engleski

A frequency analysis evaluation of some ozone monitoring stations

Tropospheric ozone concentrations exhibit a characteristic time variation with pronounced diurnal cycles and seasonal behaviour. The diurnal and seasonal variations are usually well defined. However, some additional oscillations in ozone concentrations can exist, ones that are much smaller in amplitude than 1-year and 1-day cycles. These small amplitude oscillations can be e. g. attributed to anthropogenic influences, specific meteorological and chemical influences on selected monitoring station and periodic maintenance of the instruments. That is, the spectral analysis of photochemical pollution data can point up hidden conditions that influence particular monitoring stations. Such an analysis, by Fourier transformation (FT) was applied to long-term data from 3 US and 14 European ozone monitoring stations. As expected, strong frequency signals are found for the 1-year and 1-day periods. However, several frequencies of lower signal intensity were observed and could be attributed to anthropogenic activities. A principal component analysis (PCA) was applied to the transformed data sets in order to find these other significant frequencies. Among others, the 7 and 3.5-day frequencies can be considered as markers of anthropogenic influences.

Frequency analysis; long term ozone data; Baton Rouge

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