tailieunhanh - Pesticides in the AtmosphereDistribution, Trends, and Governing Factors - Chapter 5

Tổng quan về phân phối quốc gia và xu hướng của thuốc trừ sâu trong khí quyển, và các yếu tố chi phối làm ảnh hưởng đến nồng độ trong khí quyển, để lại nhiều câu hỏi cụ thể chưa có ai trả lời. Mặc dù một số vấn đề không thể được giải quyết trên cơ sở thông tin hiện có, các chủ đề quan trọng nhất xứng đáng với nỗ lực của chúng tôi tốt nhất. Ba chương sau đây thảo luận chi tiết các chủ đề quan trọng của nguồn và vận chuyển giai đoạn, tài sản,. | CHAPTER 5 Analysis of Key Topics Sources and Transport The overview of the national distribution and trends of pesticides in the atmosphere and the governing factors that affect their concenttations in the atmosphere leaves many specific questions unanswered. Although some issues cannot be addressed on the basis of existing information the most important topics deserve our best attempt. The following three chapters discuss in detail the key topics of sources and ttansport phases properties and transformations and environmental significance of pesticides in the atmosphere. SEASONAL AND LOCAL USE PATTERNS The overwhelming conclusions drawn from reviewing the studies listed in Tables and are that the highest pesticide concentrations in air and rain are correlated to local use and that locally high concentrations in rain and air are very seasonal. The highest concentrations usually occur in the spring and summer months coinciding with application times and warmer temperatures. Insecticide concentrations in air and rain however are also high during the autumn and winter in correspondence to local use. Nations and Hallberg 1992 detected clear areal and seasonal trends in herbicide detections in Iowa rain. The herbicides pendimethalin EPTC and propachlor were detected more frequently in the western part of the state where they were used more heavily than in the eastern part. The same ttend was found for atrazine alachlor and cyanazine which were used more in the northeastern part of the state. Pesticide detections in rain generally began in late April and continued through July or August. Concenttations were highest during April May and June the months during which most of the pesticides are applied in Iowa. From August through November pesticide detection frequency and concentrations in rain were much less with no pesticide detections in December through March see Figure . Pesticides were detected earliest in southern parts of Iowa where spring .