a Cooperative Institute for Research in the Atmosphere , Colorado State University , Fort Collins , CO , USA.
b Air Resources Division , National Park Service , Lakewood , CO , USA.
J Air Waste Manag Assoc. 2019 Feb;69(2):145-161. doi: 10.1080/10962247.2018.1506370. Epub 2018 Dec 6.
Several studies have been carried out over the past 20 or so years to assess the level of visual air quality that is judged to be acceptable in urban settings. Groups of individuals were shown slides or computer-projected scenes under a variety of haze conditions and asked to judge whether each image represented acceptable visual air quality. The goal was to assess the level of haziness found to be acceptable for purposes of setting an urban visibility regulatory standard. More recently, similar studies were carried out in Beijing, China, and the more pristine Grand Canyon National Park and Great Gulf Wilderness. The studies clearly showed that when preference ratings were compared to measures of atmospheric haze such as atmospheric extinction, visual range, or deciview (dv), there was not a single indicator that represented acceptable levels of visual air quality for the varied urban or more remote settings. For instance, using a Washington, D.C., setting, 50% of the observers rated the landscape feature as not having acceptable visual air quality at an extinction of 0.19 km (21 km visual range, 29 dv), while the 50% acceptability point for a Denver, Colorado, setting was 0.075 km (52 km visual range, 20 dv) and for the Grand Canyon it was 0.023 km (170 km visual range, 7 dv). Over the past three or four decades, many scene-specific visibility indices have been put forth as potential indicators of visibility levels as perceived by human observers. They include, but are not limited to, color and achromatic contrast of single landscape features, average and equivalent contrast of the entire image, edge detection algorithms such as the Sobel index, and just-noticeable difference or change indexes. This paper explores various scene-specific visual air quality indices and examines their applicability for use in quantifying visibility preference levels and judgments of visual air quality. Implications: Visibility acceptability studies clearly show that visibility become more unacceptable as haze increases. However, there are large variations in the preference levels for different scenes when universal haze indicators, such as atmospheric extinction, are used. This variability is significantly reduced when the sky-landscape contrast of the more distant landscape features in the observed scene is used. Analysis suggest that about 50% of individuals would find the visibility unacceptable if at any time the more distant landscape features nearly disappear, that is, they are at the visual range. This common metric could form the basis for setting an urban visibility standard.
过去 20 多年来，已经进行了多项研究，以评估城市环境中被认为可接受的视觉空气质量水平。将幻灯片或计算机投影的场景展示给几组人，并要求他们判断每张图像是否代表可接受的视觉空气质量。目标是评估为制定城市能见度监管标准而发现的可接受的浑浊度水平。最近，在中国北京、更原始的大峡谷国家公园和大湾荒野进行了类似的研究。这些研究清楚地表明，当将偏好等级与大气浑浊度的测量值（如大气消光、能见度或分视值 (dv)）进行比较时，没有一个单一的指标能够代表不同城市或更偏远环境的可接受的视觉空气质量水平。例如，以华盛顿特区为例，有 50%的观察者认为在消光度为 0.19 公里（21 公里能见度，29 dv）的情况下，景观特征没有可接受的视觉空气质量，而在科罗拉多州丹佛市的 50%可接受点为 0.075 公里（52 公里能见度，20 dv），在大峡谷则为 0.023 公里（170 公里能见度，7 dv）。在过去的三、四十年中，已经提出了许多特定场景的能见度指数，作为人类观察者感知的可见度水平的潜在指标。它们包括但不限于单个景观特征的颜色和非彩色对比度、整个图像的平均和等效对比度、边缘检测算法（如 Sobel 指数）以及刚刚可察觉的差异或变化指数。本文探讨了各种特定场景的视觉空气质量指数，并研究了它们在量化可见度偏好水平和视觉空气质量判断方面的适用性。 影响：可见度可接受性研究清楚地表明，随着烟雾的增加，可见度变得越来越不可接受。然而，当使用大气消光等通用烟雾指标时，不同场景的偏好水平存在很大差异。当使用观察场景中较远距离景观特征的天空-景观对比度时，这种可变性会显著降低。分析表明，如果任何时候较远距离的景观特征几乎消失，即它们处于可见度范围内，那么大约有 50%的人会发现能见度不可接受。这个通用指标可以作为制定城市可见度标准的基础。
