Is it vehicles or industry? This is a common question about the largest source of air pollution in the Houston region. Unlike most cities in the country, the majority of air pollution in this region does not come from vehicles but comes from refineries and chemical plants. This makes Houston 's air pollution unique.
Ozone moves from its source
Ozone - our most well-known pollutant - is found at hazardous levels in every part of the Houston region. The source of the pollution that forms ozone is the region's industrial areas along the Houston Ship Channel or in other parts of eastern Harris County . While the highest levels of ozone and other air pollutants tend to be in places like Deer Park , near the Houston Ship Channel, weather patterns often steer the ozone toward the southwest area of Houston , and to the north, in the direction of Bush Intercontinental Airport .
Nitrogen oxides result from combustion
Ozone is a secondary pollutant, meaning that it does not come out of tail pipes and smoke stacks but is a result of a chemical reaction that requires sunlight. There are two classes of pollutants that are needed to produce ozone: nitrogen oxides and volatile organic compounds. Nitrogen oxides (NO x ) are formed in the air whenever there is any type of combustion or burning. About half the NO x emissions in theHouston region are from industrial sources including power plants. The remaining sources include vehicles, construction equipment, ships and trains, many of which are concentrated in industrial areas. (See figure 1.)
VOCs are not created equal
Volatile organic compounds (VOCs) are chemicals that evaporate readily, such as solvents. They come mainly from industry although smaller sources include gas stations and dry cleaners, vehicles, and even trees. But not all VOCs react the same. Formaldehyde and other industrial chemicals such as ethylene, propylene and butadiene are very reactive and form ozone far more rapidly than other VOCs. Most of the VOCs emitted from vehicles, construction equipment and vegetation do not produce ozone as rapidly as those from industry. (See figure 2.)
Particulate matter comes from diesel engines
In addition to ozone, fine particulate matter is another pollutant of concern in the Houston region. Fine particulate matter is made of tiny pieces of dirt and soot that are so small that they cannot be seen individually, but when grouped together make black smoke. Like the pollutants that make ozone, particulate matter also comes primarily from industry where it is most concentrated. Other sources of fine particulate matter in the Houston region are large trucks, construction equipment, marine vessels, and freight trains.
What needs to be done
One of the challenges in identifying sources of air pollution is obtaining accurate data. Although there are about 30 regional air monitoring stations that measure ozone, only a handful provide data on toxic ozone precursors such as benzene, butadiene and formaldehyde. Many air toxics are rarely or never measured by the state's monitoring network. Several efforts are needed for this region to achieve clean air:
- More monitoring to quantify emissions and determine their sources
- Stricter regulations to control VOCs and NO x from industry, the major source
- Increased controls on certain hazardous chemical pollutants to protect the public's health
- Improved technology to capture pollutants before they are released into the air
- Newly designed industrial processes to reduce or eliminate the use of hazardous pollutants
- Well-planned studies to determine the health effects of regional industrial pollutants to increase the urgency of cleaning up our air.
