Simulation of boundary layer trajectory dispersion sensitivity to soil moisture conditions: MM5 and Noah-based investigation Arturo I. Quintanar b, c, * , Rezaul Mahmood a, b, c , Monica V. Motley b, c , Jun Yan b , John Loughrin d , Nanh Lovanh d a Meteorology Program, Western Kentucky University, College Heights Blvd., Bowling Green, KY 42101, USA b Department of Geography and Geology, Western Kentucky University, College Heights Blvd., Bowling Green, KY 42101, USA c Kentucky Climate Center, Western Kentucky University, College Heights Blvd., Bowling Green, KY 42101, USA d Agricultural Research Service, Animal Waste Management Research Unit, USDA, 230 Bennett Lane, Bowling Green, KY 42101, USA article info Article history: Received 20 May 2008 Received in revised form 1 April 2009 Accepted 2 April 2009 Keywords: MM5 HYSPLIT Soil moisture Wind trajectory Air quality abstract In this study, the sensitivity of trajectory paths to anomalous soil moisture was analyzed during three different synoptic episodes in June 2006. The MM5 and Noah land surface models were used to simulate the response of the planetary boundary layer. The HYSPLIT model was used for trajectory analysis. It was found that the response in horizontal lower-level wind field was larger at regions where vertical wind velocity changes were also large. In addition, the sensitivity to soil moisture changes was significant and localized where convective activity was well developed and synoptic effects did not dominate. A non- local effect was felt over the rest of the domain where convection was not present since the model atmosphere reacted as a whole to compensate for induced changes in vertical velocity. This finding was supported by the fact that domain averaged vertical velocities changes were of the order of 0.2 cm s 1 or less at about 650 hPa and about 200 times smaller than modeled local vertical velocity changes. The largest change in horizontal wind field near the surface was found for weak synoptic events on June 11– 12 and June 22–23 while the stronger synoptic event of June 17–18 showed smaller differences. These changes in wind field conditions impacted the transport and dispersion of pollutants. To quantify the sensitivity of air quality estimates to soil moisture uncertainty, we have used three well known measures of trajectory differences: the absolute horizontal transport deviation (AHTD), the relative horizontal transport deviation (RHTD) and the absolute vertical transport deviation (AVTD) for an ensemble of 98 trajectories departing from a region well within the computational domain. For the June 11–12 event it was found that for wet and dry soil moisture experiments, AHTD, RHTD, and AVGTD can reach values in the range 60–100 km,10–20% and 500–900 m at 24 h run time, respectively. For the June 17–18 and June 22–23 events these values of trajectory differences were reduced more than half. These differences in behavior between time periods are largely attributed to the combined effects of synoptic forcing and the sensitivity of planetary boundary layer to soil moisture changes during well developed convection. The implication for air quality studies is that the soil moisture anomaly and related uncertainty in planetary boundary layer response needs to be incorporated in order to construct an ensemble of the most probable scenarios in which pollutants are released and transported throughout a given target region. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Emissions from agricultural and animal operations directly impact the quality of life and health of people that live and work in proximity to these sites. One example is the so called Concentrated Animal Feeding Operations (CAFOS) which are sources of malodorous gases and particulate emissions. They may be an important health concern as they can be transported very effi- ciently over several kilometers and affect nearby communities (Janni, 1982; Gassman, 1993; Wang et al., 2006). Concentrations of pollutants emitted from sources such as CAFOS can be modeled using a transport and diffusion equation in an Eulerian framework. The advantage with this approach is that complex emission and chemistry scenarios can be considered although its accuracy and usefulness is severely limited by spatial * Corresponding author at: Department of Geography and Geology, Western Kentucky University, College Heights Blvd., Bowling Green, KY 42101, USA. Tel.: þ1 (270) 745 2634; fax: þ1 (270) 745 6410. E-mail address: arturo.quintanar@wku.edu (A.I. Quintanar). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.04.005 Atmospheric Environment 43 (2009) 3774–3785