Should I worry about pollution when I am walking outdoors?

Worry? No.  Take precautions? Sure.

There's not much you can do if you live and work in the city.  Smog and exhaust from vehicles is everywhere.  Look at this way - walking outside in the city is still better than sitting watching TV.  If you jog in the city, you might consider wearing a scarf or bandana over your nose and mouth area.  And try to find paths away from traffic if you can. 

Walking outdoors shouldn't be an unhealth experience. Unfortunately, we all can not live out in the country. In a perfect world, I personally would want to walk in an area with the least amount of air pollutants as possible. The breathing in of air pollutants while you are walking will cause this air to go into your lungs and this air will be used to oxygenate your blood. This can adversely affect your body over a long period of time. Walking in these situations occasionally should not affect you. But over a long period of time this could cause lung and other problems. Personally, I would want to provide my body with the best air quality as I possibly could give it. But that is not always possible. So, should you worry about pollution when you are walking outdoors? I would say that you should worry about anything that affects your body negatively. And try to supply your body with the best fuel (oxygen) it needs to keep you working at its best. 

If you have respiratory problems, then pollution is a concern.  Most locations local news have alerts notifying you of the air quality.  Pay attention to those, and if the air is not conducive to your respiratory level, walk a treadmill indoors.  Do not let the pollution level stop your cardio.

Air pollution can affect your performance when walking outdoors, especially if you have asthma or any other respiratory disease. You can visit www.scorecard.org to determine if a certain area has air pollution. During pollution warnings it may be best to exercise indoors.