A South Coast (Los Angeles, CA) Air Quality Management District (AQMD) study reveals that emissions from the 312,000 cows in its district are an insignificant part of L.A.'s pollution. The AQMD study says heavy trucks spew 239 tons of nitrogen oxides and particulates a day, followed by ships with 35 tons and trains at 34 tons per day. The cows? About 8.5 tons of ammonia per day. The study followed a 1994 dispute when L.A.'s mayor derailed a clean air plan, urging instead a look at pollution from dairies and dirt roads. - Urban Transportation Monitor, March 1996.