  We present spatial and temporal distributions of dust on Mars from Ls = 331
in MY26 until Ls = 80 in MY33 retrieved from the measurements taken by the
Planetary Fourier Spectrometer (PFS) aboard Mars Express. In agreement with
previous observations, large dust opacity is observed mostly in the southern
hemisphere spring/summer and particularly over regions of higher terrain and
large topographic variation. We present a comparison with dust opacities
obtained from Thermal Emission Spectrometer (TES) - Mars Global Surveyor (MGS)
measurements. We found good consistency between observations of two instruments
during overlapping interval (Ls = 331 in MY26 until Ls = 77 in MY27). We found
a different behavior of the dust opacity with latitude in the various Martian
years (inter-annual variations). A global dust storm occurred in MY28. We
observe a different spatial distribution, a later occurrence and dissipation of
the dust maximum activity in MY28 than in other Martian years. A possible
precursor signal to the global dust storm in MY 28 is observed at Ls = 200 -
235 especially over west Hellas. Heavy dust loads alter atmospheric
temperatures. Due to the absorption of solar radiation and emission of infrared
radiation to space by dust vertically non-uniformly distributed, a strong
heating of high atmospheric levels (40 - 50 km) and cooling below around 30 km
are observed.
