The axial profiles of the pulse modulated atmospheric pressure surface-wave argon plasma confined in discharge tubes of different diameters are measured by means of optical emission spectroscopy with respect to the emission intensity, gas temperature, and electron density and temperature. Then, the role of the discharge tube is investigated with respect to its diameter. Furthermore, a simplified theoretical model for high collision frequency is proposed for analysis of the experimental results of electron density obtained by the Stark broadening technique, achieving a good agreement between them for discharge tubes of different diameters.