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The Statesman


    BNL Scientists Help to Identify the Source of Excessive Ozone Pollution

    Using data from one of the most comprehensive U.S. air pollution studies everconducted, scientists at the U.S. Department of Energy’#146;s Brookhaven NationalLaboratory (BNL) have identified specific volatile organic compounds (VOCs)as key sources of excess ozone smog in industrial areas of Houston, Texas.

    These samples appear to be different from traditional sources of ozone pollutionin typical urban areas around the country. According to the authors, specificefforts to control these industrial emissions of VOCs might be necessary tocontrol Houston’#146;s ozone problem

    ‘A clear understanding of the complex causes of ozone pollution will helpto identify cost-effective ways to control smog and protect public health,’said atmospheric chemist Larry Kleinman, one of the lead BNL researchers onthe study.

    Traditional efforts to control ozone have focused on limiting emissions ofprecursor chemicals such nitrogen oxides (NOx) and/or VOCs, which are emittedfrom automobiles, power plants, and other industrial sources and form ozonewhen they react with sunlight in Earth’#146;s atmosphere. But despite improvementsin air quality due to more stringent emission standards, many areas still exceedozone standards.

    To get a better understanding of the ozone problem, the BNL team participatedin the Texas 2000 Air Quality Study, a collaborative air pollution project involvinghundreds of researchers from more than 40 public, private, and academic institutions.This study was led by Peter Daum, an atmospheric chemist at BNL.

    During August and September of 2000, the scientists conducted air-samplingflights over the Houston-Galveston area ‘#151;which experiences the country’#146;shighest ozone levels’#151; in a specially equipped aircraft operated by theDepartment of Energy (DOE).

    The scientists flew over ‘clean’ background areas and over urbanand industrial areas with high emission rates of nitrogen oxides and volatileorganic compounds, as well as downwind from these sources in regions where ozoneis expected to form.

    On each flight, researchers measured levels of ozone, ozone precursors, andphotochemical oxidation products. They were then able to calculate the ozoneproduction rate for each of the flight areas. For the present paper, they comparedthe Houston findings with data collected during several previous DOE-sponsoredair quality studies over Nashville, New York, Phoenix, and Philadelphia.

    Ninety two air-sampling flights were conducted in the five-city study. On 13flights, ozone concentration exceeded the 120 parts per billion federal standardset by the Environmental Protection Agency (EPA) to protect human health. Nineof those flights were in Houston.

    These results agree with data collected by the EPA at ground level. Over thepast five years, 15 of the highest 25 ozone concentrations recorded in all ofthe United States were in the Houston-Galveston area.

    ‘We found that most of Houston resembles other urban areas in its concentrationof ozone precursors and ozone production rates,’ Daum said. ‘The industrialHouston Ship Channel region, however, the location of one of the largest petrochemicalcomplexes in the world, has a distinctive chemistry.’

    There, very high concentrations of VOCs not seen in the other cities, or inthe other parts of Houston ‘#151;specifically ethene, propene, and butenes’#151;lead to excessive production of ozone.

    ‘Calculations based on the aircraft measurements show that the ozone productionrate in the Houston Ship Channel region can be as much as five times higherthan occurs in the other four cities or in non-industrial parts of Houston,’Kleinman said. ‘This extra kick in the photochemistry is a direct resultof the high concentrations of VOCs emitted by industrial facilities.’

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