Air pollution is a local, regional and transboundary problem caused by the emission of specific pollutants. Beside the most problematic pollutants particulate matter and ozone, nitrous oxides (NOx) gained more and more importance. The major sources of NOx are high temperature combustion processes (e.g. from car engines and power plants). NOx have widespread environmental and health effects. They contribute to the acidification of soil and surface water and furthermore to the formation of ozone and particulate matter with associated climate effects. Nitrogen dioxide (NO2) can affect the liver and lung and leads to an increased susceptibility to respiratory infection. Since 2010 the limit of the annual mean NO2 concentration is 40 µg m-3. Especially in urban areas car emissions at traffic hotspots lead to more frequent transgression of the NO2 limit values. Therefore the interest in new methods to solve this problem is increasing. A promising idea in addition to reducing the direct emissions of the pollutants is the use of photocatalytic active materials. In order to do this, photocatalysts as titanium dioxide (TiO2) were added to paints or concrete. Under irradiation with light (UV light) these materials are able to degrade the pollutants on its surface. The TROPOS as one partner in the Life+ project PhotoPAQ (Demonstration of PHOTOcatalytic remediation Processes on Air Quality) wants to evaluate the feasibility of using such TiO2 based photocatalytic active material to alleviate the air pollution problem under real atmospheric conditions. Before demonstrating the photocatalytic effect under realistic conditions it is necessary to identify gas phase and particulate compounds (tracers) for the photocatalytic heterogeneous reactions under laboratory conditions. In addition to the lab experiments with established ISO standard reactors, a construction is used, which enables us to investigate the efficiency of the photocatalytic material in our aerosol chamber (Leipziger Aerosolkammer LEAK). Based on these results, the material will finally be tested under real atmospheric conditions in two field campaigns. The data obtained will provide an overview on the behavior of nitrogen oxides and other air pollutants on these surfaces under irradiation with UV light and allow an initial assessment of this material with respect to the goal of "improving urban air quality."