The water pulses increase in the first 8 pulses, both in the peak height (Figure ) and in the integrated intensity (see inset in Figure ). The latter reaches a maximum intensity of 3•10 16 molecules gcat -1 per pulse, and then steadily decrease over the rest of the subsequence to 1.6•10 16 molecules gcat -1 per pulse. A similar decay of about 45% is also observed in the peak heights. As already mentioned in section 3.1, the water signal is strongly broadened and therefore the integrated signal intensity of a pulse contains a significant contribution from the preceding pulses and in turn contributes to the following ones. This will shift intensity from the first few pulses into subsequent pulses, but after a few pulses these contributions will cancel out and can be neglected. Nevertheless, this may be responsible for the slight shift to later pulses in the position of the maximum as compared to CH4 pulses. Also here, the general trend is repeated in the second and third subsequence at a slightly lower level of the pulses. From the first maximum to the end of the sequence the water signal decreases by about 60% to 1.2•10 16 molecules gcat -1 per pulse, with the main decay occurring in the first subsequence.