Simply put, an aerosol is a collection of solid or liquid particles suspended in a gas. This is a pretty general definition and include lots of types of particles – hairspray, oil from frying meat, spray paint, etc. For particle camp, the aerosols that we are concerned with are the ones that make up air pollution.
Smog. What you see when you look at smog is mostly aerosols. The particles scatter light, reducing visibility. The stereotypical brown color of smog is from gaseous nitrogen species (NOx to be specific).
Some familiar aerosols include:
Even huge duststorms, like ones you can see from space that carry plumes of smoke from the Sahara that can be detected in the southern US.
The original, the classic – Los Angeles
San Francisco is not immune.
Here is a good example of how a good rainstorm can clear the particles out the air, resulting in a temporarily clean atmosphere until it builds up again. This is Beijing. China has horrid air quality, often much worse than we have ever seen in the United States.