Final answer:
Obstructions to visibility include smoke, haze, volcanic ash, and pollution causing particles like PM2.5. Weather conditions and air pollution significantly contribute to reduced visibility, impacting both on-ground views and astronomical observations.
Step-by-step explanation:
Some common obstructions to visibility include smoke, haze, volcanic ash, and other particulate matters. Factors that contribute to reduced visibility are often related to atmospheric conditions and pollution. Fine particles (PM2.5) are the main cause of visibility impairment, known as haze, affecting many regions including national parks and wilderness areas.
Weather conditions such as clouds, wind, and rain can significantly limit visibility, with some sites experiencing clear weather up to 75% of the time. In urban environments, air pollution, including smog which is a mix of pollutants like sulfur oxides (SOx), nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO₂), can obscure visibility. The nitrate particles resulting from NOx create a hazy atmosphere that makes it challenging to see, especially in many national parks that we visit for their scenic views.
Volatile organic compounds (VOCs), emissions from industrial facilities, motor vehicle exhaust, and natural sources such as volcanic eruptions also contribute to air pollution and visibility reduction. Not just in the lower atmosphere, visibility restrictions can also affect astronomical observations, where astronomers have identified scattering of light by particulate matter or 'bad seeing' due to turbulent air among the challenges for clear cosmic views.