Fifteen years ago, while driving west through southern
California, I watched the brilliant blue sky turn ominous, an
orangey-brown hue foreign to my eastern eyes. Was that a storm
approaching? Then it hit me; it was just Los Angeles.  David
Illif  Why did the sky look so gruesome? Car exhaust, I thought,
and the fact that L.A. sits in a sun-drenched valley. But I was
ignorant of the reason why smog is visible: particles. Smog is
full of tiny toxic blobs that turn the horizon ugly as they bake
in the sunlight. They can cause severe health problems from
asthma attacks to lung cancer. That’s why the EPA regulates
those kinds of particles. But the methods scientists use to
pinpoint the nastiest particles are far from perfect, according
to chemical engineer William Vizuete. “We’re not even sure what
happens in our bodies when we breathe in the particles that wind
up killing us,” he says. To find out, scientists need better
ways to study how particles interact with living cells. Vizuete
thinks his team has built a