Background on Haze

What is haze?

Regional haze pollution, mainly in the form of sulfate, organic and nitrate fine particles, results in poor visibility from mountain tops as well as negative human health impacts. Haze is composed of very small fine particles, smaller than 2.5 micrometers (µm) (over 20 times smaller in diameter than a human hair) that are suspended in the air. These particles originate from a variety of sources, some natural, but much of it originates from power plant and automobile emissions. Haze is generally composed of 5 major components: sulfate aerosol, nitrate aerosol, organic carbon aerosol, elemental carbon, and dust from the earth's crust.

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The gauge above is based on the IMPROVE equation for estimating visibility. The IMPROVE method uses measured concentrations of each component of haze (sulfate, nitrate etc) and multiplies the concentrations by light extinction factors. The light extinction cause by each component is totaled and can be converted into visual range. The more light extinction, the lower the visual range.

Relative humidity plays a role in reducing visibility only when these particles are present. Try putting all concentrations to zero and then move relative humidity up and down. Does it change visual range? Now put sulfate up to 1 ug/m3 and adjust humidity. Is there a difference?

What do these different visual range values actually look like? Go to our Visibility Conditions page to see some examples.

Learn more about AMC's active campaign for a strong Regional Haze program by joining our Conservation Action Network and reading our recent White Paper.