Auto Smog Inspection at Idle Only, Part II: Oxides of Nitrogen 710071
Maintenance programs indicate that exhaust emission controlled cars with hydrocarbon (HC) emissions above 400 ppm or carbon monoxide (CO) above 2.25% will have emissions reduced by proper maintenance. Distribution curves of recent surveillance data show that one-third of the 1966-1969 cars have emissions above these assured reduction levels.
Calculations show that maintenance based on reducing high emitters of HC and CO should reduce total HC by 19%, CO by 30%, but increase oxides of nitrogen (NOx) by 9%. Further calculations show that maintenance based on reducing high emitters of HC, CO, and NOx should reduce total HC by 20%, CO by 25%, and NOx by 6%.
The inclusion of NOx testing along with HC and CO in the idle inspection test method is nearly as effective in identifying high emitters of HC, CO, and NOx as the longer seven-mode test method.