Is air pollution a problem associated with fossil fuel?

For many people, yes.

Pollution is, like "weed", a matter of opinion. I like dandelion and violets growing in my yard, while others call them weeds. You can define a perfect lawn as being 100% Kentucky bluegrass, which would make zoysia grass or fescue grass weeds. Others deliberately cultivate a zoysia, fescue, or even a bentgrass lawn.

There is no agreement on what the chemical composition of clean air is. It's about 4/5 oxygen and 20% nitrogen, but such air is lacking the gaseous water that form clouds. Your body requires carbon dioxide, or else it doesn't inhale and exhale. When you exhale, you add water vapor and carbon dioxide to the air, which are the chemicals primarily associated with burning fossil fuels.

As I write this, my body is being warmed by a stove burning kernels of corn. It's no different than burning oil or coal, except that the corn was grown this year, a process that removes carbon dioxide and water from the atmosphere. So my corn fire is carbon neutral. It adds nothing to global warming, unlike fossil fuels (coal, oil and natural gas). You might like to think of coal and oil as corn that's been sequestered for a long, long, time.

When I passed through Gary Indiana a couple of decades ago, the air was not at pleasant. I commented on it to the guy pumping my gas, and he said, "Yeah, ain't it wonderful? That's what prosperity smells like!"

And there are many people who find pipe tobacco to be a pleasant fragrance, but to me, it can cause a life-threatening Asthma attack. Air pollution is associated with the consumption of any fuel, whether it's a fossil fuel or not, and if you're a radical environmentalist, you'd be in favor of all life forms not using photosynthesis for an energy force.