In addition to carbon dioxide, when humans burn fossil fuels, they release other toxic or harmful chemicals, such as methane, sulfur oxides, nitrogen oxides, lead, and mercury, into the atmosphere. The chemical methane is released into the atmosphere by agricultural activity, fracking, and other petroleum mining, as well as through the melting of the Earth’s permafrost layer — melting that is being driven by global warming.  

Air pollution can travel long distances over a short time, but it can also linger in a community for long periods. The consequences of burning of fossil fuels, both past and present, in industrial settings like power generation plants or factories are an environmental problem that can remain for centuries. As you can see from the animation above, toxic emissions from fossil fuels are an inter-state and international problem. For example, smoke from a power plant in Ohio can pollute a body of water in Massachusetts with mercury, thus highlighting the important role of pollution regulation by federal agencies like the Environmental Protection Agency (EPA) and international treaties like the United Nations' Paris Climate Agreement. 

One such incident took place in the Merrimack Valley. In March of 2011, the Hooksett, New Hampshire sewage treatment plant overflowed during a storm, dumping untreated water and millions of tiny plastic discs, used to filter sewage, into the Merrimack River.  Five days later, the discs arrived on the beaches of Newburyport, MA. Ten years later, the discs are now showing up on the beaches of European countries. A community-science effort is recording data about where the discs travel via ocean current.