The European Commission’s science and knowledge service, the Joint Research Centre (JRC) has evaluated sources of air pollutants in the Danube macro-region, a necessary step for the design of action plans to improve air quality. The related study showed residential heating contributed up to 35 percent of PM2.5 pollution in the main cities in the Danube macro-region, followed by agriculture (up to 32 percent), energy production and industry (up to 30 percent) and transport (up to 25 percent).