Atmospheric Environment 40 (2006) 5097–5109 Plume-in-grid modeling of summer air pollution in Central California Krish Vijayaraghavan à , Prakash Karamchandani, Christian Seigneur Atmospheric & Environmental Research, Inc., 2682 Bishop Drive, Suite 120, San Ramon, CA 94583, USA Received 30 March 2005; received in revised form 28 December 2005; accepted 28 December 2005 Abstract CMAQ-APT (Community Multiscale Air Quality model with ‘‘Advanced Plume Treatment’’), a state-of-the-science implementation of sub-grid scale reactive plumes in CMAQ, was used to simulate ozone (O 3 ) and nitric acid (HNO 3 ) formation during a 4-day July/August 2000 episode in central California. The top ten NO x emitting plants in the Central California Ozone Study (CCOS) domain were selected for explicit plume treatment. The VOC- vs. NO x -limited nature of the background environment, as determined from air quality data in different parts of the CCOS domain, was used to understand the differences in ozone production and destruction between the APT and base results. Use of the plume-in- grid treatment results in up to 10 ppb less O 3 than the base under some O 3 production conditions and up to 6 ppb higher O 3 under others. Over most of the areas impacted by the top ten NO x emitting plants, the surface HNO 3 concentrations in the APT simulation are about 0.1–1 ppb (1–25%) lower than those in the base simulation. The low NO x emissions from point sources in central California explain these results. r 2006 Elsevier Ltd. All rights reserved. Keywords: Air quality model; Sub-grid; Ozone; Nitric acid; VOC- vs. NO x -limited 1. Introduction The limitations of conventional implementations of the sub-grid scale treatment of plumes in 3-D air quality models have been listed by Karamchandani et al. (2002), who described the development and application of a new state-of-the-science plume-in- grid (PinG) air quality model that provides a more realistic representation of the behavior of reactive plumes in the atmosphere. This model consists of a reactive plume model, SCICHEM (Karamchandani et al., 2000a), embedded into the 3-D Community Multiscale Air Quality (CMAQ) model (Byun and Ching, 1999) and is referred to as CMAQ-APT (CMAQ with Advanced Plume Treatment). An early version of CMAQ-APT was applied to explicitly simulate the plumes from two power plants for a 5-day ozone (O 3 ) episode in the Nashville/western Tennessee area (Karamchandani et al., 2000b). An improved version of the model was later used for the 30 largest NO x point sources in the eastern US for a 5-day episode in 1995 (Karamchandani et al., 2002). CMAQ-APT has been updated here to incorporate updates in the latest releases of CMAQ (version 4.3) and SCICHEM (version 1601). We describe the ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.12.050 à Corresponding author. Tel.: +1 925 244 7127; fax: +1 925 244 7129. E-mail address: krish@aer.com (K. Vijayaraghavan).