The finding was unexpected. The researchers, from Oregon State University, weren't even looking at the power plant, or into mercury emissions at all. They were studying a different pollutant, polycyclic aromatic hydrocarbons (PAHs), which can be highly toxic. The researchers were tracking how PAHs generated by air pollution in Asia moved across the Pacific, and noticed a huge drop between their 2010 and 2011 data. The PAH levels dropped by 72 percent, and another type of pollutant, oxy-polycyclic aromatic hydrocarbons (OPAHs) dropped by 40 percent.