XPRIZE Competition Poses Ocean Acidity Challenge
Sep20

XPRIZE Competition Poses Ocean Acidity Challenge

Today’s post is by Puneet Kollipara, intern at C&EN and an aquatic acidity aficionado. Humans pump carbon dioxide into the atmosphere by burning fossil fuels, but not all of it stays in the air. About one-fourth of the released carbon dioxide dissolves into the oceans, where it has been lowering the global average pH of seawater and thereby threatening aquatic ecosystems. Unfortunately, the ocean is as complex as it is spacious, and ocean pH doesn’t change uniformly across its depth. To get the full picture, scientists need a lot of data, but current techniques for monitoring ocean pH are generally expensive, aren’t always reliable, and can’t go very deep underwater. Right now, the U.S. National Oceanic and Atmospheric Administration (NOAA), for instance, has 18 ocean-chemistry monitors at various locations—more than anyone else in the world—but none of these sensors takes measurements below surface waters. “As you can imagine, that does not really represent the global oceans very well,” says Christopher L. Sabine, an oceanographer at NOAA’s Pacific Marine Environmental Laboratory. A 22-month competition launched by the XPRIZE Foundation, a nonprofit aiming to spur technological innovation for society’s betterment, seeks to change that. The newly announced $2 million Wendy Schmidt Ocean Health XPRIZE calls on innovators of all stripes, both professional and amateur, to design better pH-measurement technologies. “The idea with the XPRIZE is to develop robust, inexpensive sensors that can be deployed much more easily,” says Sabine, whose NOAA lab is partnering with XPRIZE for the competition. Half of the $2 million prize will be awarded for the development of an affordable, reliable sensor, Sabine says. The other half will go toward a system that can accurately profile pH changes, including at great depths; such an instrument might start deep in the ocean and take real-time measurements as it’s lifted to the surface. Two types of instruments are currently in mainstream use for measuring ocean pH, but both have significant drawbacks. The first type, potentiometric sensors, involves probing a water sample with a device containing two electrodes. One electrode is enveloped in a semipermeable membrane that lets ions pass through, and the other is exposed directly to the water as a reference. Acid hydrogen ions flow from the seawater across the membrane, and a voltmeter measures the resulting electric-potential difference compared with the reference electrode. The sensor can use that measurement to calculate the water’s pH: The more H+ ions there are, the more that flow across the membrane, and the greater the resulting voltage. One drawback of pH electrodes, however, is that they’re very sensitive to the presence of other ions in seawater, which can also flow across...

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