New Technology Offers a Real Time Close-up Look at Emissions
by Vicki Wolf
Reducing toxic air pollution and petrochemical industry emissions that contribute to the production of ozone are critical to public health and mitigation of global warming. There have been reductions in Houston area industrial plant upset events and air toxins, but they are not adequate according Neil Carman, Lone Star Sierra Club air quality director. “Houston still fails to meet old one-hour ozone standards of 125 ppb, as well as the old eight-hour ozone standard of 85 ppb, and the new eight-hour ozone standard of 75 ppb.”
“The only ‘safe’ level of exposure to known human carcinogens like benzene is zero,” Carman continues. “Too many communities face a terrible assault of chemical pollution from petrochemical plants every day where they live.”
Knowing precisely where the emissions come from and what they contain is essential in the quest to reduce emissions, but emissions continue to be underreported. “Industry numbers for VOCs (volatile organic compounds) are bogus,” says Carman. “They guess at what is coming out.”
Most of the Texas Commission on Environmental Quality’s (TCEQ) monitoring for ozone and toxic air pollution is conducted outside refineries and plants with auto-gas chromatograph readings taken over 45 minutes, according to David Manis, TCEQ monitoring manager. “We’re always looking at new equipment for better time resolution,” he says. “It also needs to be cost effective, rugged and reliable.”
New emissions monitoring technology promises to take the guesswork out of emissions from smokestacks and flares. The Differential Optical Absorption Spectrometer (DOAS) makes it possible to directly monitor emissions from flares, smoke-stacks and other sources inside and outside plants and refineries, and in the future may be used in real time. The instrument can differentiate between types of pollutants by measuring the absorption of light - each pollutant has its own unique absorption pattern.
DOAS was used in the recent Study of Houston Atmospheric Radical Precursors (SHARP), a $3 million project supported by Texas Environmental Research Consortium TERC. Houston Advanced Research Center (HARC), the University of California in Los Angeles (UCLA) and Aerodyne Research, Inc. were involved in the study, as well as Texas universities such as the University of Houston, Texas A&M, and Rice.
UCLA set up one variety of DOAS on the Moody Tower Dormitory at the University of Houston, which shot its own light at mirrors mounted at different levels around downtown Houston. The researchers also set up other varieties of DOAS in the Ship Channel, Texas City and at Mt. Bellvieu, complemented by other techniques, to measure formaldehyde from flares and other large industrial releases in a sub-experiment known as FLAIR.
It has been suspected by scientists who study air pollution in the Houston Ship Channel that some pollutants and chemicals involved in ozone production are being left out in regulatory efforts described in the State Implementation Plan (SIP) for reducing ozone. Use of DOAS is proving they are right.
Radical precursors are important components in the chemistry of ozone because without them, volatile organic compounds (VOCs) make much less ozone. By using DOAS, researchers have discovered that the radical precursor, formaldehyde, needs to be considered a primary rather than just a secondary pollutant. And there is much more of it coming directly from refineries and other petrochemical facilities than had previously been reported or suspected. In one of the field studies in Texas City, researchers set up both Imaging and Multiple Axis versions of DOAS. Plumes of primary formaldehyde were immediately detected. “What we found was quite astounding. Emissions from all of Texas City measured one-and-a-half tons of formaldehyde per day on average: not one but two orders of magnitude more than anyone expected,” says Eduardo (Jay) Olaguer, HARC air quality research director. “When we quoted these findings to industry, they were aghast.”
Up until this discovery, the petrochemical industry and the Texas Commission on Environmental Quality (TCEQ) considered formaldehyde a secondary product of chemical reactions within the atmosphere. Now it’s clear that formaldehyde is an important pollutant in combustion plumes, such as those emitted from industry flares. The state’s current plan for reducing ozone doesn’t take into consideration the role this primary formaldehyde plays, according to Olaguer. Formaldehyde decomposes in sunlight and unleashes primary radicals that VOC’s can latch onto and make ozone. When highly reactive VOCs (HRVOC) come in contact with formaldehyde, they make ozone very quickly. The formaldehyde speeds up ozone production - it’s like “instant ozone.”
The Houston area has about 400 emergency flares - the largest and least understood sources of pollution in the region, according to an article in the Houston Chronicle. Formaldehyde from flares may increase Houston’s ozone by as much as 30 parts per billion (ppb).
The SHARP project also utilized the Aerodyne Mobile Laboratory, equipped with a suite of instruments that can measure pollution concentration for a very large number of pollutants, including VOCs, nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO) and carbon dioxide (CO2). The mobile lab observed toxins such as benzene as well as particulate matter. The instruments also kept track of wind speed and direction, temperature and humidity.
With this array of technology, the researchers could easily identify the source of pollution by its unique signature. While driving along the street in the mobile lab researchers know that the pollution that contains NOx is from the tailpipe of the truck driving by, and the plume that contains SO2 is from the refinery. “It’s detecting pollution in real time,” says Olaguer. The researchers pinpointed the pollution plumes and identified some of the pollutants with DOAS, and used the mobile lab instruments to fill in the blanks on the other pollutants that could not be detected with DOAS, all while operating outside facility fence lines without the need for permission from industry. In addition to radical precursors such as formaldehyde, nitrogen dioxide (NO2), sulfur dioxide (SO2), and nitrous acid detected by DOAS, the Aerodyne Mobile Laboratory observed benzene, olefins, and other VOC plumes. Researchers noted in preliminary findings from SHARP that “there are still very large petrochemical emissions of air toxins such as benzene.”
While some DOAS technology is available for commercial use, some of the specific varieties used in SHARP, as well as many of the complementary real-time monitoring instruments, are still only deployed in research settings. “We have demonstrated the concept of this technology in the field,” Olaguer says. “Already we have very encouraging results that indicate that this will be very useful down the road.”
