Exercising outdoors can be quite therapeutic for several reasons. I love jogging early in the morning for the joy and peace of a tranquil workout. Being alone for a brief session at the prime of my day is exciting and rewarding; what a great way to start my day! 

But, with all the wonders of working out outside be forewarned that there are several dangers, too.

Dr. Crystal says that epidemiologic studies have linked air pollutants to harmful effects on the heart and lungs, to emergency hospital admissions, and to deaths. The pollutants affect the lungs by causing inflammation or irritation of the airway lining. More mucus and phlegm is produced, he says, and small muscles surrounding the airway respond by squeezing down. The work of breathing increases and it becomes more difficult to get oxygen into the body.

In addition to fine particulates -- which are emitted by the diesel engines of trucks and buses -- the two most significant environmental culprits are carbon monoxide and ozone, Dr. Crystal says. Carbon monoxide arises from cigarette smoke and automobile exhaust. It has a tremendous ability to force oxygen out of our circulatory system -- it combines with hemoglobin 200 times faster than oxygen. Overexposure may lead to headache, dizziness, confusion, and dangerous increases in body temperature.

Ozone, which is a large component of the smog found in cities like Los Angeles and New York, results from the interaction of sunlight and chemicals found in car exhaust. Ozone adversely affects a person's breathing pattern and causes the airways in the lungs to become smaller and more resistant to oxygen exchange. Because of ozone, a person working out has difficulty taking deep breaths, and has to breathe faster. As a result, the exercise becomes more stressful and difficult.

Dr. Crystal offers these simple tips:

• Do not run on or near roads where there is heavy truck or bus traffic.
• Work out in the early morning or later in the evening.
• Exercise indoors if possible.
• If you experience any difficulty breathing, stop your exercise immediately and see your doctor.

Of course Detroit is in the Top 10 Most Polluted US Cities; that stinks.

Stay safe, run in clean air where there's plenty of trees, plants, and vegetation, and less motor vehicles.