Because it is difficult to reduce this material to microscopic sizes, crustal material tends to be larger than other particles and tends to fall from the air sooner, contributing less to the overall effect of haze. A uniform haze degrades visibility evenly across the horizon and from the ground to a height well above the highest features of the landscape. Uniform haze often travels long distances and covers large geographic area, in which case it is called a regional haze. In a layered haze , you can see the top edge of the pollution layer. This is often the case when pollution is trapped near the ground beneath a temperature inversion.
Plumes result from local sources.
Plumes and plume-like layers of elevated pollution take their shape under certain meteorological condition where the air is stable or constrained. Some of the pollutants which form haze have been linked to serious health effects and environmental damage. Exposure to particles in the air have been linked with increased respiratory illness, decreased lung function, and premature death. In addition, sulfate and nitrate particles contribute to acid rain, which can damage forests, reduce fish populations, and erode buildings, historical monuments, and even car paint. To reduce haze we must reduce emissions of haze-forming pollutants across broad areas of the country.