GB/T 9780-2013 "Test Method for Dirt Resistance of Coatings of Architectural Coatings" specifies the test principle, procedures, and evaluation methods for the dirt resistance of coatings of architectural coatings, and is applicable to the detection of relevant properties of various types of architectural coatings. The test involves contaminating coating specimens with a standard pollution source, controlling test conditions using a dirt resistance testing instrument for coatings, and measuring the change in reflectance of the specimens before and after contamination using a reflectometer. The dirt resistance performance is quantified by the contamination rate, providing a scientific basis for the quality assessment of architectural coatings.