GEGO, E., P. PORTER, A. GILLILAND, AND S. RAO. OBSERVATION-BASED ASSESSMENT OF THE IMPACT OF NITROGEN OXIDES EMISSIONS REDUCTIONS ON OZONE AIR QUALITY OVER THE EASTERN UNITED STATES. JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY. American Meteorological Society, Boston, MA, 46(7):994-1008, (2007).
Ozone is produced by chemical interactions involving nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs) in the presence of sunlight. At high concentrations, ground-level ozone has been shown to be harmful to human health and the environment. It has been recognized that ozone is a regional-scale problem and region-wide control strategies would be needed to improve ozone air quality in the eastern United States. To mitigate inter-state transport of ozone and its precursors, the U.S. Environmental Protection Agency issued a regional rule in 1998 known as the 'NOx SIP Call', requiring 21 states in the eastern United States to reduce their summertime NOx emissions by May 30, 2004. In this paper, we assess the effectiveness of the new emission control measures mandated by the NOx SIP call by quantifying the changes that occurred in the daily maximum 8-hr ozone concentrations measured at nearly fifty locations, mostly 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, we first mitigate the incidence of the latter and extract meteorologically-adjusted ozone concentrations using a multiple regression technique. By examining the differences between the cumulative distribution functions of the meteorologically-adjusted ozone concentrations, we show that ozone concentrations in the eastern U.S. are now on average 13% less than prior to the NOx SIP call. Using back-trajectory analyses, we also show that emission controls on the electric 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.
This team's objective is to research and develop analytical tools that will quantify the effect of regional NOx emission reductions on ambient air quality, thus providing a measure of control stategy accountability.