Ground based in situ observations of air at Semenic (RO0003R) using chemiluminescence_photolytic, infrared_absorption. These measurements are gathered as a part of the following projects EMEP and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: nitrogen_dioxide in air (mass_concentration_of_nitrogen_dioxide_expressed_as_nitrogen_in_air), carbon_monoxide in air (mass_fraction_of_carbon_monoxide_in_air)