It is important to indicate air quality level in metropolitan areas as it is harmful to public health. Air quality index (AQI) is a useful tool to convert air quality pollutants concentrations into a single number representing air quality level. There are many air quality index models in the literature to represent air quality level. Two models were selected to assess air quality in Mosul city. The first model utilize the highest sub-index depending on USEPA pollutants standards. The second model includes the weights of all pollutants in the model as an aggregated air quality index (AAQI) model. Air quality concentrations were collected using a fixed monitoring station located in the courtyard of the public library for a year. The results illustrate that the values of aggregated Air quality index model were higher than those of the USEPA model. Air quality category "Moderate" was dominant in winter and spring for the two models. While the category "Unhealthy for sensitive group" was dominant in summer and autumn. Furthermore, the category "Unhealthy" appeared only with aggregated model in autumn. The contribution of air pollutants in AQI can be ranked as PM10, SO2, NO2, CO and O3 from higher to lower. The study concluded that the AAQI is comprehensive and more workable in environmental management.