SO2 Monitoring Station

Living with active volcanoes about becomes a bit easier if they are properly monitored. The entire island of Hawai‘i is liberally equipped with sensors of various types… Seismographs, tiltmeters, GPS stations, cameras, and gas monitors.

Weather and SO2 monitoring station
A remote weather and SO2 monitoring station

I came across one of these last instruments on a recent visit to Hawai‘i Volcanoes National Park, the new Kahuku Unit at the south end of the island. While walking in the gorgeous natural scenery of the park, this engineer was instantly attracted to a spindly frame of tubes standing in an old corral.

The Kahuku Cross Fence station is part of the NPS maintained Hawaii SO2 Network with stations throughout the park. The data is provided to rangers and posted on the park website to advise visitors of volcanic gas hazards while visiting the volcanoes.

Despite being surprised at finding this station I knew these stations existed and what I was looking at. With curiosity piqued I noted the cabinet was not locked… Yes, I opened it to take a peek inside.

As I build similar equipment professionally what I found inside was mostly what I expected. My peek revealed some components I was quite familiar with and a few other bits that needed a second look.

Weather and SO2 monitoring station interior
The interior of a NPS weather and volcanic gas monitoring station

The cabinet, solar panels, and charge controller are quite standard, no surprises there. The batteries for the station are in a large black plastic tub under one of the solar panels. The charge controller is a Morningstar Sunsaver 20L for lead-acid batteries.

Oddly there are three solar panels of very different sizes and vintages all mounted about the pole as if the station had been upgraded or expanded greatly and panels had been added to support increasing power needs.

Connecting the various sensors to the network is a Campbell Scientific model CR310 data logger. While network communications are provided by a cellular modem seen in the upper right of the photo using an antenna at the top of the mast.

Two SO2 gas sensors are at the bottom of the cabinet with the sensors protruding underneath and electronics units just above. These are RKI Instruments M2A series units, which according to the data sheet are rated for 0 to 6ppm at 0.01ppm resolution for SO2.

The duplicate sensors are interesting, how reliable are these gas sensors that the designer of this station felt the need to install two? The readings shown on the history for this station are quite low, no surprise as the eruptive activity at Kilauea is currently on pause.

Also mounted underneath is a Purple Air particulate meter. This meter has also been measuring good air quality lately without an actively erupting volcano about. A very different story than we experienced back in 2018 when the volcano was spewing lava and gas. This station is usually downwind of the caldera and was certainly reporting elevated volcanic emissions, locally called vog.

Above the station, at the top of the pole, are a few more standard weather sensors reporting temperature, humidity, and wind speed using a sonic anemometer. I did not note a precipitation sensor, an odd omission from a station like this.

I was not impressed by the workmanship of whomever assembled the instrument cabinet. It appeared as if the circuits were wired by a ham handed grad student with no sense of pride in their work. A snarl of cable, loose strands at the screw terminals without ferrules or spades crimped on the wires. The pile of desiccant packs at the top had clearly not been changed in quite some time and were probably saturated long ago.

Many folks who call the island home have by necessity become amateur volcanologists, keeping tabs on the latest rumblings of Kilauea and Mauna Loa. It is only a matter of time before we have another eruption and sensors like those mounted at the Kahuku Cross Fence station are once again reporting high levels of SO2 and particulates.

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

One thought on “SO2 Monitoring Station”

  1. Hey Andrew:
    Google’s news feed popped up a hackaday post about your find. I am an air quality researcher who uses similar sensors. Colleagues at MIT were setting up a network for VOG monitoring, though they used Alphasense electrochemical sensors (and I believe) in boxes assembled by undergrad students as part of a lab course:
    Usually, we need machine learning techniques to get useful data at low levels, but the sensors work quite well for high gas mixing ratios – where they would be hazardous.

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