> For the complete documentation index, see [llms.txt](https://docs.aethlabs.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aethlabs.com/microaethalometer-tm-ma450/quick-start-guide/built-in-nafion-dryer.md).

# Built-in Nafion Dryer

The MA450 is available with an optional built-in Nafion dryer for conditioning the aerosol sample in high-humidity outdoor deployments. Changes in relative humidity can alter the size and optical properties of particles, so drying the sample before measurement improves data quality in humid environments.

The dryer is a factory-installed option. When ordered, it ships pre-installed inside the MA450 enclosure, so there is no customer installation procedure. The needle valve control for the Nafion dryer is pre-set at the factory, but the dryer pump flow should be adjusted for different instrument sampling flow rates.

It is an active dryer that removes water vapor from the sample using dry purge air driven by an internal purge pump inside the enclosure. No external pump or pump-port connection is required.

## Powering the Dryer Pump

The dryer's purge pump is internal to the MA450 enclosure. When the built-in dryer is installed, a second 12V power supply must be connected in addition to the instrument power to run the dryer and its internal pump. Connect the second M8 sealed circular connector cable of the 12V outdoor rated power adapter to the MA450 circular M8 connector labeled DRYER 12V DC IN. See [Powering the MA450](/microaethalometer-tm-ma450/quick-start-guide/03-powering-the-ma450.md).

## Dryer Configuration

<figure><img src="https://272274374-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F1fOQ2MnLWcq0ntHW3LLY%2Fuploads%2Fgit-blob-01332ff4d09c3307b87550bf8899298aecc966a2%2Fma450-nafion-dryer-needle-valve.jpg?alt=media" alt="Open MA450 outdoor enclosure showing the built-in Nafion dryer assembly, with the needle valve circled and labeled in red"><figcaption><p>The built-in Nafion dryer assembly inside the open MA450 enclosure. The needle valve is circled and labeled.</p></figcaption></figure>

### Set the needle valve

Turn the needle all the way in (until you start feeling elevated resistance), then loosen the valve by 5 half-turns (900 degrees).

### Set the pump drive

Avoid the vacuum pump pulling less than the aethalometer pump is providing. Set the pump by reading from a flow meter and adjusting the flow until it is at 150% of the maximum flow rate of the instrument (300 ml/min).

The flow depends on the needle valve. If the flow is already under 300 ml/min, open the needle valve a little. Then lower the pump drive via the potentiometer until the flow starts to decrease by more than \~20 ml/min.