GB/T 12085.20-2022, "Optics and photonics - Environmental test methods - Part 20: Humid air containing sulfur dioxide or hydrogen sulfide," is a national recommended standard that officially came into effect on May 1, 2023. It is used to assess the tolerance of products in corrosive and humid environments, such as those affected by industrial pollution. This standard specifies a unified method for testing optical and photonic instruments and related components in humid air containing sulfur dioxide or hydrogen sulfide, to evaluate the corrosion resistance of their metal parts, coatings, and other materials, as well as the overall stability of their performance. The core testing instrument for conducting this test is a controlled atmosphere environmental test chamber, which must be capable of precisely simulating and maintaining the specific temperature, humidity, and concentration conditions of corrosive gases (SO₂ or H₂S) required by the standard. The standard includes clear technical specifications for the purity of test gases, sample pretreatment (such as preheating to prevent condensation), spacing between samples, and the proportion of sample volume in the test chamber (not exceeding 50%), to ensure the consistency and reliability of test results.