| Many pesticides have been identified as persistent, bio-accumulative, and toxic pollutants. Concerns about their adverse effects on the environment have been expressed for many years. Due to applications in the past, significant pesticide residues remain in the soil. These residues can result in significant pesticide emissions into the atmosphere, where pesticides can be transported over long distances and deposited far from where they were originally applied.; To investigate issues related to pesticides in the environment, this project has developed a 3-D Eulerian multimedia regional fate and chemical transport modelling system based on the US EPA MM5/MCIP/SMOKE/CMAQ air quality modelling system, which this project has coupled to PEM, a dynamic pesticide emission model. This study has, to our knowledge for the first time, incorporated the Koa gas-particle partitioning model into Models-3/CMAQ for the semi-volatile behaviour of pollutants. The modelling package takes into account the important physical and chemical processes and factors, from sources to sinks, related to pesticides in both the atmosphere and the soil, including pesticide application modes, soil types, soil tilling, growing stages of crops, advection and diffusion in the soil, emission, partitioning, transport in the atmosphere, chemical transformation, dry deposition, and wet deposition. Moreover, this modelling system models pesticides along with other atmospheric compounds (e.g. O 3, OH radicals, NO3 radicals, and particulate materials) simultaneously and addresses chemical and physical interactions among all these pollutants, including pesticides.; This project has used the modelling system to study the environmental behaviour of toxaphene, a persistent, bio-accumulative, and toxic pesticide. The study was carried out for a 11/2 year period from January 1, 2000 to June 30, 2001 and covers a domain that includes most of North America with a resolution of 36x36 km. Comparisons of the modeled results with measured or estimated values show good agreement. The comparisons include (i) comparison of modeled daily-average toxaphene air concentrations against measurements; (ii) comparison of toxaphene fraction on particle phase over that of all phases against estimate as well as measurements; (iii) comparison of modeled annual wet deposition against measurements; (iv) comparison of modeled annual dry deposition against estimate; (v) and comparisons of surface temperatures and soil moistures predicted by MM5 and PEM. The comparison of modeled daily-average air concentrations against measurements was conducted at five measuring sites for the year 2000. To our knowledge, this is the first attempt to establish the relationship between modeled daily-average pesticide air concentrations and measurements at so many locations and for such a long period. The good agreement of these comparisons shows that the modelling system has the ability to simulate emissions, air concentrations in gas phase and particle phase, dry deposition, and wet deposition, which are determined by simulation of the important physical and chemical processes in the atmosphere and the soil, as well as agricultural practices and meteorology.; This work has estimated a toxaphene residue inventory for Mexico, and has converted the U.S. residue inventory, obtained from Environment Canada, from Latitude-Longitude projection to Lambert projection. Although this study has found anomalous residues around the Texas site in the U.S. residue inventory, data analyses imply that the inventories are generally reasonable.; This project has used the merged Mexican and U.S. residue inventory and coupled MM5-PEM to develop an hourly and gridded toxaphene emission inventory for a period from January 1, 2000 to June 30, 2001. To our knowledge, this is the first such gridded and hourly toxaphene emission inventory developed for North America. The spatial distribution of simulated emissions in the domain is consistent with... |
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