(IMAGE) Goethe University Frankfurt Caption Air pollutants form the condensation nuclei for ice clouds or cirrus clouds (here: Cirrus spissatus). When ammonia, nitric acid and sulfuric acid are present together, they form such condensation nuclei particularly effectively. Credit Joachim Curtius, Goethe-University Frankfurt, Germany Usage Restrictions To be used only when reporting about Goethe University Frankfurt. Indicate credit. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.