Where ever you live, you're probably being exposed to all sort of pollution. The obvious kind is chemical and comes in the form of smog and waste. The more subtle form is emotional pollution. Emotional pollution happens when you come into contact with people who are irresponsible with (or just unaware of) the way they affect the environment with their decisions, their anger, their jealousy, and their pessimism. When you're around them, they suck you into their negative thinking and judgmentalism and sap the levity, humor, and joy from a situation.
The good news is that while chemical pollution is difficult to convert into a less noxious form, emotional pollution is a bit easier if you have the right tools. You first have to vigilant and aware when you're entering a polluted area. The sooner you identify it, the better. Next, you have to avoid contributing to the person's negativity. Don't join them, but also don't fight them, since fighting them is just another form of negativity. You keep your composure, keep your levity, and keep your optimism close to you and quietly model a different way of thinking and living.