Ozone (O3)

Sources of O3 (Ozone)

Ozone is a naturally occurring gas and most commonly found in the stratosphere,  providing an essential process which shields us from the sun’s radiation. Ozone at ground level, however, (referred to commonly as ground-level ozone)  is considered a harmful air pollutant.

O3 has no distinct emission source; instead, it forms at ground level as a secondary pollutant, via photochemical reactions involving NOx, VOCs and methane in a timeframe of hours to days.

Ozone production may peak on hot sunny days in urban environments, as this increases the rate of photochemical reactions of these precursor pollutants. Because of this, O3 experiences seasonal variations in emissions, with summer having higher emission rates.

O3 is a key component of smog formation and can react with other pollutants to exacerbate smog. These reactions are reversible and are a large reason why O3 levels tend to be high in rural areas compared to cities. This is because NO (1 of the 2 compounds of NOx) is very common in cities but much less common in rural areas. The presence of NO increases the rate of Ozone degradation. NO can be seen as mopping up O3 before it can travel away from an urban area. NO2 is more dominant in rural areas, and NO2 reduces the rate of Ozone degradation, thus leading to more O3 in rural areas. This interdependence on precursor pollutants makes assessing and monitoring levels of Ozone difficult.

Ozone, once formed, can travel long distances far from the source, potentially across international borders following a downwind trajectory.

Ozone can be used indoors as an effective odour remover. It's a brilliant oxidiser, enabling it to break down most volatile organic compounds (VOCs). This process is incredibly dangerous if the room is not ventilated afterwards, and may not ever be appropriate within a room which may contain vulnerable people. The process may be more applicable to environments such as garages. 

 

Typical Sources of O3

• Urban Areas With Precursor Pollutants (NOx, VOCs)
• Earth's Stratosphere
• Rural Areas with a greater proportion of NO compared to NO2
• Car Exhausts, Industrial Areas. Chemical Plants

Impacts of O3 (Ozone)

Ozone can immediately inflame and irritate the respiratory tract and lungs. Leading to coughing and chest discomfort. It can irritate the ENT systems as well as cause or exacerbate asthma attacks. O3 chemically reacts with lung tissue (being a powerful oxidant) to increase the likelihood of respiratory infections and pulmonary inflammation. Long-term exposure (8 Hours+) is associated with metabolic disorders, nervous system issues, fertility and foetal development issues and a large increase in respiratory and cardiovascular mortality. Those with respiratory conditions such as asthma or COPD are especially vulnerable to O3 exposure, as are vulnerable individuals such as the elderly, infants, obese individuals and pregnant individuals. 

Common Impacts of O3

• Inflames and irritates the Respiratory Tract and Lungs
• Brain Damage With Prolonged Abuse/Exposure
• Reduced Cognition
• Spatial And Temporal Disorientation

Testing for O3

Ozone can be monitored through passive sampling. A fluorinated ethylene tube contains absorbent, taking 2-4 weeks to complete. 

• Passive Sampling
  

 

The Air Quality Standards Regulations (2010) set ground-level Ozone concentration at no more than 120 µg/m3 over an 8-hour mean. DEFRA defines levels greater than 100 µg/m3 over an 8-hour mean as a ‘moderate’ level of air pollution, where vulnerable individuals may feel negative effects on health. EH40/2005 sets the WEL at 200 µg/m3 over a 15-minute period. 

• Air Quality Standards Regulations (2010); 120 µg/m3 limit over an 8-hour mean
• DEFRA defines anything above 100 µg/m3 as a moderate level of air
• The EH40/2005 limit is 400 µg/m3 over 15 minutes