HRVOCs 101: What, Where, and How

Sept 14, 2021

By: Erika Garcia

In the environmental industry, many of us are familiar with Volatile Organic Compounds (VOCs) but some may not know that a subset exists known as Highly Reactive VOCs (HRVOCs). These are especially important in air quality because they are involved in ground-level or “bad” ozone formation, which greatly impacts respiration for animals, plants, and of course humans. Even low amounts of ground-level ozone can make it difficult to breathe, damage and inflame airways, cause shortness of breath, aggravate lung diseases like asthma – just to name a few effects.

The state of Texas, in particular, developed regulations beginning in 2002 for controlling HRVOC emissions in the greater Houston area. These rules were created due to findings in the Texas 2000 Air Quality Study (TexAQS) that showed significantly underestimated VOC emissions compared to what was actually reported. In turn, they were also developed to meet the National Ambient Air Quality Standards for ozone and emphasize “monitoring, recordkeeping, reporting, and enforcement, rather than establishing individual unit emission rates.” The main HRVOCs that are being monitored in Houston (Harris County) are Ethylene, Propylene, 1,3-Butadiene, cis-2-Butene, trans-2-Butene, Isobutylene, and 1-Butene. Other HRVOCs include Formaldehyde, Acetaldehyde, Isoprene, and Toluene, as well as all isomers of Ethyltoluene, Pentene, Trimethylbenzene, and Xylene.

Now that you know a few of the important HRVOCs, let’s talk about sources. HRVOCs are regulated from stationary sources such as flares, fugitives, process vents, and cooling towers. Flares are primarily used as safety devices to control large volumes of pollutants via VOC destruction in refineries and petrochemical facilities. Even though ideally flares obliterate waste, they can actually promote chemical reactions into HRVOCs. Fugitives are emissions of gases or vapors from pressurized equipment due to leaks or other unintended releases. These leaks can occur at valves, flanges, seals, sample connections, and fittings. Process vents are open-ended pipes or stacks that vent either directly to the atmosphere or through a vacuum-producing system or tank (examples include distillate receiver, condenser, bottoms receiver, surge control tank, separator tank, or hot well). Cooling Towers are structures designed to regulate the temperature of various processing units. During the process of attempting to reduce heat, the water used in cooling towers can contain various leaked hydrocarbons that air flowing through the tower can strip off or can get flashed out.

As you can see, HRVOCs are largely from industrial sources; therefore, the Texas Commission on Environmental Quality (TCEQ) created a market-based cap-and-trade program that imposes annual and hourly limits on these industrial sources of HRVOCs. The HRVOC emission cap is set at 2,588.6 tons and is distributed among the different industries, as well as individual sites within their respective industries. Sites are then allowed to buy and sell allowances with other sites within their industry.

When it comes to identifying HRVOCs, they can be analyzed by EPA Methods 18 (Measurement of Gaseous Organic Compound Emissions by Gas Chromatography); TO-14A (Determination of VOCs in Ambient Air Using Specially Prepared Canisters with Subsequent Analysis by Gas Chromatography); TO-15 (Determination of VOCs in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry); as well as ASTM D1945 (Standard Test Method for Analysis of Natural Gas by Gas Chromatography) and ASTM D1946 (Standard Practice for Analysis of Reformed Gas by Gas Chromatography). Samples can then be collected in Tedlar bags, summa canisters, or cylinders.

Overall, as long as HRVOCs are carefully monitored, the goal is for ground-level ozone formation to not accelerate, which can hopefully lead to a healthier planet.

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