Filter comparison (IMAGE) University of Technology Sydney Caption The filter on the left contains grey dust from regular urban conditions, the filter on the right contains brown dust from the fires, and the centre picture shows a clean, unused filter. Credit Photo: Raissa Gill / UTS Usage Restrictions Credit must be given to the creator. Only noncommercial uses of the work are permitted. No derivatives or adaptations of the work are permitted. License CC BY-NC-ND 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.