Special purpose monitor
Special purpose monitor (SPM) station means a monitor included in an agency's monitoring network that the agency has designated as a special purpose monitor station in its annual monitoring network plan and in the AQS, and which the agency does not count when showing compliance with the minimum requirements of this subpart for the number and siting of monitors of various types. Any SPM operated by an air monitoring agency must be included in the periodic assessments and annual monitoring network plan required by 58.10 and approved by the Regional Administrator.
40 CFR § 58.1
As used in this part, all terms not defined herein have the meaning given them in the Clean Air Act.