Inductively coupled plasmas (ICPs) are used in spectrochemical analyses. The introduction of the sample by means of an aerosol are widely used. The introduction and the total evaporation of the aerosol is required in order to obtain a good repeatability and reproducibility of analyses. To check whether the vaporization of the aerosol droplets inside the plasma is completed, a solution could be used to compare the experimental results of the emission spectral lines with theoretical results. An accurate calculation code to obtain monatomic spectral lines intensities is therefore required, which is the purpose of the present paper. The mixtures of argon, water and nitric acid are widely used in spectrochemical analyses with ICPs. With these mixtures, we calculate the composition, thermodynamic functions and monatomic spectral lines intensities of the plasma at thermodynamic equilibrium and at atmospheric pressure. To obtain a self sufficient paper and also to allow other researchers to compare their results, all required data and a robust accurate algorithm, which is simple and easy to compute, are given.