socks and knocks
 n.pl.— «The seven criteria pollutants are carbon monoxide (CO); lead; sulphur dioxide (SOx) and nitrogen oxide (NOx) (often called “socks and knocks”).» —“Air Quality Regulation in Minnesota” by Mike Bull in Research Department of the Minnesota House of Representatives House Research Short Subjects (St. Paul, Minn.) Oct., 2002. (source: Double-Tongued Dictionary)

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