Guidelines & Tools Probe and Monitoring Path Siting Criteria for Ambient Air Quality Monitoring (40 CFR Appendix E to Part 58 - Appendix E) Share SHARE Facebook share Twitter LinkedIn Copy URL Email Download Download appendix-E_to_part_58 en Added on: 20 May, 2025 Breadcrumb Home Resource Library Probe and Monitoring Path Siting Criteria For Ambient Air Quality Monitoring (40 CFR Appendix E To Part 58 - Appendix E) This appendix to the United States Clean Air Act contains specific location criteria applicable to ambient air quality monitoring probes, inlets, and optical paths of SLAMS, NCore, PAMS, and other monitor types whose data are intended to be used to determine compliance with the NAAQS. These specific location criteria are relevant after the general location has been selected based on the monitoring objectives and spatial scale of representation discussed in appendix D to this part. Monitor probe material and sample residence time requirements are also included in this appendix. Adherence to these siting criteria is necessary to ensure the uniform collection of compatible and comparable air quality data.