|Parnell, Jr., Calvin|
Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/30/2003
Publication Date: 7/30/2003
Citation: Buser, M.D., Parnell, Jr., C.B., Shaw, B.W., Lacey, R.E. 2003. Characteristic particle size distribution for cotton gins: Based on the 1996 AP-42 Emission Factors. American Society of Agricultural Engineers. Paper No. 034113. Interpretive Summary: Agricultural operations are encountering difficulties complying with the current air pollution regulations for particulate matter (PM). The regulations are based on the National Ambient Air Quality Standards (NAAQS), which set maximum limits for ambient PM based on protecting public health. PM is currently regulated in terms of particle diameters less than or equal to a nominal 10 micrometers (PM10). Compliance with the PM regulations may be determined through dispersion modeling. Modeling requires emission rates which are determined from EPA's list of emission factors or from source sampling. Emission factors are industry specific. PM10 emission factors are typically determined from source sampling based on EPA's Method 201a sampling protocol. Ultimately, this method would produce an accurate measure of PM less than or equal to 10 micrometers. However, this method uses a cyclone to separate the smaller particles from the larger particles and the cyclones are not perfect. Errors are introduced due to the interaction of the particle size and cyclone performance characteristics. Two theoretical methods were introduced to estimate the true PM10 emitted from cotton gin process streams. These estimates show that cotton gins are being forced to comply with more stringent PM regulations than urban type sources. The bottom line is that regulatory agencies are using sampling methods that introduce substantial errors when the samplers are exposed to larger dusts than they were designed to sample.
Technical Abstract: Agricultural operations across the United States are encountering difficulties in complying with the current air pollution regulations for particulate matter (PM). Cotton gins are most frequently regulated based on results obtained from dispersion modeling that utilize emission rates based on emission factors from EPA's 1996 AP-42 or emission rates derived from source sampling. PM10 emission factors are typically determined from source sampling based on EPA's Method 201a sampling protocol. Method 201a utilizes a cyclone in the sampling system to remove the larger particles and allow the smaller particles to penetrate to the filter. EPA has published limited information documenting the performance characteristics of the cyclones used in Method 201a. Recent research has shown that ambient PM10 samplers can over-estimate the true PM10 in the ambient air when the sampler is exposed to dust with a mass median diameter larger than 10 micrometers. The purpose of this manuscript is to explore the potential impacts associated with determining PM10 emission values for cotton gin exhausts using the EPA's Method 201a. Two theoretical methods were introduced to estimate the true PM10 emitted from process streams associated with cotton gins. The first method was based on defining particle size distributions for each individual process stream exhaust. The second method expanded the first method by defining an average weighted particle size distribution. Estimates from the first and second methods showed that the total true PM10 emission factors were about 28% and 26% lower than EPA's 1996 AP-42 total PM10 emission factor, respectively. The percent of true PM10, based on total PM10 and TSP emission factors determined by methods 1 and 2, were 28% and 29%, respectively; whereas the current EPA 1996 AP-42 defined estimate of the percent PM10 is 39%. Therefore, when cotton gins are regulated based on PM10 emission factors from AP-42 or emission factors derived from EPA's Method 201a source sampling procedures, the cotton gins are being force to comply with more stringent PM regulations than urban type sources. The bottom line is that regulatory agencies are using sampling methods developed to regulate urban sources to regulate agricultural sources, and these methods introduce substantial errors when the mass median diameter of the dust being emitted is larger than 10 micrometers.