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Variation of Visual Air Quality in the Paso del Norte Airshed

机译：Paso del Norte Airshed的视觉空气质量变化

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A decade long imaging program has documented the most frequently perceived form of air pollution in the Paso del Norte Airshed (PdNA). Light scattering and attenuation caused by fine particulate matter is sufficient to regularly obscure either the base, the ridge-top, or both, of 500-600 m bordering mountains at ranges of 2-4 km. A parallel Visual Air Quality (VAQ) recording system for the PdNA was set up by the Texas Natural Resource Conservation Commission (TNRCC) and predecessor agency. This system has taken 35mm transparency images three times a day, and continuous S-VHS Time-Lapse (4-sec) analog video through the decade of the 1990's. The present authors have developed a digital upgrade to the TNRCC video system that puts a continuous image stream and archived images at selected intervals on a web site (www.ozonemap.org/archives). The historical record of visual quality can be cost-effectively retrieved by quantitative analysis of digitized 35mm transparency images. Conversely, quantitative analysis of images from the "analog" video system over a period of years proved to be elusive because various age and environmental factors introduced noise into the images that reduced contrast (i.e., ridge edge vs. sky). We report VAQ factors obtained by direct comparison of Contrast Ratios (specific targets) and Contrast Variance (image zones) in the current "digital" video record and the digitized 35 mm archive slides. The period 1991-1999 results of the Contrast Ratio and Contrast Variance analysis in urban parts and mountain ridge parts of the PdNA vary from a normalized 100% to less than 15% for all targets and zones evaluated at midmoming (nominally 9 o'clock MST).
机译：十年长成像程序记录了空气污染的最经常感知形式在帕索城北空气流域（PDNA）。光散射和衰减引起的细颗粒物是足以在2-4公里范围定期掩盖任一所述基座，所述脊顶，或两者，500-600米接壤山脉。对于质粒DNA的并行视觉空气质量（VAQ）记录系统是由得克萨斯州自然资源保护委员会（TNRCC）和前身机构成立。该系统用了35毫米透明度图像的一天三次，和连续的S-VHS时间流逝（4-仲丁基）至20世纪90个年代的十年模拟视频。本文作者开发了数字化升级到TNRCC视频的制度，使连续的图像流，并在一个网站上（www.ozonemap.org/archives）选定的时间间隔存档图像。视觉质量的历史记录可以低成本地通过数字化35毫米透明图像的定量分析检索是。反之，从“类似物”视频系统在一段年图像的定量分析证明是难以实现的，因为各种年龄和环境因素的噪声引入的图像，对比度降低（即，脊缘与天空）。我们报告VAQ因素在当前“数字化”录像对比度的直接比较（具体目标）和对比度差异（图像区域）获得和数字化35毫米存档幻灯片。期间1991至1999年的结果在城市部分和PDNA的山脊份对比度和对比度方差分析的从归一化100％变化至小于15％在midmoming（标称9时MST评价所有的目标和区域）。

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