ASTM G222-21 PDF

SIGNIFICANCE AND USE 5.1 Products exposed outdoors degrade due to primarily three stress factors: sunlight, temperature and moisture. The rate of property change is a function of time and stressors’ intensity. 5.2 Whereas the UV irradiance calculated in this practice is independent of material, it is especially relevant to polymeric materials exposed outdoors as the combined action of UV radiation and oxygen is often the dominant factor leading to their degradation. Therefore, estimating UV irradiance is an important parameter to assess the service life of products. 5.3 UV radiant dosage is often more important to determine in the correlation with the amount of degradation than total solar radiant dosage or duration of time. The comparison of UV radiant dosage from one location to another may be used to normalize degradation results. 5.4 Measured UV irradiance data are scarce compared to total solar irradiance data. Many locations that monitor solar resource data only collect data for total solar radiation. This practice allows the user to estimate the amount of UV irradiance from the amount of total solar irradiance for any site. SCOPE 1.1 This practice describes methods to estimate the total solar ultraviolet irradiance on a horizontal surface as a function of Air Mass and geographic location. 1.2 This practice provides a mathematical model for calculating Global Horizontal Ultraviolet irradiance (GHUV) from Global Horizontal Irradiance (GHI) data for a specific location. 1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.