a diffuse plasma jet was realized by expanding the preexisting argon filamentary discharge into a diffuse one at atmospheric pressure. examination of emission spectra from the plasma jet shows that the emission intensities of oh and ar increase with the argon flow near the quartz tube nozzle, while the n-2 emission intensity first increases, then decreases, and finally approximately remains unchanged with the increase in the argon flow of interest. it is also found that with the argon flow set at 0.4 l/min,most of the reactive species are gathered close to the nozzle, the oh and ar emission intensities decrease quickly after the plasma propagates out of the nozzle, but the n-2 emission is able to propagate over a larger distance. these distinct spectral emission features of oh, n-2, and ar are attributed to the different generation and quenching mechanisms of their corresponding excited states, i.e., oh(a (2)sigma(+)), n-2(c (3)pi(mu)), and ar(4p)/ar(4s) in the argon plasma jet. additionally, the formation of the diffuse plasma jet has been clarified by observing the discharge burning phase and solving the poisson equation for the electric field distribution in an argon cylindrical dielectric-barrier discharge. the filamentary discharge deposits charged particles onto the dielectric. the positive surface charges in the positive half cycle induce a relatively high field in the local region close to the dielectric. the relatively high field and the high pre-ionization in this local region play a key role in initiating the diffuse positive corona. published by aip publishing.