a, Ice grain spectrum showing the HMOC event with the strongest extended mass range signal of the dataset. The dashed line at 6.4 μs divides the spectrum into the high-resolution part (10 ns sampling) and the low-resolution part (100 ns sampling) (see Methods, ‘Short description of CDA’s chemical analyser subsystem’). There are several relatively narrow peaks between 250 u and 500 u and two much more extended features peaking at about 1,000 u and 1,800 u. In this case, the cations with mass in excess of 200 u are more than twice as abundant (defined by the area under the curve) as those below 200 u. We note the logarithmically scaled TOF axis in this case. These features are usually less frequent and less pronounced than in the extreme case shown here. The extended spectrum frequently shows an instrument-artefact peak at 6.8 µs, which was not considered in our analysis. b, Histogram showing the frequency of occurrences of the features observed in the extended mass range. The definition, and thus significance, of peaks in the extended spectrum is generally lower than in the nominal spectrum. In particular, features above 500 u are sometimes ambiguous and their interpretation should be taken with great caution. However, the statistics shows three preferred mass regions: 200 u–500 u with decreasing frequency, around 1,000 u and around 1,700 u. Even if no sizeable peaks are present, the cation signal in the HMOC spectra is generally higher than the noise level when the low-resolution recording starts and typically only decays to noise level at around 500 u or later.