With air pollution warnings issued today and Thursday in the region, people with asthma, emphysema and other respiratory illnesses are advised to take it easy.

High ozone levels are blamed for the advisories, but in hot, humid weather, soot and other pollutants mean people with lung ailments won’t be breathing easy this summer.

Symptoms include coughing, phlegm and shortness of breath.

“There’s a lot of symptoms, and those symptoms all mean trouble,” said Dr. James Murphy, a Dayton pulmonologist and critical care medicine specialist. He works in private practice and is the medical director of the intensive care unit at Miami Valley Hospital.

“The number one strategy is definitely to avoid all those things that are irritating the lung.”

A smog alert is in effect today in Butler and Warren counties, said Megan Hummel, spokeswoman for the Southwest Ohio Air Quality Agency. High ozone levels are expected, which will make it difficult for people with respiratory illnesses to breathe.

Temperatures are expected to reach 100 Thursday.

The Regional Air Pollution Control Agency has also issued air pollution advisories for today and Thursday in Clark, Greene, Miami and Montgomery counties.

Air quality experts monitor weather patterns and particulate levels daily, Hummel said. “If you do have respiratory issues, you definitely want to pay attention to the Air Quality Index,” she said.

On days like today, it’s a good idea to work out indoors, she said, and to limit strenuous outdoor activity.

The Miami Valley’s rivers, topography, climate, emissions from interstate traffic and industry and the abundance of pollen and mold all combine to make it a perfect spot for not-so-perfect air quality.

Nationally, the Dayton-Springfield-Greenville region ranks 17th out of 277 metropolitan areas for annual particle pollution, 38th for high ozone days and 80th for 24-hour particle pollution, according to the American Lung Association’s “State of the Air 2012” report.

But the air is cleaner than it used to be, and efforts are in the works to make it cleaner still, said John Paul, administrator of the Regional Air Pollution Control Authority.

“You can ask the question is any level of air pollution not harmful to your health? And there probably is no level that’s not somewhat harmful to your health,” Paul said.

Ozone, produced when sunlight and emissions from vehicles, power plants or industrial plants mix, irritates the airways and reduces lung function. It exacerbates the effects of asthma, emphysema and other lung diseases.

Particulates, or soot, aggravate lung disease and can also contribute to heart disease if very small particles get lodged in the lungs. Very small particles have been linked to heart attack, stroke and premature death.

During the summer months, humid, still air means poor air quality. “Humidity is a big deal, regardless of how clean the air is,” Paul said.

Humidity can actually help lower ozone levels in cooler weather, but heat, coupled with sunlight, brings those levels back up. And high humidity means soot and other pollutants tend to hang around.

Health experts have decades of data showing that air pollution is unhealthy.

“For 40 years, we’ve looked at increased hospital admissions, increased asthma attacks, people having problems if they’re exercising,” Paul said. “A lot of the advisories we issue are aimed toward that.”

For the last few decades, experts have also seen an increase in adults developing asthma, Murphy said. Long-term exposure to low-levels of pollution, including secondhand tobacco smoke, may play a role, he said, but it’s difficult to tease out individual culprits.

For consumers, the bottom line is to be sensible on days when air quality advisories are issued. That means staying inside when pollution levels are at their highest, limiting physical activity outdoors and taking steps to cut down on pollution, such as using public transportation or filling up the gas tank after 6 p.m., Paul said.

Running the air conditioner can also reduce exposure, Murphy said.

Tighter soot standards proposed this month by the U.S. EPA will reduce heart attacks, asthma and save lives, health experts say. The agency wants to cut the acceptable annual levels for fine particle pollution from 15 micrograms per cubic meter to 12 to 13 micrograms.

EPA officials say 99 percent of U.S. counties are already projected to meet the new standards without added actions.

An analysis by the American Lung Association finds that, nationally, the proposed standards would prevent 35,700 premature deaths; 2,350 heart attacks; 23,290 emergency room visits; 1.4 million asthma attacks and 2.7 million missed work or school days.

If approved, the new standards will go into effect in December. Counties have to have plans in place to meet the standards by 2015, and be in compliance by 2020, Paul said.

RAPCA is already measuring particle pollution based on the new standards, he said.

Vehicle emissions play a large role in air pollution, and some studies have shown that people who live in high-traffic areas have more health problems linked to poor air quality.

Next year, the EPA will require near-roadway air quality monitors to be installed in metropolitan areas with 1 million or more people to measure pollution levels. Paul said he expects to see the near-roadway monitors installed in 2014 or 2015 in the region.

New national measures tightening emissions on coal-fired electric generators aim to reduce particle pollution; and in Ohio, 11 of those plants are to be shuttered by 2015. U.S. measures to reduce sulfur in gasoline for light-duty vehicles will also cut particle pollution.