Air pollution ina metropolitan city like Hong Kong is a major obstacle to improve air quality and living environmentdue to the high population density and the vehicle emission increases.The high air pollutant levels impose harm tothe human health and impair the city image.The characteristic analysis of air pollutants is very important andnecessary to pollutant monitoring, forecasting and controlling.In this study, the interaction patterns of principle airpollutants, e.g. nitrogen dioxide (NO2), nitric oxide (NO), nitric oxides (NOx) and ozone (O3), a secondary pollutant,are investigated based on the measured database in four selected areas, which covers two urban types (i.e. residentialarea, mixed residentialycommercialyindustrial area) in Hong Kong, during the period of 1999–2001.The studyinvolves analyzing the chemical and physical properties, the characteristics of air pollutants and the factors affectingsuch interactions using statistical method.The results reveal several routines in urban air pollutants’ variations,interaction and trends from macro aspect.