Editorial Type:
Article
Article Type:
Research Article

Observation-Based Assessment of the Impact of Nitrogen Oxides Emissions Reductions on Ozone Air Quality over the Eastern United States

Edith Gégo Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration, and U.S. Environmental Protection Agency, Research Triangle Park, North Carolina

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P. Steven Porter University of Idaho, Idaho Falls, Idaho

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Alice Gilliland Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration, and U.S. Environmental Protection Agency, Research Triangle Park, North Carolina

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S. Trivikrama Rao Atmospheric Sciences Modeling Division, Air Resources Laboratory, National Oceanic and Atmospheric Administration, and U.S. Environmental Protection Agency, Research Triangle Park, North Carolina

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Print Publication:
01 Jul 2007
Collections:
NOAA/EPA Golden Jubilee
DOI:
https://doi.org/10.1175/JAM2523.1
Page(s):
994–1008
Restricted access

Abstract

Ozone is produced by chemical interactions involving nitrogen oxides (NO x ) and volatile organic compounds in the presence of sunlight. At high concentrations, ground-level ozone has been shown to be harmful to human health and to the environment. It has been recognized that ozone is a regional-scale problem and that regionwide control strategies would be needed to improve ozone air quality in the eastern United States. To mitigate interstate transport of ozone and its precursors, the U.S. Environmental Protection Agency issued a regional rule in 1998 known as the “NO x State Implementation Plan (SIP) Call,” requiring 21 states in the eastern United States to reduce their summertime NO x emissions by 30 May 2004. In this paper, the effectiveness of the new emission control measures mandated by the NO x SIP Call is assessed by quantifying the changes that occurred in the daily maximum 8-h ozone concentrations measured at nearly 50 locations, most of which are rural (33 sites of the Clean Air Status and Trend Network and 16 sites of the Air Quality System), over the eastern United States. Given the strong dependence of ozone formation and accumulation on meteorological conditions, the incidence of the latter is first mitigated, and meteorologically adjusted ozone concentrations are extracted using a multiple regression technique. By examining the differences between the cumulative distribution functions of the meteorologically adjusted ozone concentrations, it is shown that ozone concentrations in the eastern United States are now on average 13% less than those prior to the NO x SIP Call. Using back-trajectory analyses, it is also shown that emission controls on the electricity-generating units located in the Ohio River Valley have contributed toward the improvement of ozone air quality in downwind regions, especially east and northeast of the Ohio River Valley.

Corresponding author address: S. Trivikrama Rao, 109 T.W. Alexander Drive, Room E-240D, U.S. Environmental Protection Agency (MD - E243-02), Research Triangle Park, NC 27711. Email: rao.st@epa.gov; st.rao@noaa.gov

This article included in the NOAA/EPA Golden Jubilee special collection.

Abstract

Ozone is produced by chemical interactions involving nitrogen oxides (NO x ) and volatile organic compounds in the presence of sunlight. At high concentrations, ground-level ozone has been shown to be harmful to human health and to the environment. It has been recognized that ozone is a regional-scale problem and that regionwide control strategies would be needed to improve ozone air quality in the eastern United States. To mitigate interstate transport of ozone and its precursors, the U.S. Environmental Protection Agency issued a regional rule in 1998 known as the “NO x State Implementation Plan (SIP) Call,” requiring 21 states in the eastern United States to reduce their summertime NO x emissions by 30 May 2004. In this paper, the effectiveness of the new emission control measures mandated by the NO x SIP Call is assessed by quantifying the changes that occurred in the daily maximum 8-h ozone concentrations measured at nearly 50 locations, most of which are rural (33 sites of the Clean Air Status and Trend Network and 16 sites of the Air Quality System), over the eastern United States. Given the strong dependence of ozone formation and accumulation on meteorological conditions, the incidence of the latter is first mitigated, and meteorologically adjusted ozone concentrations are extracted using a multiple regression technique. By examining the differences between the cumulative distribution functions of the meteorologically adjusted ozone concentrations, it is shown that ozone concentrations in the eastern United States are now on average 13% less than those prior to the NO x SIP Call. Using back-trajectory analyses, it is also shown that emission controls on the electricity-generating units located in the Ohio River Valley have contributed toward the improvement of ozone air quality in downwind regions, especially east and northeast of the Ohio River Valley.

Corresponding author address: S. Trivikrama Rao, 109 T.W. Alexander Drive, Room E-240D, U.S. Environmental Protection Agency (MD - E243-02), Research Triangle Park, NC 27711. Email: rao.st@epa.gov; st.rao@noaa.gov

This article included in the NOAA/EPA Golden Jubilee special collection.

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Journal of Applied Meteorology and Climatology

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