One of the methods used for sampling formaldehyde is Method 320, which requires a Quality Assurance (QA) spike pursuant to Section 8.6.2 of the method. When proposed in protocols up until now, EMS has been approving the use of acetaldehyde as a surrogate spiking compound for formaldehyde pursuant to Section 3.29 of that method. However, based upon guidance from EPA, we will no longer approve any surrogate spiking when sampling for formaldehyde by FTIR. The QA spike must be formaldehyde. Protocols that have already been approved with acetaldehyde as a surrogate spiking compound for formaldehyde may continue to do so, though we encourage you to voluntarily switch to using formaldehyde for the QA spike and this Listserv should be considered a blanket approval for this switch in your currently approved protocol