WHERE DO AIR EMISSIONS COME FROM?
Air emissions come from four general types of sources. In the following discussion, we’ll talk about those sources, the types of emissions from those sources, and what can be done to control those emissions.
1. Point Sources are large, stationary equipment that emit constituents into the air through a stack or duct. Examples include: boiler and heater stacks, vents from factories, exhaust stacks from large turbines, and similar equipment.
Generally, these sources emit the products and by-products of burning fuel, though some sources vent constituents from processes other than combusting fuel. The regulated conventional pollutants from fuel combustion are: Carbon Monoxide (CO), Nitrogen Oxides (NOx), Sulfur Oxides (SOx), Particulate Matter (PM), and Volatile Organic Compounds (VOC’s). The largest-volume compound emitted by combustion sources is carbon dioxide (CO2), however CO2 is not regulated by rules or permitting; though it is the center of attention in the global warming/climate change debate. Total combined emissions of the conventional pollutants in Texas topped the 2 million ton mark in 2000. For the Jefferson, Orange, and Hardin County area, total point source emissions amount to approximately 311 tons per day.
Controlling emissions from combustion sources boils down to efficient combustion equipment, and clean fuel use. Stack treatment systems can also be used to “scrub” gases both before and after burning – though the technologies are different. For sources emitting VOC’s, refrigeration, adsorption on activated charcoal, or catalytic converters (similar to your car’s exhaust system) can be used to recover gases before they are emitted to the atmosphere.
2. Mobile Sources are essentially planes, trains, lawnmowers, outboard motors, cars, and trucks. While there are several categories of mobile sources, they all emit the products from burning gasoline, diesel fuel, or jet fuel.
For Jefferson, Orange, and Hardin Counties the mobile source pollutants of most concern are those that contribute to the formation of ozone e.g. VOC’s and nitrogen oxides. The mobile sources in our area emit 33 tons per day of VOC’s, and 96 tons per day of nitrogen oxides.
Emissions from mobile sources are controlled by more efficient combustion controls, maintaining proper air pressure in tires, properly tuned engines, use of cleaner fuels (e.g. low sulfur diesel, reformulated gasoline), and treatment of exhaust gases by catalytic methods.
3. Area Sources are smaller sources of air emissions that are reported as a group, rather than by individual facilities. These sources are grouped by similar emission constituents, and then all emissions for each pollutant are added up and reported county by county. Examples of Area Sources include: dry cleaners, residential natural gas usage, bakeries, auto body shops, service stations, furniture manufacturers, painting and coating facilities, landfills, and even smoke from structure fires.
Total emissions from Area Sources in the tri-county area are estimated to be 40 tons per day.
Emissions reductions from Area Sources are generally required on a category-wide basis, and the particular emissions control equipment is specific to the type of facility.
4. Biogenic Sources are emissions from nature. These emissions account for 30% of all Volatile Organic Compounds (VOC’s) emitted in the urban areas in the eastern half of Texas. When discussing Biogenic Emissions, VOC’s are usually the pollutants of concern. While most plants emit some VOC’s, pine, oak, sweet gum, eucalyptus, and poplar trees are the largest emitters. And some of the compounds these trees release are important in the chemical reactions that form ozone.
While it isn’t possible to control natural emissions, they must be quantified to obtain a better understanding of the complex atmospheric chemistry that produces ozone. This information is also used to develop strategies for those sources that can be controlled.
As mentioned earlier, VOC’s are the natural emissions that get the most discussion, but other pollutants are released by nature, sometimes in tremendous volumes and affecting enormous areas. Examples of other natural emissions include sulfur oxides, sulfuric acid, and hydrogen sulfide from volcanoes; and sulfur oxides and nitrogen oxides from forest fires.
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