Investigators from the government and social media have spent months trying to find out where a mystery smell that swept through Southwest Washington on its way to Portland in September originated. Washington’s Department of Ecology confirmed Wednesday it had a likely answer for part of the stink: the Smurfit Westrock paper mill in Longview, Washington. Longview is home to several paper mills and wood pulp facilities that use sulfur-based compounds to break down wood products. In October, Westrock said it didn’t believe it contributed to the smell that had concerned residents in the roughly 60-mile stretch between Longview and Portland. …While the answer does not definitively point the finger at Westrock for the odd odor, the Ecology Department said it could say for certain that the company did not emit chemicals in concentrated enough amounts to threaten human health or the environment.