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Visibility and Regional Haze

Visibility and Regional Haze. Aerosol Scattering and Visibility Loss Regional Haze Visibility Pattern and Trends Resource Links. Contact: Rudolf Husar, rhusar@mecf.wustl.edu. Aerosol Scattering and Visibility Loss.

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Visibility and Regional Haze

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  1. Visibility and Regional Haze Aerosol Scattering and Visibility Loss Regional Haze Visibility Pattern and Trends Resource Links Contact: Rudolf Husar, rhusar@mecf.wustl.edu

  2. Aerosol Scattering and Visibility Loss • The reduction of visual range is the most noticeable effect of PM2.5 particles. • The cause of visibility loss is light scattering and absorption by particles in the optically active size range between 0.3 and 1.0 m. • Sulfates and organics are the main contributors to light extinction, but in some regions nitrates and dust are also significant. • At the limit of visual range, the contrast between the visual target and the horizon sky is below the human detection limit of about 5%.

  3. Regional Haze • Regional haze arises when the contributions of many individual sources are mixed together during long range transport. • The resulting spatially uniform hazy airmasses can cover multi-state areas in excess of 1000 km in size. • Regional haze episodes are most prevalent during the summer in the Eastern US, when stagnating high pressure systems cause the regional accumulation of many pollutants including PM2.5. • Over the Southwest, regional haze events can significantly deteriorate the vistas in National Parks and Wilderness Areas.

  4. Visibility Pattern and Trends • In the Eastern US, throughout the 1980s, the 75th percentile BEXT exceeded 0.15 km-1 (visibility < 10 miles). • Most notable are the hazy regions on both sides of the Appalachian Mountains where the BEXT exceeded 0.2 km-1. • Since the early 1980s, haziness has decreased 10-15% throughout the Eastern US.

  5. Resource Links • Workbook Table of Contents • Comment and Feedback Page • Applications / Reports • Data sets used in the Applications • Methods and tools used in the Applications

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