Plume Dispersion in Four Pine Thinning Scenarios: Development of a Simple Pheromone Dispersion Model

A unique field campaign was conducted in 2004 to examine how changes in stand density may affect dispersion of insect pheromones in forest canopies. Over a 14-day period, 126 tracer tests were performed, and conditions ranged from an unthinned loblolly pine (Pinus taeda) canopy through a series of thinning scenarios with basal areas of 32.1, 23.0, and 16.1 m2ha-1. In this paper, one case study was used to visualize the nature of winds and plume diffusion. Also, a simple empirical model was developed to estimate maximum average concentration as a function of downwind distance, travel time, wind speed, and turbulence statistics at the source location. Predicted concentrations from the model were within a factor of 3 for 82.1 percent and 88.1 percent of the observed concentrations at downwind distances of 5 and 10 m, respectively. In addition, the model was used to generate a field chart to predict optimum spacing in arrays of anti-aggregation pheromone dispensers

A Tracer Investigation of Pheromone Dispersion in Lodgepole and Ponderosa Pine Forest Canopies

Tracer experiments were conducted in 2000 and 2001 to study spread of insect pheromone plumes in forest canopies. The field sites consisted of lodgepole pine (Pinus contorta) and ponderosa pine (P. ponderosa) canopies in 2000 and 2001, respectively. Ranges of temperature, wind speed, and turbulence conditions were similar in the two campaigns, and field data showed comparable variability on near-instantaneous time scales of wind speed, wind direction, and plume behavior. We developed simple empirical equations to estimate average horizontal and vertical plume spread as functions of standard turbulence statistics, downwind distance from the source, and wind speed. For horizontal plume spread, predicted dispersion coefficients were within a factor of 3, or better, for 97 percent of the observed values in the combined dataset from 2000 and 2001. Likewise, 99 percent of the predicted vertical dispersion coefficients were within a factor of 3 of the observed data

SPRAYTRAN 1.0 User’s Guide: A GIS-Based Atmospheric Spray Droplet Dispersion Modeling System

SPRAY TRANsport (SPRAYTRAN) is a comprehensive dispersion modeling system that is used to simulate the offsite drift of pesticides from spray applications. SPRAYTRAN functions as a console application within Environmental System Research Institute’s ArcMap Geographic Information System (Version 9.x) and integrates the widely-used, U.S. Environmental Protection Agency (EPA)-approved CALifornia PUFF (CALPUFF) dispersion model and model components to simulate longer-range transport and diffusion in variable terrain and spatially/temporally varying meteorological (e.g., wind) fields. Area sources, which are used to define spray blocks in SPRAYTRAN, are initialized using output files generated from a separate aerial-spray-application model called AGDISP (AGricultural DISPersal). The AGDISP model is used for estimating the amount of pesticide deposited to the spray block based on spraying characteristics (e.g., pesticide type, spray nozzles, and aircraft type) and then simulating the near-field (less than 300-m) drift from a single pesticide application. The fraction of pesticide remaining airborne from the AGDISP near-field simulation is then used by SPRAYTRAN for simulating longer-range (greater than 300 m) drift and deposition of the pesticide

Initial laboratory measurements of the evaporation rate of droplets inside a spray cloud

This article calculates the evaporation rate of water droplets stacked on several threads, positioned downwind of one another. The measurement approach was used previously to determine the evaporation rate of isolated suspended droplets, on a single thread, for development of the Spray Drift Task Force (SDTF) droplet evaporation data base. Here, the effect of evaporating droplets upwind of other droplets is examined, recovering the effective evaporation rate of individual water droplets surrounded by other water droplets in a spray cloud. The results quantify the modified wet bulb temperature depression felt by the droplets within the cloud and are used to compare AGDISP model predictions with SDTF aerial deposition data

Predicted deposition variability due to fluctuations in release height and drop size distribution

An extensive field study has been undertaken to quantify the aerial release of spray material through the changes in meteorology as the day progresses. An important subset of these collected data is one-second interval data of the aircraft behavior and the mechanical release systems. These unique data provide an excellent source of information on bounding the variability in the expected deposition patterns, and how this variability might impact any error bounds established around the time-averaged predictions generated by the AGDISP model. This paper quantifies the variability in aerial application parameters and makes suggestions with regard to possible implications of this variability on the variability of deposition predictions in the flight line direction

Predicted deposition variability due to fluctuatioins in release height and drop size distribution

An extensive field study has been undertaken to quantify the aerial release of spray material through the changes in meteorology as the day progresses. An important subset of these collected data is one-second interval data of the aircraft behavior and the mechanical release systems. These unique data provide an excellent source of information on bounding the variability in the expected deposition patterns, and how this variability might impact any error bounds established around the time-averaged predictions generated by the AGDISP model. This paper quantifies the variability in aerial application parameters and makes suggestions with regard to possible implications of this variability on the variability of deposition predictions in the flight line direction