Because of Pennsylvania's geographic location and industries, pollution has become the No. 3 killer in the state, according to a recent PennEnvironment study.

Nathan Willcox, energy and clean air advocate for PennEnvironment, said the report shows that air pollution has significant public health effects that include asthma, missed work and premature death.

"Studies show that where there is more air pollution, there is more death," said Dr. Rebecca Bascom, professor of medicine at Hershey Medical Center.

Willcox said there are two main sources of air pollution in Pennsylvania that contribute to health effects: coal-fired power plants and vehicle emissions.

Those two sources of pollution are especially high in Pennsylvania, Willcox said.

"The state has some of the dirtiest coal-fired power plants in the country," he said.

He added that because Pennsylvania has many major highways that connect to other states, traffic pollution is a significant problem as well.

"It is different here in Pennsylvania because we are the Keystone State," Willcox said. "There is so much traffic that goes through Pennsylvania, especially Harrisburg."

He said in Harrisburg, there is so much traffic that there are large warehouses built specifically for tractors-trailers to park overnight.

Willcox said smog pollution comes from cars and trucks and causes the inside of lungs to burn, similar to skin sunburn; it also contributes to asthma and respiratory infections.

Soot pollution comes from coal-fired power plants and diesel fuels. Willcox said soot pollution leads to premature death and chronic bronchitis.

Bascom said air pollution causes inflammation in the respiratory system that leads to cardiovascular and neurological damage.

Smoking was the No. 1 cause of death, with poor diet and poor physical activity at No. 2, according to the study, Willcox said.

Maurine Claver, director of environmental health and safety at Penn State, said the university was recognized by the Federal Environmental Protection Agency for its efforts to reduce mercury emissions in December 2005.

Claver said mercury is a cause of pollution in many mediums, including the air.

She said the university's efforts included working to eliminate mercury thermometers, mandating training for people working in labs with mercury and introducing a program to make sure chemicals are handled properly when transferred.

Bascom said mercury is one of the most individually toxic pollutants.

"A little bit of it causes a lot more harm than a little bit of many other things," Bascom said.