POWER plant operators in the US are keen to trade emissions credits with each
another as a way of staying within overall pollution limits. But unless the
trades are carefully monitored, the strategy could make things worse.
Researchers in Texas, where emissions trading is already under way, have
found that the location where pollutants are emitted can be just as important as
the quantity. Get it wrong, and some kinds of pollution worsen.
Nitrogen oxides (NOx), for example, react with volatile organic compounds to
produce smog-forming ozone. If power plants near urban areas buy credits to
belch out NOx, then smog can rise to levels that aggravate breathing problems.
“There are scenarios where you can reduce NOx by half and wind up with a worse
case of pollution than what you started with,” says David Allen from the
University of Texas in Austin.
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The Texan Emissions Banking and Trading Program has tried to tackle this
problem by splitting the state into large areas, and only allowing companies to
trade with others in the same area. But in the first detailed study of NOx
trading, Allen and his team have found this isn’t good enough.
The researchers created a computer simulation in which 50 power plants in
eastern Texas were allowed to trade with each other. They found that 1 in 10
trading scenarios created a quarter more ozone pollution than if the same cuts
were spread equally across all the power plants. And a few trades in the wrong
direction resulted in worse pollution than if there had been no emissions
reductions at all. On the other hand, some trades virtually doubled the
reduction of ozone, they will report in an upcoming issue of Environmental
Science and Technology.
Allen says that stopping the top 10 per cent of polluters from buying NOx
credits would solve a lot of the problems. Matthew Baker from the Emissions
Banking and Trading Program says they are taking the scientists’ views on board,
and accepts they may need to fine-tune their trading system.
Allen suspects the same thing might happen with other pollutants that cause
local problems and have complex interactions with the environment—like
mercury, for example.