Particulate pollution, as the name suggests, is made up of tiny particles, most of which you can't see unless they're clumped together. "You're worried about those that are 10 microns in size or smaller," says Tadlock. "A human hair is 70 microns, so these particles are significantly smaller." They're so small, in fact, that they get into our pores -- and that's where they do their damage. "It looks like those very fine particles cause skin aging," says Tadlock. "Nobody really knows how it works yet, but there's evidence. And whoever is living in the places with the highest levels of pollution is most susceptible."

Stateoftheair.org measures the particulate pollution over the last 24 hours. (This morning, my air was a C, which isn't great, but at least it passed.)

Because particulate pollution is almost like dirt gunking up your pores, you can get rid of it by washing your face … sort of. Your regular cleanser-plus-hands routine probably isn't going to cut it. Research shows that sonic cleansing is the best way to get rid of particulate pollution that's deep down in there. Tadlock recommends using a Clarisonic Cleansing Brush. "It oscillates and it's extremely gentle," she says. "And it cleanses 30 times better than manual cleansing."

If you're looking to amp up your exfoliation with sonic benefits, try the Skin Perfecter, $225. I'm currently obsessed. It's a metal spatula-like device that you glide along your skin in a choreographed pattern. It cleans makeup, dead skin cells and pollution(!) from your pores, while extracting clogs and increasing collagen production. Genius, right?

Unfortunately, when it's gray and smoggy, you may feel like you're getting less sun, but you're actually getting more. "Pollution enhances UV damage to the skin," says Beverly Hills dermatologist Debra Luftman, M.D. The particles of pollution magnify the ultraviolet radiation -- as pollution gets worse, so does our exposure to harmful UV rays. If you live in a polluted place, Luftman says you need to be even more religious about sunblock. She recommends using a sunscreen with titanium dioxide or zinc oxide because these minerals create a physical barrier against pollution. I like Coola Mineral Face Matte Tint SPF 30, $36, which has titanium, zinc and SPF-boosting botanicals -- and gives you a hint of color. Kate Somerville Daily Deflector Waterlight Broad Spectrum SPF 50, $48, is another favorite. It has anti-aging ingredients, a light texture and absorbs quickly.

Odds are you're not going to wash your face after every time you go outside. (Nor would your dermatologist want you to -- you'd dry out your skin and damage its protective barrier.) However, Luftman has a trick that's much more doable: Use a thermal water mist. "Spray that on top of your skin throughout the day," she says. "It can help negate some of the pollution." She suggests Avene Thermal Spring Water, $9. For even more anti-aging benefits, I like Tata Harper Hydrating Floral Essence, $65, which has jasmine and hyaluronic acid for added moisture. (There's currently a limited edition rose version available that's even more phenomenal.)