Atmospheric Environment 38 (2004) 4969–4974 Technical Note Observed and modeled VOC chemistry under high VOC/NO x conditions in the Southeast United States national parks Daiwen Kang a,Ã , Viney P. Aneja a , Rohit Mathur b,1 , John D. Ray c a Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695-8208, USA b Carolina Environmental Program, University of North Carolina, Chapel Hill, NC 27599-1105, USA c Air Resources Division, National Park Service, Denver, CO 80225-0287, USA Received 5 November 2003; accepted 21 May 2004 Abstract In airsheds that contain high volatile organic compounds (VOCs) and low NO x (=NO+NO 2 ) concentrations, ozone (O 3 ) production may be significantly suppressed by NO x reactions that lead to the formation of organic nitrates. O 3 and its precursors (VOCs and NO x ) ambient levels simulated using a regional-scale photochemical model, called Multiscale Air Quality Simulation Platform, are analyzed and compared to observed data from three southeast United States national parks. r 2004 Elsevier Ltd. All rights reserved. Keywords: VOCs; Ozone; Atmospheric chemistry; Air quality modeling 1. Introduction High ozone (O 3 ) concentrations are attributed to the oxidation of NO x with the presence of excessive amounts of biogenically emitted Volatile Organic Compounds(VOCs) such as isoprene (Chameides et al., 1988; Trainer et al., 1987) in the southeast US rural areas during summer (Chameides et al., 1997; Heck et al., 1984). The new 8-h O 3 National Ambient Air Quality Standard (NAAQS) (0.085ppmv) is likely to bring even more suburban and rural locations into noncompliance (Chameides et al., 1997). Biogenic VOCs emitted by vegetation (Fehsenfeld et al., 1992; Lamb et al., 1993; Fuents et al., 2000) and anthropogenic VOCs emitted by human activities are both widely present in the rural areas (Hagerman et al., 1997; Kang et al., 2001). Previous studies indicate that the influence of these VOCs on O 3 production can be significant (Trainer et al., 1987; Liu et al., 1987; Geron et al., 1994). Recent studies indicate that the VOC emission rates used in the current air quality models (Kang et al., 2003; Palmer et al., 2003) for developing control strategies may be low by a factor of 2 to 10. The O 3 -production mechanism in the literature is often illustrated using O 3 isopleths (Dodge, 1977). When the ratios of nonmethane hydrocarbons (NMHCs) to NO x are larger than 15:1 in the Empirical Kinetic- Modeling Approach (EKMA), the maximum O 3 con- centration is not very sensitive to the hydrocarbon concentrations. In general, the current understanding is that under non-NO x -limited conditions with the increase ARTICLE IN PRESS www.elsevier.com/locate/atmosenv AE International – North America 1352-2310/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.05.054 Ã Corresponding author. Atmospheric Modeling Division, US EPA, Mail Drop E243-01, RTP, NC 27711. Tel.: +1-919- 541-2460. E-mail address: kang.daiwen@epamail.epa.gov (D. Kang). 1 Present address: Atmospheric Modeling Division, US EPA, Mail Drop E243-03, RTP, NC 27711, USA.