Tropospheric ozone is formed by the action of sunlight on nitrogen dioxide in the presence of volatile organic compounds (VOCs). Control of ozone concentration relies on controlling emissions of these ozone precursors, with emphasis on nitrogen oxides (NOx) or VOCs (or both) depending on their relative importance, i.e. whether ozone production is NOx or VOC limited. Globally, VOC emissions are dominated by biogenic sources, with limited options for control, unlike the anthropogenic sources for which (at least in Europe and North America) controls have been implemented.
Controls on ozone are necessary because of its effects on both human and ecosystem health. Emission control strategies in the USA and in the EU have focussed primarily on human health exposure targets. The metrics used to measure exposure differ in detail between the USA and the EU, but the broad strategic objectives are similar. Both strategies require emission controls on ozone precursors: NOx and VOCs. In the EU there are additional exposure targets for vegetation, based on exposure above threshold concentrations, although a more reliable flux-based approach to ozone exposure has been developed under the UNECE LRTAP Convention and has been applied to some crop and tree species and natural vegetation. Effects on human health have been valued at €11.9 billion annually in the EU , while economic losses from the effects of ozone on wheat alone are estimated at €3.2 billion in the EU1 and £80-90 million p.a. in the UK.
Globally, effects on health and crop losses are increasing rapidly with industrialization; losses to 4 staple crops from ozone are estimated as $15-25 billion. In addition, ozone also affects the lifetime of many building materials, with associated economic losses (e.g. £74 million per annum for rubber goods in the UK alone), and is responsible for long-term adverse effects on cultural artefacts, and even indoor air quality.
Over the past two decades, there has been a persistent rise in ‘background’ ozone concentrations in the northern hemisphere, attributed primarily to increasing emissions of ozone precursors in Asia. The long-range transport of both precursors and ozone formed in these areas has been demonstrated through measurements, and it is now recognized that control over chronic exposures to ozone cannot be achieved simply by controlling regional emissions, although improvements in the peak concentrations measured regionally have been achieved by controls on precursor emissions.
A good understanding of ozone formation requires global scale and regional models that can incorporate accurately both changes in weather patterns and changes in emissions (both man-made and natural), so as to be able to predict both chronic and episodic ozone concentrations. Where reliable forecasts can be made, exposure of sensitive individuals can be reduced by changing behaviour (e.g. advising people to stay indoors), and impacts on crop species can be mitigated by identifying more ozone tolerant genotypes. With such great diversity of interests in ozone and its effects it is not surprising that separate research communities have focused on their particular concerns, and as a consequence best practice and innovative approaches are not available across the whole spectrum of interests.
For example, routine monitoring of tropospheric ozone to assess human exposure in the UK is related to legal requirements set by the EU, and so must be strictly quality-controlled with independent auditing of measurements, and traceability to the national (and international) standards for concentration measurements held by the National Physical Laboratory (NPL) in the UK. Recently it has become clear that atmospheric researchers, while operating similar instrumentation in the laboratory and in the field, do not always have easy access to traceable standards, and a working group, set up by NCAS (National Centre for Atmospheric Science) this year, is formulating plans to provide this community with access to quality-assured standards.
The network will contribute to a better sharing of expertise on instrument operation, instrument problems and long-term data management. The need for coordination on the management of and access to data is also clear – although the national monitoring network funded by Defra reports data hourly to the UKAir database (accessible online to everyone ) other measurement data may only be recorded by individual projects. There is currently no freely-available catalogue of metadata listing measurements that are being made. Moreover, both measurement and modelling of tropospheric ozone at a range of spatial and temporal scales, let alone their integration, represent major challenges. Most ozone concentration measurements are made outdoors, but people are exposed in numerous micro-environments, mostly indoors.
There is only limited understanding of the relationship between outdoor and indoor ozone concentrations, and between these and personal exposures. If there is a poor correlation between exposure and outdoor concentrations then epidemiological studies that use the available outdoor data will be biased, and may either fail to identify associations between ozone exposure and health effects or may produce erroneous estimates of risk. In addition to atmospheric scientists, many measurements made by teams interested in vegetation effects in remote areas use integrating passive samplers, yet these data may also be of use to others; conversely expertise from the atmospheric community could be of great help in interpreting and understanding the integrating datasets. One common factor for all research teams is a perceived barrier to progress caused by a lack of appropriate technologies, or even the awareness that appropriate measurement systems may exist in other areas of ozone research.