Smelling Rain and Seeing the Leonid Meteor Shower

Q: Why does it smell so nice those first few minutes just when it starts to rain?
Susan K. and her father, Ron, Albuquerque, New Mexico

A: What a delightful question! Several things cause the good smell of rain--but the main one is humidity. Much water exists in the air just before it rains. That moisture makes plants release aromas so there are more scents in the air both immediately before and during rains. Also your nose functions better when cleaned by moist air so you notice more.

This is our present knowledge. Now let's speculate on some causes. I asked scientists around the world.

Ken Doxtader, professor of soils and crop science at Colorado State University, says that soil contains bacteria that make aromatic gas. When you dig in soil, you disturb the gas and free its aroma. Likewise when it rains. The rain floods the space between soil particles, displacing the bacteria's gas, and you smell an earthy fragrance.

Cloud water droplets form around tiny airborne clay particles. Steve Goodwin with NASA's Lightning and Atmospheric Research thinks downdrafts associated with rainstorms can bring those clay particles close to your nose and you may notice an earth scent,.

The breezes and winds that swirl rain also stir up smells around you--plants, soil, gases--so you notice them, says Robin Hicks of Melbourne, Australia's Bureau of Meteorology.

J. Hallet at the Desert Research Institute mentions how even surface bugs release odors when they get wet.

Q: Why does rain stop smelling so good as it rains longer?
Susan K. and her father, Ron, Albuquerque, New Mexico

A: When an odor molecule reaches a nerve hair on the smell lining in the nose, it fills a spot there. If the smell is strong (i.e., many molecules), soon all the hairs that respond to that particular odor are filled. Those receptor hairs have sent their smell messages to the brain and cannot send more until they detatch their present odor chemicals. So the receptors are quiet and the brain no longer perceives that smell. That is why you quit noticing the good smell of rain.

Q: Which day (18 or 19 November) will I be able to see a good meteor shower from Mumbai, India?
"About meteor shower", Mumbai, India

A: You can see the shower in Mumbai, India at its peak about 4 am, your time on Nov. 19, 2007. You're lucky, because the moon sets a little after midnight, so the skies should be dark — at least out in the country. Of course, Mumbai (formerly Bombay and the biggest city in India) is another story. Good luck!

Albuquerque — half a world away — gets to see the shower in the middle of the afternoon (3:30 pm), the day before.

Further Surfing:

Leonids, NASA

U.S. Naval Observatory: World Time Zone Map

U.S. Naval Observatory: U.S. Time zones

U.S. Naval Observatory: Universal Time

(Answered Nov. 15, 2002; updated Sep. 27, 2007)