Air quality data from a one year study at an urban roadside location in Central London are reported for a large number of both organic and inorganic air pollutants. The location is 5 m from the kerbside of a moderately busy road, Exhibition Road, enclosed on each side by buildings. The pollutants measured included NO, NO2, O3, SO2, CO and CO2. together with 28 non-methane hydrocarbons, including measurements of the air toxics: benzene and 1,3-butadiene. The interpretation of the air quality data used simple statistical techniques, including principal components analysis, and air pollution models of the Gaussian plume and box model variety. A comprehensive validation of the published emission inventory estimates for London was attempted using the observed air quality data. Separate contributions from the local traffic on Exhibition Road, from the general traffic in Central London, natural gas leakage and fuel combustion have been identified. The agreement between the emission factors required to explain the observed concentrations and those in the literature was excellent for a number of air pollutants and these should be of value in environmental impact assessments. Attention was also directed to an intense wintertime pollution episode which occurred during the study period, when the concentrations of all pollutants were considerably higher than usual. Elevated nitrogen dioxide concentrations were a significant feature of this episode and the box model was used to ascertain its likely production mechanism. A relationship between the hourly mean nitrogen dioxide and NOx concentrations was defined which should have general applicability in air quality policy assessments.