Photo ©Thinkstock.com/George Doyle.
The Houston-Galveston-Brazoria (HGB) region—which includes Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery, and Waller counties—is home to the fourth largest city in the USA, and is among the nation’s fastest-growing metropolitan areas in terms of people, traffic, and industry. When you consider the massive size of the region’s industrial complex along with its rapid economic and urban population growth, it is easy to see how addressing air quality in the region can be a highly complex undertaking.
HGB, however, continues to make significant progress in addressing air quality challenges, and for the first time the area is meeting current ozone standards. The TCEQ has been at the forefront of efforts to improve air quality, aggressively targeting specific pollutants and successfully employing a variety of strategies and initiatives.
1997 8-Hour Ozone Design Values Trending Downward
Attainment of the 8-hour ozone National Ambient Air Quality Standard (NAAQS) in the HGB region poses unique challenges due to economic and population growth, complex ozone formation chemistry, unique weather patterns, and the magnitude of the emissions reductions that are needed for attainment. Ozone levels for the region, however, have been trending downward since 2000. The 8-hour ozone design values decreased by 25 percent from 2000 to 2009, and 2009 data indicates that the HGB area has reached a design value of 84 parts per billion (ppb), which is below the 1997 ozone standard.
TCEQ Strategies Reduce NOx Emissions
Mobile sources (on-road and nonroad) account for 62 percent of the NOx emissions for the area. Point and area sources contribute the remaining 38 percent. While the state has jurisdiction over point and area source emissions, it must rely on the federal government to help reduce emissions from mobile sources.
Strategies employed by the TCEQ to reduce NOx emissions from stationary sources have required industry to reduce NOx emissions by approximately 80 percent. These initiatives—which include an emissions cap-and-trade program; limits on other minor source sites with combustion equipment such as boilers and process heaters; and restrictions on operating stationary diesel engines for testing and maintenance purposes between 6 a.m. and noon—were responsible for a reduction of more than 180,000 tons per year of NOx from 1997 through 2008.
Benzene Reduction in the Lynchburg Ferry Area
“Benzene concentrations in the Greater Houston area have decreased considerably in the last four years and, in most cases, are no longer at a level of potential concern,” says TCEQ Chief Engineer Susana Hildebrand.
One success of note is in the Lynchburg Ferry area, where annual benzene concentrations have been elevated above the long-term air monitoring comparison value since 2003. TCEQ and industry initiatives to reduce emissions in the area have resulted in an overall decrease in annual average benzene concentrations of 65 percent from 2005 to 2008, as indicated by monitored concentrations.
The industry initiatives include signing emission-reduction agreements with the TCEQ, forming the Monument Area Air Quality Focus Group, and using an Environmental Monitoring Response System to automatically alert area industries when the monitor registers an elevated concentration, so that investigations and process changes can be quickly made.
The TCEQ has conducted frequent and thorough investigations of facilities in the area, which have led to corrective actions directed at reducing benzene emissions. In addition, the agency has coordinated investigations with the industry monitoring group and the United States Coast Guard to identify and reduce benzene emissions from barges in the Houston Ship Channel.
The average benzene concentration for 2009 was 0.892 parts per billion by volume (ppbv), compared to 1.10 ppbv in 2008—which represents an additional reduction of about 19 percent. As a result, benzene was removed from the Air Pollutant Watch List for the Lynchburg Ferry area in January 2010.
Industry Agreements Lower 1,3-Butadiene in Milby Park
Butadiene is emitted from a variety of sources, including gasoline- and diesel-powered vehicles, industrial plants, and the combustion of other fossil fuels or biomass.
Based on monitoring data, in 2004 the TCEQ identified a need to reduce 1,3-butadiene levels in Houston’s Milby Park area. The agency implemented a number of surveillance strategies, identified specific emissions sources at Texas Petrochemicals and Goodyear Tire and Rubber, and contacted these companies to discuss air quality concerns.
The TCEQ then entered into Voluntary Emission Reduction Agreements with the two companies, laying out emission-reduction goals, actions to meet those goals, and timelines for those actions. The companies were required to install fence-line monitors and use the GasFindIR camera to identify leaks. A notification system was established that enabled the companies to immediately investigate their plant activities in response to elevated emission levels monitored at Milby Park.
As a result of the agreements, 1,3-butadiene levels at the Milby Park monitor were 78 percent lower in 2008 than in 2004 and are no longer considered of potential health concern. In 2009, 1,3-butadiene was removed from the Milby Park Air Pollutant Watch List.
Cooperative Efforts Lead to Reduction of PM2.5 at Clinton Drive
Until 2006, all the PM2.5 monitors in the Houston area had recorded design value readings lower than the NAAQS of 15.0 micrograms per cubic meter (µg/m3)—except for the monitor on Clinton Drive, a heavily traveled road across the street from the entrance to the Port of Houston Authority (PHA).
To determine the cause of the elevated readings at this monitor, the TCEQ funded a series of in-depth studies. The studies concluded that the high readings were confined to a small area near the monitor, which is in close proximity to heavy truck traffic at the port entrance, unpaved shipyards along the Houston Ship Channel, and railroad tracks that run parallel to the road.
To remedy the situation, the TCEQ worked in cooperation with the PHA, the City of Houston, Harris County, and local industry. Subsequent readings, in 2009, at the Clinton Drive monitor showed an annual average of 12.6 µg/m3 of PM2.5 that translates to a design value of 14.1 µg/m3 for 2007 through 2009.
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