This manual provides the department’s instruction to inspection stations and inspectors for conducting the vehicle emissions inspection in counties with vehicle emissions inspection and maintenance (I/M) programs. This manual supplements the “Rules and Regulations Manual for Operation of Official Vehicle Inspection Stations,” which provides instructions for the annual safety inspection in those counties.
The design of the IM program is to concentrate on specific pollutants found in vehicle exhaust emissions. Those pollutants are carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). It is one of many similar programs in counties across the U.S. having air quality below the National Ambient Air Quality Standard.
Carbon monoxide is a colorless, odorless, and tasteless gas sometimes found in urban areas in concentrations that can be harmful to people. It is a by-product of combustion and the automobile is the single largest source of this pollutant.
Hydrocarbons are organic compounds composed of hydrogen and carbon. The energy in such compounds is released when combined with oxygen during combustion. Most engine fuels, such as gasoline, propane, methane, etc., contain hydrocarbons and some portion remains after combustion. Hydrocarbons and nitrogen oxides react with sunlight and warm temperatures to form ground-level ozone. Ground-level ozone, a main ingredient in smog, can cause upper respiratory problems and lung damage.
Nitrogen oxides, or NOx, is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2), along with particles in the air, is often seen as a reddish-brown haze (smog) over many urban areas. During combustion, high heat and pressure will cause nitrogen to combine with unused oxygen.
The specific vehicle emissions test used in the I/M program area or county focuses on the pollutant problem of the area.
The I/M program is applicable in all affected counties. The term "affected counties" applies to all counties classified as nonattainment, where the State Implementation Plan (SIP) requires an I/M program and “participating” counties that voluntarily enter the program in an effort to avoid classification as non-attainment.
In this manual, the affected counties are located in the following areas: Dallas/Ft Worth area (Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, and Tarrant counties), Houston/Galveston area (Brazoria, Ft Bend, Galveston, Harris, & Montgomery counties), El Paso area (El Paso County), and the Austin area (Travis and Williamson counties).
In El Paso, Travis and Williamson counties, the I/M program focuses on the reduction of carbon monoxide and hydrocarbon emissions. In all other affected counties, the focus is the reduction of carbon monoxide, hydrocarbon, and oxides of nitrogen emissions from designated vehicles.
This manual consists of five (5) chapters. Chapter 1 is an introductory chapter, which explains the purpose and goals of the program. Chapter 2 describes the Acceleration Simulation Mode 2 (ASM2) emissions test performed on 1995 and older designated gasoline powered vehicles in all affected counties except El Paso, Travis and Williamson counties. Chapter 3 describes the On-Board Diagnostic Second Generation (OBDII) emissions test performed on 1996 and newer designated gasoline powered vehicles in all affected counties. Chapter 4 describes the Two Speed Idle Test (TSI), which is the type of emissions test performed on all 1995 model year and older designated vehicles in El Paso, Travis and Williamson counties. Chapter 5 is a reference section. Additionally, Chapter 5 contains Rule 23.93 (37 TAC §23.93), which incorporates this manual into the Texas Administrative Code.