Cabrera H, Dawson S V, Stromberg C
Research Division, California Air Resources Board, Sacramento, California 95812, USA.
Environ Pollut. 1988;53(1-4):397-408. doi: 10.1016/0269-7491(88)90049-8.
Evidence shows that the current national primary ambient air quality standard, if attained, would still permit substantial injury to vegetation. Thus, in March 1987, the California Air Resources Board (CARB) began consideration of the evidence for the effects of ozone (O3) on vegetation, and of several possible state ambient air quality standards designed to protect vegetation, especially crops, from O3 injury. In its review, the CARB addressed a number of issues relevant to such a standard. One issue considered by the CARB is the relationship of an ambient air quality standard to natural background levels of O3, which would greatly influence the practicality of attainment. Attainment of a standard close to natural background could entail excessive costs. Another issue considered is the occurrence of oxidants other than O3 that can damage vegetation. Throughout much of California, O3 accounts for over 90% of the oxidant air pollutants, and the CARB considered whether, in keeping with current practice, O3 should be used as a surrogate for total oxidant air pollutants. A major new piece of information presented to the CARB was an assessment of the economic effects of several potential standards. This assessment, produced by University of California scientists at Riverside and Davis, calculated the benefits of the potential standards in comparison to current O3 levels and estimated natural O3 background. This assessment was developed using field chamber response data, local crop data, and local O3 concentration data as inputs to the California Agricultural Resources Model, which accounts for both supply and demand effects. Because of California's varied climate, agricultural production occurs on a year-round basis, with overlapping growing seasons for many crops. Over long periods of time, O3 levels may vary markedly because of the influence of various factors, and a 1-h standard may not be an accurate indicator of growing season O3 exposure. A moving three-month averaging time has been proposed as a way to approximate the growing seasons of California's 200 crops. However, a sufficiently stringent 1-h standard would serve as a surrogate for a growing season standard. The CARB reviewed evidence supporting both long-term and short-term standards. Agriculture dominates the economies of some regions within California but is a minor components of other regional economies. Because the San Joaquin Valley is California's most important agricultural area, the CARB reviewed evidence for a regional standard for this area that would be more stringent than standards for other parts of the state.
有证据表明，现行的国家一级环境空气质量标准即便得以实现，仍会对植被造成严重损害。因此，1987年3月，加利福尼亚空气资源委员会（CARB）开始审视有关臭氧（O₃）对植被影响的证据，以及旨在保护植被（尤其是农作物）免受O₃损害的若干可能的州环境空气质量标准。在审查过程中，CARB探讨了许多与此类标准相关的问题。CARB审议的一个问题是环境空气质量标准与O₃自然背景水平的关系，这将极大地影响达标可行性。接近自然背景的标准的实现可能会带来过高成本。另一个审议的问题是除O₃之外会损害植被的氧化剂的存在情况。在加利福尼亚大部分地区，O₃占氧化剂空气污染物的90%以上，CARB考虑按照当前做法，是否应将O₃用作总氧化剂空气污染物的替代物。提交给CARB的一项重要新信息是对若干潜在标准的经济影响的评估。这项由加利福尼亚大学河滨分校和戴维斯分校的科学家进行的评估，计算了与当前O₃水平及估计的自然O₃背景相比，潜在标准的益处。该评估利用田间试验箱响应数据、当地作物数据和当地O₃浓度数据作为输入，纳入了供求影响的加利福尼亚农业资源模型。由于加利福尼亚气候多样，农业生产全年都有，许多作物的生长季节相互重叠。从长期来看，由于各种因素的影响，O₃水平可能会有显著变化，1小时标准可能无法准确反映生长季节的O₃暴露情况。有人提议采用三个月移动平均时间来近似加利福尼亚200种作物的生长季节。然而，足够严格的1小时标准可作为生长季节标准的替代物。CARB审查了支持长期和短期标准的证据。农业在加利福尼亚州一些地区的经济中占主导地位，但在其他地区经济中只是一个次要组成部分。由于圣华金河谷是加利福尼亚最重要的农业区，CARB审查了该地区比该州其他地区标准更严格的区域标准的证据。
