“…1 ' 2 Although it is difficult to assign exact values to the many factors involved, overall estimates of the contaminant emissions for Los Angeles County have been computed on the basis of available data as shown in Table I. 3 Motor vehicle exhaust gases account for approximately 65 per cent of the hydrocarbons and 60 per cent of the oxides of nitrogen emitted. It is obvious from these figures that automobile exhaust is one of the most important contributors to smog in this area.…”