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Topic: Airshed & Watershed

40 years ago today, the United States Congress voted to adopt the Air Quality Act. This was our nation's first federal act aimed at reducing pollution: it authorized the Department of Health, Education, and Welfare to establish federal air quality standards and pollution standards. It also directed states and local entities to monitor their airsheds, the air supply of a given region.

We're marking the occasion with a look at airshed, a word that entered public consciousness during that era. As mentioned, airshed names the "air supply of a given region;" it is used especially to refer to the "geographical area covered by such an air supply." Airshed was formed on the model of watershed, the term for "a region or area bounded peripherally by a divide and draining ultimately to a particular watercourse or body of water."

Watershed is believed to have originated in the German wasserscheide; it's easy to understand the water part, but let's shed a little light on the shed. This shed is unrelated to outbuilding sort of shed; the shed under the microscope has a linguistic ancestor meaning "to divide; separate" and once meant "distinction; difference;" those senses have been discarded—okay, shed—and shed nowadays names a "divide of land."

Questions or comments? Write us at wftw@aol.com Production and research support for Word for the Wise comes from Merriam-Webster, publisher of language reference books and Web sites including Merriam-Webster's Collegiate Dictionary, Eleventh Edition.

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