Handheld Mass Monitors are Indoor/Controlled Environment Monitors BUT.....How to 'spot check' ambient air?

Service Bulletin                                                

Aerocet 531, Aerocet 531S, 831 Mass Monitors

Subject: Using a K - Factor                                          13 MAY 2014

The accuracy of the Aerocet 531, 531S, or 831 Mass Monitors depend highly upon the reflectivity of the particulate. The instrument is calibrated in the factory using PSL particles. In many cases, real world particulate can have a completely different characteristic than the calibration aerosol, simply due to the reflectivity properties of the particulate. Coal dust is significantly different in reflectivity characteristic than airborne dust near an aluminum smelter. In many cases, these mass monitors will need a K-factor set into them via the software. This is especially true when the instrument is used outdoors for spot checks.

A K-factor is simply a multiplier. For example, if you have a device that is reading only half of what it should be reading, you normally apply a K-factor of 2 into it. The instrument multiplies the readings by 2, and gives a more accurate comparison.

To set up a K-factor, you need to compare the mass monitor data with a known good reference. This can be any mass monitor accepted as having good data by the reporting agency. For example, a BAM 1020 would be a known good reference since it has USEPA approval and similar approvall in most countries.

The reference must be an instrument that is set side-by-side with the handheld mass monitor. Using data from the nearest AQ station is not close enough. The data on a rooftop on the other side of the city could be very different than what you are monitoring. The instruments should be properly collocated.

Below is an example of a K-factor comparison.

Mass Monitor Data (ug)                               Reference data (ug)

3                                                                        8

6                                                                        9

4                                                                      13

6                                                                      10

5                                                                        8

7                                                                      13       

3                                                                        9

6                                                                      10          

5 (Average)                                                    10 (average)

Of course, you would use more points. The above is an example only.

On our test, the reference is reading twice what the mass monitor is reading. Thus, we would enter a K-factor of 2 into the instrument setup screen through the USB port.

To do this, connect a USB cable between the device and your computer. Open Comet and choose your station. The example below is for the 831.                                                            

Look for the SETUP tab at the top of the terminal window. It will appear as the picture below.

Using the up and down arrows, change the K-factor for each channel as needed. Keep in mind that a K-factor of 0 cannot be used. The K-factor is a direct multiplier. Thus, you would be multiplying your measured value times 0.

Please note: The Aerocet 531, 531S, and 831 Mass Monitors are indoor monitors. However, they can be used outdoors to spot check a site.

For more information regarding K factors or about setting up your Mass Monitor, call or email our service department at service@metone.com or call 541-471-7111 ext. 300.