Ambient Monitoring

with Partector 2 & Partector 2 Pro

Ambient measurements with Partector 2 & Pro

A growing number of customers are using the Partector 2 and Partector 2 Pro for continuous environmental monitoring rather than for shorter handheld exposure or occupational hygiene measurements. Performing such measurements and ensuring high data quality is more complex than making short indoor measurements. There are five main issues to consider:

 Avoid high temperature
 Avoid high humidity (or worse, water)
 Avoid high inlet losses
 Avoid inlet clogging
 Perform continuous quality control

We recommend you follow the best practices described below to avoid producing bad or useless data, or in the worst case, damaging your instrument.

Indoor measurement stations

Using the Partector 2 in a climate-controlled measurement station or container avoids issues with temperature and humidity and is ideal.

Care must still be taken:

 Ensure that the correct tubing is used. Especially, conductive silicone tubing that is frequently seen is not suitable for the Partector 2.

 Long inlet lines may lead to high losses of particles due to diffusion. Read the section on Intercomparing Results.

 The Partector 2 and other aerosol instruments display warnings and errors if something is wrong. Monitor the status of your instruments regularly. For our devices, this is easily done by using our IoT data cloud.

Outdoor ambient monitoring without controlled environment

The Partector 2 is miniature and needs very little power. It can run for a long time (weeks) on an external battery, or be powered with a small solar panel. It can also be mounted anywhere in a small protective enclosure due to its small size, and does not need a full-blown measurement station. This makes it very attractive for ambient measurements in locations which are normally not covered by monitoring networks.
If you want to use the Partector for such measurements, it needs to be protected from high temperatures and humidities. As meteorological conditions may differ widely depending on location, it is impossible to give detailed instructions that will fit every location. However, you can apply the following general principles taking your local meteorological conditions into account.

Device temperature

The Partector 2 should not be operated below 0°C or above 40°C. Temperatures below 0°C will cause problems when charging the battery, reducing its lifetime. Temperatures above 40° will reduce the lifetime of multiple internal components and may cause early device failure.
Depending on your location, the design of the enclosure, and its exposure to sunlight, the temperature range from cold winter nights to sunny summer afternoon temperatures can be huge!

We recommend the following:

 Avoid direct exposure of the enclosure to sunlight as much as possible in particular at the hottest time of day (typically 3-5 PM).
 If you use solar cells to power your setup, they can provide shadow to the enclosure.
 Use a white enclosure to reduce heating by sunlight - the whiter the better. A light white paint finish reduces the temperature inside by up to 10°C!!
 Batteries that might be used with solar cells are also restricted to certain temperature ranges and especially charging below 0°C is not recommended or may be impossible.

Examples of a white enclosure shadowed by solar cells.

Humidity inside the device

For long-term environmental monitoring, the Partector 2 should be operated at relative humidities (RH) below about 60%. The Partector 2 is usually warmer than its surroundings due to waste heat. This reduces the internal RH below that of the outside air, but it may not be enough at high outdoor RH, for example when it is raining. Furthermore, as the sun rises, the air and surroundings heat up very quickly and the absolute humidity rises rapidly, while the Partector heats up more slowly in the shaded protective enclosure. In such situations, the RH in the device might be higher than in the ambient air.
To protect itself against high RH, the Partector 2 will turn on a small heater at more than 80% RH. This heater is not very powerful, and we recommend to add some insulation around the Partector 2 in the enclosure to keep its internal temperature higher relative to ambient. You should aim for about 5° above ambient.
High humidity will not damage the device unless it condenses and water accumulates inside the device. Issues with high humidity will cause warnings, visible on the device display, in the data file, or in the cloud dashboard if the device is connected to the cloud.

Humidity inside the enclosure

The Partector 2 has an air outlet on its side. The enclosure may be cooler than the surrounding air (as explained above, mostly in the early morning), and then condensation might occur in the enclosure. We recommend to create an exhaust flow path to directly remove the sampled air from the enclosure.
Some enclosures are airtight. In this case, you must create an exhaust flow path, as otherwise the sampled air has nowhere to go and the Partector's pump will not be able to maintain the normal sample flowrate.

Inlet protection against insects and water

Make sure that your inlet design will protect against the aspiration of water by the Partector 2. For example, a simple tube oriented toward the ground is a really bad idea, as a water drop can form at its end when it is raining, which will be sucked into the device. The inlet diameter must be large enough that this cannot happen.
Insects crawl everywhere, and like to hide in small holes. A fine mesh can protect the inlet. However, if the mesh is too fine, the inlet may become clogged over time, affecting the measurement results. This is an effect that is difficult or impossible to detect based on the system and measurement data and only regular inspection and cleaning helps.

Losses due to the inlet

Once you have designed an inlet to protect against rain and insects, it will also remove some of the particles that you want to measure. The Partector 2 is calibrated without additional inlet, and any particle losses in the inlet need to be taken into account by the user. In general, try to keep the inlet flow path short to reduce diffusion losses of ultrafine particles.
You may also use an impactor or a cyclone in your inlet system. Under normal conditions, this is not really necessary, but if you are measuring in an environment with many coarse particles, it could be sensible. Cyclones and impactors will add to the inlet losses, and may also clog over time, so make sure to clean your inlet system periodically.


Over time, the insides of the Partector 2 become contaminated with dirt. This is unavoidable since dirt in the air is what is measured. When measuring in dirty environments, protection against coarse dust might increase the time between service intervals. The Partector 2 tracks a lot of internal parameters and will display warnings if the buildup of dirt has become critical.
For more information on maintenance and recalibration, check out our maintenance & calibration recommendations


You can power your Partector 2 either via a large battery for a few weeks (e.g. for a measurement campaign), you can power it with a solar panel + battery solution, or via mains power. Commercial powerbanks often turn off after having charged a device connected to them, and don't turn on again. Look for a powerbank with an "always on" feature.
As with the Partector's internal battery, most Li-Ion batteries are only specified for temperatures above 0°C. Using mains power solves such issues, but obviously leads to other limitations.

Example setup

The picture below shows an example setup that we have used successfully for ambient monitoring in Switzerland.

Intercomparing measurement results

When comparing data of different instruments that measure ultrafine particles, one nearly always finds discrepancies between different types of instruments. Reasons for this are:

Reference instruments

 The size range of different instruments is often different. The most common example for this is: Different condensation particle counters (CPC) have different lower diameter cutoffs (d50, e.g. @ 7nm; 10nm).

 Scanning mobility particle sizers (SMPS) can also be set to different size ranges.

 Condensation particle counters often have limited concentration range (e.g. up to 100'000 pt/cc) and cannot see higher concentrations, whereas the Partector 2 does. If you are measuring close to a particle source (road, airport), you might see such high concentrations.

 Just like the Partector 2, reference instruments also need regular service/maintenance. Make sure service intervals are complied with, and regularly check for warnings or errors of reference instruments.

Inlet losses

 When comparing instruments that use different inlets, losses in the respective inlet systems must be accounted for. Especially for the smallest particles, losses by diffusion can be relevant. An example: if you sample air for the Partector 2 with a 0.5m long tube, about 10% of the 10nm particles will be lost by diffusion.

Current standards

 For particle number measurement: CEN/TS 16976:2016 specifies a 7nm d50 cutoff.

 For particle size distribution measurement: CEN/TS 17434:2020 specifies a 10-800nm measurement.

 Both standards specify how particles must be sampled.

 Be aware: The CEN-compliant TSI SMPS will apply a correction for the inlet losses. If you connect a Partector 2 at the same inlet system, it does not know about these losses and will show lower concentrations than the reference.

A recent paper by Asbach et. al. compares a Partector 2 Pro with a CEN-compliant SMPS system. They corrected the Partector 2 data for the correction factor applied by the SMPS system.

Multiple Partector 2 versions

 The Partector 2 is available in a standard version where an assumption on the particle size distribution is made (lognormal, geometric standard deviation 1.9) to calculate particle diameter and particle number. The standard version reports LDSA, average particle diameter, and particle number concentration.

 Since 2022, it is also available as Partector 2 Pro, which makes no assumption on the particle size distribution, and which reports a particle size distribution (8 channels from 10-300nm). The pro version can also run in standard mode, but not vice versa. The two versions will produce slightly different results.

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Further information

For further information please also read our FAQ with some more questions and answers or browse through our list of publications with articles from other scientists.

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