Questions or Comments:
You are here:

Automated Gas Chromatographs (AutoGCs) Support Information

More information about AutoGCs including what AutoGCs monitor, why, the limitations, and contact information.

Information about why the TCEQ monitors for these compounds

Ozone precursors

VOCs along with oxides of nitrogen, and solar (UV) radiation are key components in ozone formation. Individual VOCs can vary greatly in concentration and their reactivity (i.e., potential to form ozone). A key component in studying the dynamics of ozone formation in a given geographic area is the determination of the spatial and temporal variability, composition, and concentration of these individual VOCs. These data can then be used to help target control strategies to minimize ozone formation, especially if VOCs are determined to be the limiting factor in ozone formation reactions. TCEQ operates Photochemical Assessment Monitoring Stations (PAMS) as a partner in this national monitoring effort.

AutoGC analysis can measure ambient levels of a number of VOCs which are of interest from an ozone formation standpoint even when their concentrations are too low to cause direct health effects. These VOCs include the highly reactive VOCs (HRVOCs) that the TCEQ has identified as major contributors to ozone formation in the Houston area. These HRVOCs are: ethylene, propylene, 1,3-butadiene, and butenes (c-2-butene, t-2-butene, and 1-butene). These data are made available to TCEQ modelers, policy makers, EPA, local industries and the public.

Air Toxics

There are currently 188 hazardous air pollutants (HAPS), or air toxics, regulated under the Clean Air Act (CAA) that have been associated with a wide variety of adverse health effects. A subset of the 188 toxics thought to have the greatest impact on the public and the environment in urban areas has been identified as the Urban Air Toxics Strategy compounds of interest. This subset of 33 compounds includes volatile organics, semivolatile organics, and metals. Two of the six compounds identified as the risk drivers in the strategy, benzene and 1,3-butadiene, are volatile organics which are amenable to AutoGC analysis. Data for these two target compounds as well as all other target compounds from this analysis are forwarded to TCEQ Toxicology Section to identify any potential health impacts that might be associated with exposure to the measured concentrations.


AutoGCs are designed to collect data at a given sampling location over time. These instruments can be configured to automatically provide speciation data for 1 to over 55 targeted VOCs. However, the more extensive the list of compounds the more difficult it becomes to ensure that any single compound is correctly identified and quantitated at the time of initial data capture. Changes to compound identification and concentration are not uncommon during this validation process. Therefore, it is vital that the data user is aware of the high degree of uncertainty in the unvalidated data and any actions or decisions based on unvalidated data should be made with this in mind.

Contact information