If a great enough concentration of particles is present, they will darken the sky. How visibility is measured Until the early 1970s, AQMD officials measured visibility by standing on the roofs of air quality monitoring stations and comparing the furthest visible object with photographs of landmarks of known distance. On the worst days, pollution would drive visibility to less than one-half mile. AQMD now uses an instrument called a nephelometer to measure visibility. The nephelometer draws in an air sample and measures the amount of light scattering.
Visibility is calculated from that measurement.
Bad for health, too As bad as particulate pollution is for visibility, it has an even worse effect on human health. Numerous studies have linked particulate pollution to an increased number of emergency room visits, asthma attacks and premature deaths. Prognosis for future views Visibility in the region has gradually improved due to air pollution controls. By 2010, when all air quality standards are projected to be met, residents will enjoy clear views more frequently. In Long Beach, visibility is expected to increase from an average of about 10 miles today to 25 miles in 2010.