Peter Alpert (IMAGE) Paul Scherrer Institute Caption Peter Aaron Alpert analyses the processes in the finest particles in the air. Harmful substances are already formed in the atmosphere, not just in the human body. Credit Paul Scherrer Institute/Markus Fischer Usage Restrictions PSI provides image and/or video material free of charge for media coverage of the content of the above text. Use of this material for other purposes is not permitted. This also includes the transfer of the image and video material into databases as well as sale by third parties. License Licensed 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.