15. Hydrocarbon, carbon dioxide and carbon monoxide concentration in gasoline or gas-powered vehicle emissions is measured using a 4-gas or 5-gas analyzer in accordance with the Preconditioned Two Speed Idle Test Procedure [USEPA Publication EPA-AA-TSS-I/M-90-3 January 1991 – Recommended I/M Short Test Procedures for the 1990's: Six Alternatives], published by the United States Environmental Protection Agency.