e-Digest Statistics about: Air Quality
Concentrations of Ground level ozone (O3)
Ozone (O3)can affect human health and can damage plants and crops [35], [16]. Exposure to ozone may cause irritation to the eyes and nose and very high levels can cause damage to the airway lining.
At ground level, ozone occurs naturally but levels can be increased as a result of the presence of other pollutants. As a secondary pollutant, it is formed by a series of reactions between nitrogen dioxides (NOx), volatile organic compounds (VOCs) and oxygen in the presence of sunlight. There is evidence that near ground level ozone concentrations of typically 20 to 30 µg/m3 per annum have doubled over the past 100 years to current levels of approximately 70 µg/m3 per annum over the UK. Production of ozone is affected by the weather, which can also lead to ozone and the pollutants that cause it being blown over from mainland Europe. Ozone episodes in which concentrations rise substantially above background levels occur in the summer months when there are long hours of bright sunlight, temperatures above 20°C, and light, or no, winds. Once formed, ozone can persist for several days and can be transported long distances.
Table 15 shows concentrations and exceedances of ozone against Air Quality Strategy, UK and EC criteria at automatic monitoring sites in 2006. The objective that the daily maximum of running 8 hour means should not exceed 100 µg/m³ more than 10 times a year by the end of 2005 was met by 14 per cent of sites in 2006. During 2006, all monitoring sites which met data capture targets, except London Marylebone Road recorded some 'moderate' hourly mean ozone levels . 'High' levels were recorded at 46 sites out of 60 (meeting data capture requirements) but no 'very high' levels were recorded. Table 15 shows that 85 of the 91 monitored sites had some exceedances of the guideline standard in 2006. Real time pollution data and forecasts for ozone and other pollutants can be accessed from the air quality archive.
Figure 11 and Figure 12 show trends in exceedances of the objective level for the daily maximum 8 hour running mean at urban and rural sites. Ozone concentrations recorded at urban sites are generally lower than those at rural sites because ozone can be destroyed by reaction with nitric oxide to form nitrogen dioxide, and urban areas tend to have higher levels of nitric oxide than rural areas.
Damage to vegetation caused by ozone may take several forms, depending on the concentrations to which plants are exposed. At high concentrations, brown or white flecking often appears on leaves. At lower concentrations, plant growth may be reduced without any visible damage. The EC Directive sets vegetation guidelines for ozone concentrations, in terms of the sum of the differences between hourly concentrations greater than 80 µg m-3 and 80 µg m-3 during May-July between 8am and 8pm. Table 15 shows that only 2 sites out of 85 did not exceeded the daily mean level in 2003, Reading, which closed in February 2003, and Bury Roadside. Twenty-seven sites recorded exceedances of the hourly mean level.
[1] Excludes 4 sites where monitoring did not take place during the summer months.
Data Tables:
- References, further reading and links to other resources:
- [16] Defra, National Emission Ceilings Directive: National Strategy to Combat Acidification, Eutrophication and Ground-level Ozone
- [35] Department of the Environment, (1997). Ozone in the United Kingdom 1993: the Fourth Report of the UK Photochemical Oxidants Review Group.
- Internet Links:
- UK National Atmospheric Emissions Inventory (NAEI)
- National Air Quality Information Archive
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Page last modified: 9 August 2007
Page published: 30 September 2005