Houston’s Ozone Trends: Another Look

In December, we looked at how Houston fared during the 2013 ozone season, and whether it is continuing to make progress in reducing 8-hour ozone levels. This week, we will look at another ozone trend—the number of days that Houston exceeded EPA’s previous 1-hour ozone standard. We’ll also compare Houston’s tally to that of Los Angeles.

In 1999 and 2000, ozone levels in both Los Angeles and Houston were newsmakers. Los Angelenos were greeted by the news that for the first time since ozone measurements had been made, they were not the “smog capital” of the nation. Houston residents, on the other hand, were disappointed to find that they now held this dubious distinction.

In 1999 and 2000, ozone levels in both Los Angeles and Houston were newsmakers.  Los Angelenos were greeted by the news that for the first time since ozone measurements had been made, they were not the “smog capital” of the nation.  Houston residents, on the other hand, were disappointed to find that they now held this dubious distinction.  How had this happened?  In the 1990’s, Los Angeles had implemented new regulations on a variety of sources–everything from hairspray to auto body shops to industrial manufacturing.  In addition, California is the only state that Congress gave authority to in the Clean Air Act to regulate engines and fuels, which they had done.  These measures combined to help Los Angeles clean up its ozone at a faster rate than any other area in the nation.  Los Angeles also experienced milder weather in 1999 in particular, while those of us in Houston in 2000 remember it as one of the hottest, driest years on record. Texas had not sat idly by, and had enacted a suite of regulations of its own.  Houston industries made reductions in both oxides of nitrogen and volatile organic compounds (NOx and VOCs–ozone’s chemical building blocks), and a vehicle inspection and maintenance program was put in place to require car owners to fix high-polluting vehicles.  Refueling your car also got a lot cleaner in Houston as gas stations were required to install vapor recovery systems.   Unlike California, Texas had to rely on the federal government to pass new nation-wide regulations on gasoline and diesel engines and fuels.  These federal measures did not start to be phased in until 2004. What happened next?  The graph below tells the story.

LAHouston
Data Sources: http://www.tceq.state.tx.us/cgibin/compliance/monops/ozone_exceedance.pl and http://www.aqmd.gov/smog/o3trend.html

This graph shows the number of days that a monitor anywhere in either the Houston or Los Angeles regions recorded an exceedance of EPA’s older, one-hour ozone standard.  In the early 2000’s, Houston’s ozone levels began to show signs of a decline.  By 2004, when a number of stringent new state regulations on business and industry took effect, the decline was notable.  One-hour ozone levels have continued to stay low, and the Houston region has attained the older, one-hour standard for several of the past few years, including the most recent three year period—2011, 2012, and 2013.

One-hour ozone levels have continued to stay low, and the Houston region has attained the older, one-hour standard for several of the past few years, including the most recent three year period—2011, 2012, and 2013.

The graph also tells us that Los Angeles regained the “smog capital” title by 2001, but has also maintained steady progress in reducing ozone.  Did you notice that LA spike in 2003?  We know that weather conditions can change from year to year—a cooler, wetter, breezier summer will generally form less ozone.  But a drier, hotter year can mean higher ozone levels.  That’s one of the reasons Houston had higher ozone in 2000, and probably accounts for much of LA’s big spike in 2003.  In addition, wildfires can play a role in producing ozone-forming emissions in both Houston and LA.  Despite these year-to-year changes, it’s clear that there has been dramatic progress in both regions. Do Houston and Los Angeles meet EPA’s new, more stringent 8-hour ozone standard?  No, neither area does.  However, in 2013, Houston experienced both lower ozone levels, and fewer ozone days than ever before.  EPA is set to lower the ozone standard again in 2015, and it will take continued efforts from everyone—business, industry, government and citizens, to keep improving our ozone levels in the years to come. Want to Learn More? Newspaper clips from the Los Angeles Times in 1999 and 2000 give a good overview of the ozone status of the two regions at that time and what scientists and policymakers were saying about it. http://articles.latimes.com/1999/oct/13/news/mn-21768 and http://articles.latimes.com/2000/aug/24/local/me-9609 Here is more information about how EPA’s ozone standards have changed over time.  http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_history.html