Air Pollution Data Collected by Automated Gas Chromatographs (AutoGCs)
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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.
Limitations
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
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