The kind of haziness you refer to requires water to condense into tiny droplets - so a relative a relative humidity near 100 percent is usually required. The other important variable is the presence of condensation nuclei for droplets to form. Haziness is a complex interplay of these two quantities. Here in the northeast (RI) we seldom get haziness unless there is a strong inversion layer (warm air overlying cooler air) that limits convection and traps water vapor and condensation nuclei in a shallow layer. Houston and coastal Florida are other good examples of humidity haze. A notable exception was this weekend where lots of condensation nuclei were drifting down to RI from the wildfires in Montreal - causing extreme haze (1/2 mile visibility) even though the relative humidity was only around 70 percent (although there was an inversion around 3-4000 ft throughout most of the day).
Haziness in the dry southwest can be caused by scattering from power plant pollutants (e.g., Grand Canyon) or aerosols from pine trees (e.g., Lake Tahoe).
Bob at PC
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From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of curtis osterhoudt [flutzpah@yahoo.com]
Sent: Monday, May 31, 2010 7:17 PM
To: Forum for Physics Educators
Subject: [Phys-l] Humidity and visibility
What is it that affects visibility ("haziness") more: relative or absolute humidity? Perhaps neither one, since it's (probably) Mie scattering, and that's dependent on much more than a single number. Thoughts?
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As a species, we are forever sticking our fingers into the electric socket of the Universe to see what'll happen next. It's a trait that'll either save us or kill us, but by god it's what makes us human beings. I'd rather be in the company of people who look at Mars than people who contemplate humanity's navel -- other worlds are better than fluff. ~~Sir Terence David John Pratchett
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