This action revises the definition of volatile organic compounds (VOCs) under the Clean Air Act (CAA). This revision adds four chemical compounds to the list of compounds excluded from the definition of VOC on the basis that each of these compounds makes a negligible contribution to tropospheric ozone formation. These compounds consist of four hydrofluoropolyethers (HFPEs) which are identified as HCF<INF>2</INF>OCF<INF>2</INF>H (also known as HFE-134), HCF<INF>2</INF>OCF<INF>2</INF>OCF<INF>2</INF>H (also known as HFE- 236cal2), HCF<INF>2</INF>OCF<INF>2</INF>CF<INF>2</INF>OCF<INF>2</INF>H (also known as HFE-338pcc13), and HCF<INF>2</INF>OCF<INF>2</INF>OCF<INF>2</INF>CF<INF>2</INF>OCF<INF>2</INF> H (also known as H-Galden 1040X or H-Galden ZT 130 (or 150 or 180)). If an entity uses or produces any of these four HFPE compounds (these being in the family of products known by the trade name H-Galden) and is subject to the EPA regulations limiting the use of VOC in a product, limiting the VOC emissions from a facility, or otherwise controlling the use of VOC for purposes related to attaining the ozone national ambient air quality standards (NAAQS), then the compound will not be counted as a VOC in determining whether these regulatory obligations have been met. This action may also affect whether any of these compounds is considered a VOC for state regulatory purposes, depending on whether the state relies on the EPA's definition of VOC. In addition, the EPA is making certain technical corrections to the current list of exempt compounds.