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A Case Study: Texas Air Quality


Houston meets five of the six National Ambient Air Quality Standards set by the EPA. It exceeds the standards for ground-level ozone.

houston air quality 2007
From the Houston Regional Monitoring Network

The high ozone concentrations are the result of several factors:

  1. Proximity to the largest petrochemical complex in the world. Taken together the many industrial plants release significant quantities of volatile organic (carbon-based) compounds,
  2. Large numbers of cars being driven many miles per day. 4.7 million people live in the sprawling metropolitan area.
  3. Many hours of sunlight,
  4. A strong sea breeze that produces atmospheric conditions that enhance smog to smog formation. The sea breeze blows strongly offshore peaking in the early morning hours. Then the air reverses, peaking in late afternoon. Pollutants put into the air turn to smog during the day. Weak winds from morning to early afternoon keep the pollutants over the city. During the night they are blown offshore, only to return later the next day.

To understand the Houston air quality,

The air quality in Houston is monitored more closely and analyzed with more intensity than perhaps anywhere in the country--possibly the world. That's because the factors contributing to the region's ozone and air toxin problems are numerous and complicated.
Texas Commission on Environmental Quality

Past History

We know much about air quality in Texas thanks to a large air monitoring network.

According to the EPA's Office of the Inspector General, the state of Texas has the largest ambient air toxins monitoring network in the country, larger than California's, New Jersey's, Louisiana's, Oklahoma's, Mississippi's, and Florida's combined.
Michael Honeycutt, manager, toxicology section, Texas Commission on Environmental Quality, 2005.

The Texas Commission on Environmental Quality publishes information about all large scale pollution events in the state on their Air Pollution Events page. An example is the 1 September 2006 event. The web page contains links to many important sources of data that help explain the event, including animations of the event.

Other useful information include:

  1. Air trajectory maps for cities throughout the state at their Air Trajectories page, showing where the air came from and the path it took over 48 hours to arrive at the city and the forward trajectories showing the path the air is projected to take over the next 36 hours from city.
  2. Ozone data for many areas at the Ozone Data page, including historical data about past extreme events.


Work by state and local officials and local industry is reducing the number of days exceeding the federal limits for ozone concentration. The number of days has fallen from a peak of 80 days in 1982 to 35 days in 2003 according to the Houston Regional Monitoring Network.

The strategy for future reductions is described in the State Implementation Plan (SIP). The plan focuses on:

  1. Reducing highly reactive volatile organic (carbon-based) compounds (HRVOCs). The four compounds of interest are 1,3-butadiene, ethylene, propylene, and the butanes. The goal is to find and reduce the emissions of small amounts of compounds from hundreds of sources. They hope to obtain reductions in both short-term and annual HRVOC emissions from four key industrial sources: fugitive emissions, flares, process vents, and cooling towers.
  2. The reduction of NOx. Including improved control of emissions fro large, stationary diesel engines.
  3. Improved monitoring to tie emissions from specific sources to ozone levels.

More work is needed. Eight scientists from the Houston, in a report published by the Department of Civil and Environmental Engineering of Rice University, area recommend that four carbon-based compounds additional be regulated: benzene, 1,3-butadiene, formaldehyde, and diesel particulate matter.

According to Environmental Defense analysis of 2002 Toxics Release Inventory data, Harris County ranks third in the country for toxic air emissions with 20,449,130 pounds. Of course there are certain areas of the county that are hot spots for toxic air emissions due to their proximity to sources. Nearly ten percent of the county's emissions are released from four industrial plants in the Milby Park area, south of the Houston Ship Channel.
Jane Laping, executive director, Mothers for Clean Air, 2005.

EPA risk assessments for cancer make Harris County number 1 in added cancer risk in Texas, although several other counties are close behind. Data from the National Cancer Institute indicate that historical cancer death rates in Harris county are higher than the national average although not as high as some nearby counties. We really cannot say whether the elevated air pollution levels are directly linked to health effects. To answer that question we would need to conduct large studies that would require air monitoring data that we do not have.
Jonathan Ward, director of the division of environmental toxicology at University of Texas Medial Branch - Galveston.

The Harvard Center for Cancer Prevention estimates 2% of cancer deaths are attributable to environmental pollution (including water, soil, and air). Under these conditions, it is difficult to measure cancer risk due to ambient levels of air toxics. ... Research has shown that ambient (outdoor) air toxics concentrations frequently play a minor role in actual personal exposure to air toxics. This is due to indoor (e.g., formaldehyde) and mobil source pollutants and their often greater impact on personal exposure.
Michael Honeycutt, manager, toxicology section, Texas Commission on Environmental Quality, 2005.

Quotes from a Roundtable Discussion on Air Quality in Houston 19 December 2005 reported by the Houston Chronicle.

Other Useful Information

NASA has a web page on Getting the Big Picture on Houston's Air Pollution

AIRNow publishes present information on air quality and forecasts for major cities in Texas and throughout the country, and measurements of particulates and ozone. See maps:

  1. National Map with links to forecasts at major cities.
  2. For Ozone.
  3. For Particulates (PM2.5).
  4. Texas Air Quality Conditions and Forecasts

The maps report the Air Quality Index, a standardized scale devised by the EPA for reporting air quality. Charts are provided for four pollutants: ozone, particle pollution, carbon monoxide, and sulfur dioxide. The AQI for nitrogen dioxide is not included ... because nitrogen dioxide levels across the country have been below the national air quality standard for the past several years. Nitrogen dioxide levels are usually so low that they pose little direct threat to human health. Nitrogen dioxide, however, is a concern because it plays a significant role in the formation of ozone, particle pollution, haze, and acid rain. From AIRNow.

Want to see what the air looks like now? WebCams at:

  1. El Paso,
  2. Big Bend,
  3. Cucamonga California,
  4. Berks County Pennsylvania.

Be sure to click on the landmarks link on the webcam pages to find location of landmarks that should be visible but may not be.

Revised on: 5 January, 2009

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