PhD Thesis, 2010 - University College Cork

Distinguishing peaks from background emission of nitrous oxide
Unfortunately, we were not able to conduct such a test due to relatively low accuracy
of the management data.
4.5.2. Peak event
The notion of an emission/uptake event implies long and continuous peak flux,
extending for days or even weeks. However, this understanding was developed
primarily for the daily-averaged flux time series. In our analysis of half-hourly time
series we did not observe events of such long duration (see Validation subsection for
details regarding daily series analysis). Figure 4.4 presents a few examples of emission
and uptake events that we were able to identify. Typically, an emission or uptake event
appears to have an almost bell-curve shape with rising and falling limbs, in terms of
absolute values. It can be seen, that overall a bell shape curve of the event extends
beyond immediately adjacent periods, i.e., there is a visible trend among close peak
periods that are separated by non-peak periods. The explanation for this variation may
lie in the variability of the wind direction that might transport low flux from nonemitting
fields to the sensor. When breaks and shape are taken into account, sustained
events with durations up to 18 hours can be identified. The duration of uptake events is
shorter on average and does not exceed 6.5 hours.
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