Positive ion low-temperature fast atom bombardment mass spectra of the frozen nitric acid-water system with an initial components ratio which provides preferential formation of the crystalline hydrate of the nitric acid trihydrate, HNO(3).3H(2)O, are reported. A complicated spectral pattern is created by a number of cluster sets which, on the basis of discussion, were attributed to (H(2)O)(n). NO(+) (n = 1-3), (H(2)O)(n).NO(2)(+) (n = 1, 2), (HNO(3))(m). (H(2)O)(n).H(+) (m = 1-5 and n variable) and (H(2)O)(n).H(+) (n = 1-9). Similarities between the size-dependent behavior of hydrate clusters of nitrogen oxides and nitric acid obtained with sputtering from the solid in the present low-temperature experiments and under gas-phase conditions (reported earlier in the literature) were revealed. A suggestion as to possibility of the yield of the cluster ions sputtered due to energetic particle collision with the frozen grains of water ice and nitric acid trihydrate, present in the atmosphere, to the total ionic population of the atmosphere is discussed. Copyright 1999 John Wiley & Sons, Ltd.