This activity is for identifying an appropriate site for deploying a MiniVol sampler for Particulate Matter monitoring.
Monitoring Site Identification
These instructions follow Airmetrics requirements and conform to US Code of Federal Regulations (40 CFR part 58, Appendix E, Section 8: PM10 & 2.5) for micro scale monitoring. NOTE: the MiniVol is not a Federal Reference Method.
The Minivol can be mounted to any 5cm (2") diameter or smaller pipe with the U brackets, or larger posts using the ratchet straps.
The MiniVol should be positioned so that there is a 270° arc of unrestricted airflow around it and no significant obstruction along the path to the source in question (or site of concern) along the predominant seasonal wind direction. This requirement doesn't apply if source to be monitored is a street 'canyon.'
The MiniVol should be placed with the air inlet:
- facing upward
- 2-7 meters (6'7" - 23') above ground level
- at least 30cm (12") from any obstacle to air flow.
- at least 2 meters (6'7") from walls and architectural features
- at least 5 meters from natural gas combustion flues
- away from fuel oil, coal, or solid waste incineration
- at a distance at least twice as far away as the heights of the nearest obstacle that protrudes above the sampler.
- at least 20 meters from the dripline of the nearest tree. If trees are unavoidable, at least 10 meters from the nearest tree with the tree as a noted obstruction in the Field Data Log.
Record photos of your monitoring site and mounting location so that there is a record of the distances to obstacles.
Pick a sampling site name to be used consistently across records.
Recording local weather conditions
In order to accurately measure a precise quantity of air, the local temperature and pressure are needed. Many sources of local weather information are available.
No matter which source you choose, make sure to use the same source every time and record the source in your notes.
Source of weather info:
- NOAA weather station from Weather.gov (enter your zip code)
- a report from the local weather radio
- Weather Underground Personal Weather Station Network
- a weather report on a television or radio station, or the newspaper.
Adjusting for altitude
The local weather source should measure similar conditions to those affecting your monitoring site. If your monitoring site is at a substantially different elevation than your source of weather information, it may be useful to substitute an estimated pressure for the station's measured pressure.
A calculator implementing the following equation is available in the MiniVol spreadsheet.
Ambient atmospheric pressure =
Psea x (1- Elevation/145330)5.25
where Elevation is in feet and Psea = atmospheric pressure at sea level (nominally 760mmHg)
(Equation 2 Pressure Correction, MiniVOl TAS Manual section 8.2)
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