This is the “Parameter Occurrence Code” used to distinguish different instruments that measure the same parameter at the same site. There is no meaning to the POC (e.g. POC 1 does not indicate the primary monitor). For example, the first monitor established to measure carbon monoxide (CO) at a site could have a POC of 1. If an additional monitor were established at the same site to measure CO, that monitor could have a POC of 2. However, if a new instrument were installed to replace the original instrument used as the first monitor, that would be the same monitor and it would still have a POC of 1.
For criteria pollutants, data from different sampling methods should only be stored under the same POC if the sampling intervals are the same and the methods are reference or equivalent. For sites where duplicate sampling is being conducted by multiple agencies or by one agency with multiple samplers, multiple POCs must be utilized to store all samples.
For non-criteria pollutants, data from multiple sampling methods can be stored under the same POC if the sampling intervals are the same and there is only one sample for the time reported. If multiple open path monitors are reporting data for the same parameter, each open path would be assigned a different POC.
While there are no national EPA practices assigning POC values, there may be regional or agency conventions where a POC value may have specific significance. Since these do not apply universally, you will likely get the wrong set of monitors assuming the POC represents something. There is enough metadata avaialable in AQS to correctly classify all monitors (e.g., primary, speciation, etc.)
Numbers do not need to be assigned sequentially.
Must be a number greater than zero (0).
Required on MA transaction (and most other transactions as a key field).
On insert: may not create a monitor with identical state-site-county-parameter-poc values.