Even burning only leaves put carcinogens in the air. Depending on the plants burned, these smoldering fires can even spread toxins that can cause allergic (and even seriously harmful) reactions. Living plants also pull pollutants out of the air. When these plants are then burned, those pollutants are released into the air once again.
Unfortunately, our house is in the low spot of our neighborhood. The smoke from our neighbors often flows towards and then settles in our yard. On a day like today, where the weather was nice and we could finally open our windows to let in the fresh air, having the house fill with acrid smoke is even more infuriating.
I'm tempted to go out and hose down the ashes they have left smoking.