AN EVALUATION OF ACROLEIN STATIONARY SOURCE SAMPLING METHODS

The use of both natural gas and digester gas for producing energy has been on the rise in many regions of the country. Thus, there has been an increase in gas-fired power generating facilities that burn natural gas and/or digester gas through one process or another to generate heat and electricity. Despite the fact that natural gas is the cleanest burning of the major fossil fuels it does tend to produce some products of incomplete combustion, such as various carbonyl compounds. With this in mind, acrolein (2-propenal, acrylic aldehyde) is rapidly becoming one of the pollutants of increasing concern due to its potential adverse health effects and environmental occurrence. Of particular concern is the formation of acrolein by incomplete combustion of natural gas and digester gas in stationary combustion sources, such as boilers, turbines, and some classes of engines. However, the complexity of source testing for acrolein has led to some confusion as how to regulate acrolein and to interpret data gathered from the methods used to determine acrolein emissions.There are several methods of determining the levels of acrolein emissions from various sources. These methods include the Fourier Transform Infrared (FTIR) and, undoubtedly, the wet test methods. Wet test methods involve drawing a known volume of a gas stream through a sampling train containing chemical reagents that have the ability to trap the target pollutant from the gas stream and thus turning a gaseous sample into an aqueous sample. The wet test methods of interest here are the California Air Resources Board (CARB) Method 430 (Method 430), the United States Environmental Protection Agency (USEPA) Compendium Methods TO-5 and TO- 11A, and USEPA SW-846 Method 0010.A recent environmental study was performed to evaluate air toxic emissions from stationary combustion sources (e.g. boilers) at a municipal wastewater treatment plant. Acrolein, an aldehyde, is formed as a product of incomplete combustion from the boilers. As part of the environmental study, acrolein emission factors for boilers burning natural gas and digester gas were developed from an extensive search of available information, including research reports and stack test data. Recent defensible data collected during this search process indicated that the acrolein emission factors routinely reported in the literature are suspect due to concerns about the accuracy of sampling methods. The data showed that though acrolein concentration in emissions may be in the one to twenty parts per billion by volume (ppbv) range, the test methods most commonly used in the determination of acrolein were unable to quantify acrolein at those levels. It was also found that the lowest detection limits provided by various alternative sampling/analytical methods used to determine emissions from stationary sources for aldehydes and ketones is 50 ppbv for acrolein. This means that many sources with concentrations of acrolein below the detection limits would be reported as not detected. Since reliable monitoring data are not available, it cannot be determined whether ambient concentrations are in compliance with their ambient health-based standards. To address this issue, this paper will consider the pros and cons of alternative testing methods used in the sampling and analysis of acrolein from combustion sources.