  Solar extreme-ultraviolet (EUV) lines emitted by highly charged ions have
been extensively studied to discuss the issue of coronal heating and solar wind
acceleration. Based on observations of the polar corona by the SUMER/SOHO
spectrometer, this paper investigates the relation between the line widths and
kinetic parameters of ions. It is shown that there exists a strongly linear
correlation between two variables $(\sigma/\lambda)^2$ and $M^{-1}$, where
$\sigma$, $\lambda$ and $M$ are the half-width of the observed line profile at
$1/\sqrt{e}$, the wavelength and the ion mass, respectively. The Pearson
product-moment correlation coefficients exceed 0.9. This finding tends to
suggest that the ions from a given height of polar corona have a common
temperature and a common non-thermal velocity in terms of existing equation.
The temperature and non-thermal velocity are obtained by linear least-square
fit. The temperature is around $2.8$ MK at heights of 57$''$ and 102$''$. The
non-thermal velocity is typical 21.6 km s$^{-1}$ at height of 57$''$ and 25.2
km s$^{-1}$ at height of 102$''$.
