The quality of the air in Houston has been an important issue ever since the passage of the Texas Clean Air Act in 1967 and the federal Clean Air Act of 1970. Following those Acts and their Amendments, there have been studies of pollutants, debates over control strategies, revisions of acts and new dates for attainment set - all with the goal of much cleaner air for everyone to breathe. The current date for achieving this is now 2007.

As is evident from the Air Quality Reference Guide for the Houston-Galveston Area (1.4mb PD file) achieving and maintaining good air quality is a complex task. The six important air pollutants were identified early and the amounts permissible in the air (the standards) were set soon thereafter (see Table 1 of the guide). Many of the major cities in the country fail to meet one or more of these standards for pollutants (see Table 2 of the guide), and Houston-Galveston area is fortunate that it meets the standards in five of these pollutants and falls for only one pollutant -ozone.

There are five air pollutants (for which the area meets the standards): carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, and lead resulting from industrial activity, transportation and sometimes from natural causes. Carbon Monoxide, a colorless, odorless gas, is formed in the burning of wood, gasoline, and other fuels. Sulfur Dioxide, also colorless and odorless (at low concentrations), is emitted from power plants burning high sulfur coal, refineries and sulfuric acid plants. Nitrogen Dioxide, a yellow-brown gas, is formed during high temperature burning of fuels in industrial processes, motor vehicles, furnaces and kitchen stoves. Its control is important for it is involved in the formation of ground level ozone. Particulate matter describes the small particles in the air - everything from simple dusts and soot to microscopic salts of organic and inorganic compounds. Lead is a well-known poisonous metal previously used in gasoline and paints. It is emitted from smelters, battery manufacturing plants, and the burning of lead-containing coal. Its use has declined significantly and measurements of lead in Houston's air are now nearly undetectable.

Ozone (for which the area does not meet the standard) is the only one of the six major pollutants which is not emitted directly into the air. It is a highly reactive form of oxygen, and is found naturally, in the stratosphere where it protects people from ultraviolet rays. It is formed at ground level, through a complex series of reactions in the presence of sunlight, involving the emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) from industrial processes, motor vehicles of all types, and many other sources. These include off-road vehicles such as trains and construction equipment, area sources such as gasoline stations and dry cleaners, and natural "biogenic" sources such as various trees and plants. NOx results from high temperature combustion. Many factors influence the formation of ozone: the amounts of VOCs and NOx (called precursors) being emitted, the reactivity of the VOCs, the amount of sunlight, the windspeed, and other meteorological conditions, and the amount of time needed to form ozone.

The quality of the air in the Houston-Galveston area is measured by a combined system of over twenty-three air quality monitoring stations. The basic system was established by the City of Houston in 1971. The Texas Natural Resource Conservation Commission (TNRCC), in its predecessor agency, the Texas Air Control Board, added more monitors in 1973. An industry group, Houston Regional Monitoring, began ozone monitoring in 1981. Most of these monitors measure other criteria pollutants as well as ozone (which is continuously monitored), and other meteorologic data. Most of the monitoring stations are located in Harris County. However, four of the eight counties in the Houston-Galveston area have no monitors at all ( See Figure 2 of the guide).

The concentrations of ozone, recorded at the monitoring stations operated by the City of Houston and by TNRCC, determine whether or not the area is meeting the air quality standard. To meet the standard, the one-hour average concentration of ozone cannot be exceeded at any one monitor in the area on more than three in a three year period of time. Therefore, the area cannot have more than three measurements above the standard (0. 12 ppm.) at its worst monitoring station during a three year period and meet the qualifications for clean air. The greater the number of days in which ozone is above the standard, the greater the severity of the problem. The EPA has designated areas of the country from Extreme (Los Angeles) to Severe (Houston) to Moderate (Beaumont-Port Arthur) (see Table 5 of the guide). These designations determine the amount of pollution controls needed and the dates when the standard must be reached.

Although the number of days in which the area has exceeded the ozone standard have generally decreased since the late 1970's, there has been notable increase in exceedence days in the last few years. Most have been in the recognized smog season, April through October.

The earliest efforts to control the formation of ozone, was through the control of emissions of VOCs emitted from industry and motor vehicles. Recently, there is an increased effort to control NOx, to see if ozone concentrations can be reduced even more with a combination of control strategies. These are currently being discussed by EPA, TNRCC, and several levels of government and agencies. Eventually the strategies will be proposed as the revised State Implementation Plan (SIP).

There are five major groups of sources of VOCs and NOx, which will have to meet the new control strategies proposed in the revised SIP, as well as the controls and permits required from earlier clean air acts and amendments.

• Point sources - large industrial or commercial plants, such as refineries - which can emit both VOCs and NOx.
• Area sources - smaller businesses, such as service stations and dry cleaners – which emit more VOC than NOx
• On-road mobile sources - cars and trucks of all types - which emit both VOCs and NOx
• Off-road and non-road mobile sources - airplanes, boats, trains, and construction equipment - which emit VOCs and NOx.
• Biogenic sources - all sorts of crops and trees - which can emit VOCs but which are also very beneficial in removing other pollutants from the air.

The plan for cleaning up the air in Houston is derived from a computer model that is run by the TNRCC. The State inputs various control measures and the computer computes the effect on ozone levels. In May of 1998, the TNRCC demonstrated that a reduction of 100 percent of the VOC's would not be sufficient to bring the Houston area into compliance. The model indicated that nitrogen oxides would have to be reduced by 65-85 percent from all sources. Additional VOC reductions of 15 percent will also be required to prevent a transitory increase in ozone levels.

The following are some of the VOC and NOx control measures that are being considered from the various sources :

Stationary Sources

• Installation of Reasonably Available Control Technology (RACT) such as low NOx burners or modification of combustion operating procedures. Additional controls such as Selective Catalytic Reduction.
• Voluntary emission reduction from grandfathered sources or potentially mandatory reductions if needed.

On-road Mobile

• Expansion of Inspection & Maintenance to 8-county region
• Cleaner gasoline and diesel fuel and alternative fuels
• National low emission vehicle standards, including even stricter standards for light-duty vehicles, and for the first time, gasoline and diesel sport utility vehicles and light-duty trucks.
• Low emission standards for fleet vehicles
• Transportation control measures
• Accelerated replacement of older vehicles

Non-road Mobile Sources

• Low-emission heavy duty diesel and locomotive standards
• Compression and spark ignition standards for vehicles and equipment
• Low-emissions standards for recreational vehicles, commercial marine vessels, and recreational marine vessels
• Cleaner gasoline and diesel fuel
• Shift construction activity to afternoon
• Additional measures to reduce NOx

Area Sources

• Low Nox standards for new water heaters and furnaces
• Vapor recovery at gas stations in eastern Texas

TNRCC will be submitting control measures to EPA in November 1999. The State will also be required to submit fully adopted rules to achieve the emission reductions they have proposed by the end of the year 2000.

Progress has been made in emission reduction over the years. It is estimated VOC's will be reduced by 77 percent between 1970 and 2000. These reductions have come from all categories: industry, cars, small businesses and consumer products. Federal, state and local regulations have contributed to reductions. To achieve compliance everyone must help reduce ozone precursors. There is a list of activities included in this handout that an individual can initiate to reduce pollution. Sonoma Technologies, Inc. performed a study on Houston to determine the cost of unhealthy air. That study concluded that the total annual economic benefits of reduced exposure addociated with achieving compliance with the one-hour ozone and fine particulate standard in 2007 are in the range of $2.9 billion to $3. 1 billion in the Houston area. Failure to meet the standard by the year 2007 can also result in lost transportation funding and higher emission reduction ratio for new industries.

For a more in-depth look at air quality, the Air Quality Reference Guide for the Houston-Galveston Area can be obtained from the Houston-Galveston Area Council.

BIBLIOGRAPHY

Air Quality Reference Guide for the Houston-Galveston Area, 4th edition, Regional Air Quality Planning Committee, Houston-Galveston Area Council, Houston, TX (This is a 1.4mb pdf file)

Updated: Mon, Aug 28, 2006