Suspended Particulate Matter (SPM) standards can vary by country, but generally, they are defined based on the concentration of particulate matter in the air. In India, for example, the National Ambient Air Quality Standards (NAAQS) specify the following limits for SPM: 24-hour average: 500 µg/m³ Annual average: 60 µg/m³ These limits are established to protect public health and the environment. Different countries may have their own standards, so it's essential to refer to the local regulations for precise values.