A Potent Greenhouse Gas Used to Make Solar Panels Is on the Rise
Nitrogen trifluoride emissions in the United States, while very low compared to carbon dioxide, could be an easy target in the fight against climate change.
US emissions of a greenhouse gas thousands of times more potent than carbon dioxide have expanded tenfold over the past two-and-a-half decades, according to fresh government data.
And one reason - wait for it - is America's increasing reliance on solar power.
The gas, nitrogen trifluoride, or NF3, is a key chemical agent used to manufacture certain types of photovoltaic cells for solar panels, as well as semiconductors and LCD flat screens.
NF3 is produced in minuscule quantities compared to carbon dioxide and now adds only a wafer-thin margin to America's total greenhouse gas emissions, while carbon dioxide makes up 82 percent and methane nearly another 10 percent. But researchers warn NF3 is dangerous due to its devilish efficiency in trapping energy, and long atmospheric lifespan of up to 740 years.
NF3 is thought to be 17,200 times more potent than carbon dioxide as a greenhouse gas, according to the U.N. Intergovernmental Panel on Climate Change.
"By itself, NF3 is not going to create a climate problem," said Dr. Michael Prather, a professor of earth system science at the University of California, Irvine, who has tracked nitrogen trifluoride emissions. "But everything adds up. Everybody should be paying attention to the pieces that all add up."
The 1,057 percent increase in US annual emissions of NF3 from 1990 to 2015 compares to an increase of 5.6 percent in carbon dioxide emissions, according to EPA data in a recently-published draft of a new report, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2015. The report said overall emissions fell 2.2 percent in 2015 as the country continued to swap coal for natural gas and a warmer winter reduced demand for heating fuel.
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To be sure, it's easier to achieve impressive-looking growth rates from a low starting point.
As of 2011, total NF3 emissions equalled only 0.06 percent of the amount of greenhouse gas emissions contributed by CO2 using an apples-to-apples comparison, according to a study led by researcher and University of Edinburgh climate specialist Dr. Tim Arnold, then with the Scripps Institution of Oceanography.
But both production and industrial use of NF3 has soared since 1990, and analysts project continued expansion over the coming decade amid strong demand for solar electricity, computers, smartphones and televisions. The NF3 market is expected to rise 13 percent every year and reach $1.2 billion by 2020, according to Hexa Research, a California-based research and consulting firm.
Meanwhile, the US market for solar power nearly doubled in 2016, according to a report by GTM Research and the Solar Energy Industries Association.
Environmentalists are quick to say solar panels still make sense, despite the associated NF3 discharge.
"The impact of NF3 as a global warming gas is big on a per-molecule basis, but the benefits of carbon-free energy from solar panels swamp the negative impacts due to NF3 emissions," said Tim Donaghy, a senior research specialist for Greenpeace.
"Lifecycle analyses of solar photovoltaic manufacturing show that the emissions of NF3 are offset within the first one-to-four months of the solar panel's life," Donaghy said, citing a 2010 study.
NF3 is essentially a cleaning agent that can be broken down into fluorine plasma to clear away excess silicon from production chambers. It is stable and transportable, cleans faster than other available options, and most of it is eliminated during use.
But a small percentage leaks into the atmosphere. The question researchers have asked in recent years is exactly how much gets leaked.
"People are doing a better job of leaking less, but it's still a fair amount, considering production is going way up," said Dr. Prather. "The fraction that gets leaked seems to be declining a bit, but it's not declining fast enough."
NF3 gained popularity as a substitute for even more harmful global warming gases that were used in the same types of manufacturing. That's why the country's top producer of NF3, a company known as Air Products and Chemicals Inc., received an award from the EPA in 2002 for its role in helping to safeguard the climate. A company spokesperson for Air Products didn't respond to requests for comment.
The good news is that despite increased chemical production and use, EPA figures suggest NF3 emissions in the United States - which are calculated based on data reported by the semiconductor industry - may have plateaued in recent years.
The bad news is, those numbers might be low.
In 2008, a team of researchers released a study comparing atmospheric levels of NF3 against the amount that industrial players reported they had emitted.
The air samples revealed the presence four-and-a-half times more NF3 in the atmosphere than expected given the amount of emissions reported by industry, according to the lead author of the study, Dr. Ray Weiss, a geochemistry professor at the Scripps Institution of Oceanography.
"In the end, the climate only cares about what you actually emit, not what you report," Dr. Weiss said.
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Asked whether the most recent US NF3 emissions numbers from the EPA should be considered accurate, Dr. Weiss said, "It's a really hard question to answer. There's a lot of guesswork going into it. But it is plausible to think emissions have flat-lined, partly because most of the manufacturing is not in our country."
He added, "The big question is: What's going on in Asia?"
Almost half of NF3 demand now comes from Asian manufacturers, according to Hexa Research.
Yet Dr. Weiss said he sees reason for optimism.
"The industry has done a good job of responding to environmental concerns," he said. "The amount of NF3 that is used has risen exponentially. But they've also managed to use it more efficiently and to cut leaks."
The opportunity represented by NF3, according to Dr. Weiss, is that it represents "low-hanging fruit" for environmentalists looking for ways to reduce global greenhouse gas emissions, and flummoxed by the difficulty of limiting carbon dioxide.
"These really potent gases are a really good place to start, because you get a lot of good bang for your buck," he said.
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