New indicators for monitoring photosmog

Croatian researchers have developed new indicators that can be used to analyse
photochemical pollution and smog caused by ozone. The indicators are based on simple mathematical formulae and could make it easier for those who monitor pollution levels to make meaningful comparisons between different sites.

Ozone is the main cause of photochemical pollution and smog – pollution that is enhanced by sunlight and is thus at its worst in hot summer months. In humans, photochemical pollution can exacerbate existing health problems, including respiratory and heart disease. Episodes of photosmog have been associated with increased hospitalisations and deaths. The effects also extend to plants, resulting in lower crop yields.

European ozone levels have been measured comprehensively since 19971 and principles for reducing harmful effects of ozone on humans, including alert thresholds, are established under the EU Directive 2002/3/EC2.

Currently, however, no simple indicators exist for comparing air quality between different locations. Therefore, the researchers used a trial and error approach to evaluate various methods of calculating indicator values, eventually deciding on two new indicators that could be used in pollution monitoring.

They developed their indicators based on monitoring data from 12 stations across the EMEP European-wide air pollution monitoring network3. Because pollution levels depend very much on the time of day – they are highest in the early afternoon and lowest in the morning and evening – methods had to be developed that would take these variations into account. Therefore, they chose to incorporate a ratio of maximum-to-minimum daily pollution level into each indicator.

In the first indicator, the maximum-to-minimum ratio was combined with the average daily maximum relative to the average value for the season. The second indicator instead incorporates factors that show how often air quality limits are exceeded, making it more useful for understanding when impacts on human can be expected. This indicator often gives values above 100 and results in clear pollution level classifications. Below 10 is “clean”, 10-40 is “medium” and above 100 is considered polluted.

The researchers say their indicators are useful in two ways. First, they are useful for indicating expected levels of pollutants at particular sites and in the surroundings areas. Secondly, they enable quick comparisons between different sites. However, they stress that indicators are just that – only “indicators” of what is going on at a specific site and are not to be used without careful interpretation and further examination of all the data available.

Science for Environment Policy 08-07-2010
http://ec.europa.eu/environment/integration/research/newsalert/pdf/203na6.pdf