Monitoring atmospheric composition & climate
Nice weather brings elevated surface ozone values

The current flow of very warm air from southern Europe into middle and North-Western Europe does not only bring high temperatures. The nice sunny weather also causes adverse air quality episodes, which can affect health. MACC-II European air quality forecasts for today and tomorrow show clearly increased surface concentrations of ozone, especially marked over the Benelux but also over large parts of central Europe as shown in the image.


Please click on image to see animation.

Elevated surface ozone concentrations are formed through a combination of two main factors. Firstly, high levels of solar radiation are needed to provide the energy needed for the chemical reactions forming ozone to take place. The warm sunny weather during the next two days provides plenty of this solar energy. Secondly, increased levels of precursors of ozone, nitrogen dioxide (NO2) and Volatile Organic Compounds (VOC) are needed to fuel the chemical reactions and build up large concentrations of ozone. NO2 originates mainly from anthropogenic activities (cars, industries…), while VOCs are emitted by plants as well as anthropogenic sources. The MACC-II European air quality forecasts show that these needed components are all in place today and tomorrow to form ozone levels that are likely to exceed regulatory thresholds in some places. Both temperature and surface ozone therefore follow very similar temporal patterns over the next few days, as illustrated by the animation.


The long-term objective of the 2002 European Directive on ambient air ozone is to limit the number of days with 8-hour average of ozone above 120 μg.m-3 to less than 25. This Directive also requires national authorities to inform the public about incidence of ozone concentrations in excess of 180 μg.m-3 in hourly average, the alert threshold being defined at 240 μg.m-3. The maps below show the daily surface ozone maximum as forecasted by MACC-II for the next few days. It provides an indication where the thresholds might be exceeded; please refer to local and national authorities for more precise information. In-situ observations are used a posteriori to validate the MACC-II forecasts.


Surface ozone daily peak (μg.m-3)


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