Despite global treaties and national regulations limiting toxic chemicals known as persistent organic pollutants (POPs), many of these chemicals still remain in the environment for long periods of time and accumulate in our land, water and air. These chemicals —which reach remote regions of the globe, such as the Arctic, through air currents — have dangerous effects on humans and animals. Warming of the atmosphere and changing patterns of wind and rain, due to climate change, can affect where and when these pollutants travel. However, the impact of climate on POPs — how these patterns will change, and in what direction — is not well known.
In a new study published in Environmental Science and Technology, MIT researchers assess the impacts of both climate change and future emissions on a group of POPs called polycyclic aromatic hydrocarbons (PAHs) — toxic byproducts of burning wood, coal and oil. They are the first to address the influence of climate change on the transport of PAHs.
They find that decreases in human emissions are expected to cause PAH concentrations to decline by up to 37 percent by 2050. But, climate change can either reduce or enhance that decline depending on the physical and chemical properties of different PAHs.
“We are interested in PAHs because they continue to be released into the atmosphere and their concentrations have been increasing in Arctic marine life, in contrast to most other POPs,” says Carey Friedman, a postdoc associate with the MIT Joint Program on the Science and Policy of Global Change and the lead author of the study. “We find that projected decreases in human emissions will have a stronger impact on atmospheric PAH levels in the future than changes in climate.”
However, the authors find that this statement has important caveats. As temperatures rise, due to climate change, more volatile PAHs that are currently deposited in soil and vegetation are expected be emitted — actually re-emitted — into the atmosphere.
“This represents a ‘climate penalty’ for atmospheric concentrations of more volatile PAHs, meaning that emissions reductions will not be as effective as they would have been if the climate wasn’t changing,” explains Noelle Selin, co-author of the study and an assistant professor of engineering systems and atmospheric chemistry.
In contrast, atmospheric levels of non-volatile PAHs are expected to decrease under 2050 climate conditions because their ability to be deposited into the soil and land will be enhanced.
“Our results suggest that ratios of the different types of PAHs (volatile to non-volatile) in the Arctic can be used to diagnose whether the atmosphere is experiencing greater influence from climate change or reductions in human emissions,” Friedman says.
This raises the possibility that such a technique could be used to measure the effectiveness of emissions reduction activities in the context of ongoing climate change. The study is part a series of National Science Foundation-funded research tracking how chemicals travel to remote Arctic environments and how they can be better managed. Researchers have presented the results of these studies to help inform policymakers on the most effective methods of addressing POPs such as PAHs, which are affecting humans and the environment.