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By Tim Brown, Operations Manager, County Information Project |
The U. S. Environmental Protection Agency makes data available to the public on the amount of hazardous air pollutant (HAP) emissions from major, area and other, on-road mobile, and non-road mobile sources by county.1 The accompanying maps show the weight, in pounds, of total and onroad HAP emissions from 1999. On-road mobile sources consist of licensed motor vehicles, including automobiles, trucks, buses, and motorcycles. Non-road mobile sources consist of 2- or 4-stroke gas and diesel engines, non-road vehicles, aircraft, commercial marine vessels, and locomotives.
As one would expect, the large urban areas of the state, particularly the Houston-San Antonio-DFW triangle, contributed by far the most HAP emissions (see Map I). There were 71 counties that released more than 2 million total pounds each of HAP in 1999; twelve of which released more than 10 million pounds of HAP each. In fact, five counties (Bexar, Dallas, Fort Bend, Harris, and Tarrant) contributed 30.4% of the total HAP released in Texas that year.
Given that these are all large urban counties and recent news articles about urban congestion, the natural assumption would be that the majority of emissions in these counties came from on-road sources. In three of the five previously mentioned counties, on-road emissions accounted for more than 50% of the total HAP released. However, this was not the case in Fort Bend (16.7%) or Harris (39.1%). Similarly, on-road emissions accounted for only about a third of all HAP emitted statewide in 1999 (227.2 out of 681.6 million pounds); and only 21 counties had more than 2 million pounds of on-road HAP emissions.
