Volatile Organic Compounds

Volatile Organic Compounds (VOCs) are a large group of chemicals that are prevalent in the air that we breathe because they are used in industry, agriculture, transportation, and day-to-day activities around the home and workplace. Common examples of VOCs that may be present in our daily lives are benzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, toluene, xylene, and 1,3-butadiene.

Thousands of VOCs have been manufactured for use—many of these chemicals are toxic and can pose human-health or ecological concerns in the environment. VOCs may or may not be able to be smelled, and smelling is not a good indicator of health risk. You can check the Consumer Product Information Database (CPID) to learn more about what’s in common household items.

VOC Sampling

Ambient air sampling for VOCs involves collecting a representative sample for analysis. There are several different methods that this may be accomplished. The methods that LDEQ uses include:

• Direct ambient air analysis (methane/non-methane organic carbon analyzer)
• Whole air sampling with specially prepared canisters
• Direct in-field sampling and concentration using a sorbent tube and cold trap

Our methane/non-methane organic carbon analyzer (NMOC) continuously samples the air directly and provides the results. Methane is an important greenhouse gas and the NMOC represents all of the remaining VOCs in the sample. When the concentration of the NMOC remains at a predetermined concentration, usually 1 ppmC, a canister sample may be triggered and a twenty-five-minute sample will be collected. This is done in an attempt to collect the highest concentrations in order to facilitate the identification of the compounds causing the higher results.

Specially treated and prepared canisters are used for collecting whole air samples for later analysis.

Though sample duration may span several lengths there are four that we primarily use.

 

 

 

 

 

• Grab Samples – These samples are taken by simply opening the valve to the evacuated canister allowing it to draw in the sample until it reaches atmospheric pressure. These samples are frequently taken during times of expected higher contaminations and provide only a “snapshot” of the current conditions at that instance.
• Strike Samples – These have a duration of 25 minutes (0.42 hours). As explained above, they are initiated when the NMOC concentration on a methane/NMOC analyzer remains at a preset level (usually 1.0 ppmC) for 10 minutes.
• 3-Hour Samples – These are taken as part of the Photochemical Assessment Monitoring Station (PAMS) protocol. They are used to determine how various VOCs change throughout the day.
• 24-Hour Samples – May be compared to a 24-hour standard and may be used to calculate an annual average. An annual average is calculated by averaging the results of 24-hour samples taken once every six days for one year.

VOC Analysis

There are two different analyses conducted on samples taken in canisters. Either or both may be performed.

• TO12MOD – Method for the Determination of Non-methane Organic Compounds (NMOC) in Ambient Air Using Cryogenic Preconcentration and Direct Flame Ionization Detection (PDFID). This is the method used for the analysis of ozone precursor organic compounds or PAMS compounds. This analysis usually provides results for 30 different hydrocarbons.
• TO15MOD - Determination of Volatile Organic Compounds (VOCs) In Air Collected In Specially-Prepared Canisters And Analyzed By Gas Chromatography-Mass Spectrometry (GC/MS). This is the analysis of choice for our air toxics program and usually includes the results of 59 compounds. Many of these compounds are included in the hazardous air pollutants (HAPs) listed in Title III of the Clean Air Act. Use of the mass spectrometry also allows for the tentative identification of compounds not included in the calibration standard.

VOC Data

Canister data collected by LDEQ may be searched from this site:

https://internet.deq.louisiana.gov/portal/DIVISIONS/AIR-MONITORING/CANISTER-DATA

Please see the LDEQ Disclaimer State for Air Quality Canister Data for the LDEQ’s complete disclaimer statement.