Tropospheric ozone measurements at the background monitoring stations of Hungarian Meteorological Service

(Zita Ferenczi)

The tropospheric ozone concentration has been monitored in Hungary at four background monitoring stations (K-puszta, Farkasfa, Hortobágy, Nyírjes) by the Hungarian Meteorological Service (HMS). K-puszta is located in the central part of Hungary, on the Hungarian Great Plain (46o58'N, 19o33'E, 125 m asl), relatively far from any human sources. Ozone measurements started in 1990, so there is a long time series of the background concentration of this pollutant.
In 1996 an ozone monitoring network was established with three new places: Farkasfa (46°55', 16°19', 312 m asl) in the western part of Hungary, Hortobágy (47°29', 20°56', 91 m asl) in the eastern part of Hungary and in the Mátra mountain Nyírjes (47°52', 19°57', 702 m asl).
At these stations 10 minutes averaged ozone concentration values are detected continuously.

The ozone monitor
The analyzer uses the principle of ultraviolet absorption; whereby ozone molecules absorb ultraviolet energy at a known wavelength of 254 nm. The UV light available for detection is proportional to the amount of ozone in the sample chamber.
The analyzer determines the ozone concentration in ppb unit with a ten minutes sampling. The range of measured data is in the 0-150 ppb interval. The high ozone concentrations (> 100 ppb) can be detected in summer time and early spring (mainly in March). Concentrations above 120 ppb occur only in rare occasions.

What is tropospheric ozone?
Ozone (O₃) is the primary ingredient of photochemical smog, the type of air pollution that is associated with sunlight-driven chemical reactions. Ozone is formed by a very different process when oxides of nitrogen and reactive organic compounds react together in the presence of sunlight. Motor vehicles are the major contributor of oxides of nitrogen and reactive organic compounds in most cities. Typically, the highest ozone levels are found in suburban locations downwind from the city center, rather than in the city center itself. In some situations plumes with high ozone have been found in locations that are 500 km distant from the apparent emission sources. Ozone episodes in which concentrations rise substantially above background levels occur in summer months when there are long periods of bright sunshine, high temperatures and light winds. The highest ozone concentration can occur when the weather of the Carpathian Basin is controlled by an anticyclone.

Year-to-year variation of ozone concentration measured at the background stations of HMS (1996-2005)

Long term variation of ozone concentration at K-puszta

Ozone concentrations thresholds and exceedences relying upon EC Directive:
The health protection threshold (the highest 8-hour mean within one day > 120 µg/m³) of ozone are exceeded very often at the background stations, especially in summer.
The target value marked out by the EC Directive for the protection of human health is that the health protection threshold is not to be exceeded on more than 25 days per year averaged over 3 years.

The population information threshold (180 µg/m³ for the mean value over one hour) exceedence is usually rare.

Population warning threshold (240 µg/m³ for the mean value over one hour) exceeded at the Hungarian background stations very rarely. In the examined time interval (1999-2005) the ozone concentration level was higher than 240 µg/m³ only in one occasion at K-puszta.