Trends in Pollution (IMAGE) Washington University in St. Louis Caption Calculated trends in geophysical PM2.5 values from 1998-2018. Warm colors indicate positive trends, cool colors indicate negative trends and the opacity of the colors indicates the statistical significance of the trends. Credit Martin Lab Usage Restrictions Use allowed with attribution 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.