Despites some improvements over the past decade, the air most Marylanders breathe still can make them sick and even cause premature death.

That's the upshot of a new report by the American Lung Association, which after analyzing air quality readings from 2005 through 2007 finds that Baltimore city ranks 15th among U.S. counties with the worst short-term particle pollution.  

The greater Washington-Baltimore region was judged to have the 14th worst ozone pollution, with 28.8 days a year, on average, when smog reached unhealthful levels.  That's better than it used to be.  A decade ago, the region averaged 42 days a year of bad ozone.  But the short-term trend is headed in the wrong direction - the region only had 26.3 days of unhealthful ozone levels from 2004 through 2006, according to the group. 

Though fine-particle pollution is worse in the city, it's a problem elsewhere in the state as well.  Baltimore County joined the city in earning a "failing" grade from the lung association for short-term particle levels, while Anne Arundel and Prince George's counties got "D"s for having at least a handfull of days with harmful particle pollution every year.

Baltimore once ranked second only to Los Angeles for having the worst summertime ozone, or smog.  Ozone levels have improved, with fewer days of really high readings.  But that good news has been offset by research finding that air pollution is still harmful at lower levels.  In response, the Environmental Protection Agency last year tightened its standards on ozone pollution.

Of 15 counties in Maryland where air quality is monitored, all but two scored failing grades for ozone pollution from the lung association.  The only two that didn't flunk - Baltimore city and Worcester County - didn't have enough air data to analyze, the group said.

Ozone is produced when chemicals from vehicle exhaust and power plants mix in hot sunlight. It can cause a sunburn-like inflammation of lungs and bronchial passages, leading to shortness of breath, chest pain, wheezing and coughing.  It can worsen asthma and even cause premature death.

Particle pollution is also a silent killer.  It's a toxic mix of microscopic soot containing chemicals and metals from diesel exhaust and other forms of combustion.  Even short-term exposure to elevated levels can cause health problems, including heart attacks, strokes, asthma attacks and premature death.

Maryland's air picture is mirrored nationally.  Despite progress in many cities over the past decade in curbing ozone pollution, the lung association found that 60 percent of Americans still breathe harmful levels of either ozone or particle pollution.  The group wants EPA to tighten air pollution cleanup requirements even more - meanwhile, it urges people to drive less and use less electricity, avoid burning wood or trash and urge local school systems to replace old diesel buses with cleaner vehicles.

To read the ALA's latest "State of the Air" report, go here.  You can also find out how the air is in your area by typing in your Zip code.