final rule, the 8-hour primary standard was set at 0.075 μmol/mol.

January 7, 2010: EPA announced proposed revisions to the National Ambient Air Quality Standard (NAAQS)

On January 7, 2010, the U.S. Environmental Protection Agency (EPA) announced proposed revisions to the National Ambient Air Quality Standard (NAAQS) for the pollutant ozone, the principal component of smog.

January 2010: EU ozone concentration target value enforcement begins

Starting January 2010, the EU's target value for ozone concentrations, which is 120 μg/m, should not be exceeded on more than 25 calendar days per year, in accordance with Directive 2008/50/EC.

2011: Regional Haze Plan released

In 2011, the Regional Haze Plan was released, which included a more specific plan to help decrease NOx emissions.

October 26, 2015: EPA published a final rule revising the 8-hour primary NAAQS

On October 26, 2015, the EPA published a final rule revising the 8-hour primary NAAQS from 0.075 ppm to 0.070 ppm, with an effective date of December 28, 2015.

December 28, 2015: EPA rule revision becomes effective

On December 28, 2015, the EPA's final rule revising the 8-hour primary NAAQS from 0.075 ppm to 0.070 ppm became effective.

2021: Ozone generators made available to schools

In the Autumn term 2021, ozone generators were made available to schools and universities in Wales for aerial disinfection of classrooms after COVID-19 outbreaks.

2022: Crop loss due to ozone pollution in East Asia

A 2022 study concludes that East Asia loses 63 billion dollars in crops per year due to ozone pollution, a byproduct of fossil fuel combustion. China loses about one-third of its potential wheat production and one-fourth of its rice production.