The region's second consecutive mild summer produced just one Code Red exceedance of the Environmental Protection Agency's one-hour standard for ground-level ozone in 2004, compared with two exceedances in 2003. That's good news indeed. However, ground-level ozone loves the kind of hot, humid, stagnant conditions we experienced in 2002, when there were 16 Code Red exceedance days. That's not so good. That means that there were 16 days when it was unhealthful for young children, the elderly, anyone with chronic health problems and even some healthy adults to be out-of-doors.

However, a look at the last 20 years of data, going back to the summer of 1985, helps put things in perspective. In 2002, our summer weather was similar to that in the summer of 1988. In 1988 there were 36 exceedance days, more than twice as many as in 2002. Regulations on industry, cleaner fuels and cleaner vehicles have all made a huge difference in our air quality, by reducing the emissions of pollutants that make up ozone. Voluntary actions by individuals and businesses, which have been promoted by Clean Air Partners and its predecessor organization since 1995, are also making a difference.

Despite all that progress, the Baltimore region still has not attained the EPA's health-based standard for ozone. Based on research that indicates that prolonged exposure to even lower levels of ozone can be harmful, the EPA is adopting a new standard based on the average concentration of ozone over eight hours. The eight-hour standard may result in more Code Red days.

The EPA also announced in December that the Baltimore region does not meet federal standards for particulate matter, or particle pollution, which is the mixture of solid particles and liquid droplets in the air we breathe. Unlike ozone, particles are not a seasonal pollutant. High readings can occur at any time of the year. Particles can come from sources such as motor vehicles, construction sites and wood-burning fireplaces and stoves, or can be formed when gases from burning fuels react with sunlight and water vapor. Very small particles less than 10 microns in diameter pose the greatest health problem, because they can get deep into the lungs, and may even get into your bloodstream.

The Maryland Department of the Environment is working with the 13 states in the Ozone Transport Commission to push for aggressive new controls at upwind power plants to reduce fine particle pollution. As with ozone, fine particles and their precursors can be transported over hundreds of miles. Other actions like acid rain controls, Maryland's Vehicle Emissions Inspection Program and reformulated gasoline requirements have all helped lower particle levels in the last decade. Particle levels in Maryland have dropped about 25 percent since the early 1990s as a result of these efforts.

Is our air getting cleaner? Yes. Is it clean enough? Not yet. And that's why it's still important for each of us to keep doing our share for cleaner air.