Title: Source sampling of particulate matter emissions from cotton harvesting - system design and evaluation Authors
|Parnell, JR., C - TEXAS A&M UNIVERSITY|
|Shaw, B - TEXAS A&M UNIVERSITY|
|Capareda, S - TEXAS A&M UNIVERSITY|
|Lacey, R - TEXAS A&M UNIVERSITY|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2008
Publication Date: January 25, 2009
Citation: Wanjura, J.D., Parnell, Jr., C.B., Shaw, B.W., Capareda, S.C., Lacey, R.E. 2009. Source sampling of particulate matter emissions from cotton harvesting - System design and evaluation. Applied Engineering in Agriculture. 25(1):85-96. Interpretive Summary: Agricultural producers are facing increased pressure from air pollution regulators due to poor regional air quality and the use of inaccurate emission factors. Limited work on measuring particulate matter emissions from cotton harvesting has been conducted. The work on which the current particulate matter emission factors for cotton harvesting are based utilized indirect techniques which contain significant levels of uncertainty. An indirect technique employs a mathematical dispersion model to back calculate emission factors from particulate matter concentrations and meteorological data measured downwind of the harvesting operation. It was hypothesized in this work that the emissions from cotton harvesting operations can be measured more accurately on a direct basis. Therefore, the objective of this work was to document the design and evaluation of a system designed to measure emission concentrations onboard a six row cotton picker. The key functions of the sampler were to collect all of the seed cotton, air, and foreign material from one cotton transport duct on the harvester, separate the seed cotton from the air stream, and channel the particulate laden air stream through a duct where an emission concentration could be measured. The results indicated that the optimum seed cotton separation system design utilized a separator box design with a straight back wall and a 47 cm straight baffle angled at 52 degrees with the top of the separator box. Air velocity profile testing showed that the highest air velocity was at the center of the exit duct of the seed cotton separation system and the air velocity patterns were not affected by varying rates of seed-cotton flow. Isokinetic sampling showed that there was no significant difference between the duct average emission concentration and the emission concentration measured at the center of the duct. Particle size distribution (PSD) analyses indicated that the PM collected at the center of the exit duct adequately represented the duct average PSD. The findings of this work indicate that it is possible to measure emission concentrations onboard a modern six row cotton picker. The emission concentrations can be used to calculate emission factors that do not contain the uncertainty of previous estimates. Emission reduction regulations based on accurate emission factors will help producers avoid inappropriate fines, fees, and increased production costs resulting from regulatory actions based on inaccurate emission factors.
Technical Abstract: State and regional air pollution regulatory agencies are required by federal law to reduce ambient particulate matter concentrations in non-attainment areas to a level in compliance with National Ambient Air Quality Standards. All emission regulations, including reduction regulations, should be based on accurate emission factors. Agricultural particulate matter emission factors are difficult to quantify due to the nature of the emission source, size characteristics of the dust, and environmental factors affecting natural dispersion of the pollutant. Cotton harvesting emission factors developed through previous efforts using indirect techniques employing ambient sampling and dispersion modeling contain substantial levels of uncertainty due to these factors. It was hypothesized that particulate matter emissions from cotton harvesting could be more accurately quantified through direct source measurement than with previously used indirect techniques. The objective of this work was to document the design and evaluation of a system designed to measure emission concentrations onboard a modern six row cotton picker. The principal functions of the system were to collect all of the seed cotton, air, and foreign material from one cotton transport duct on the harvester, separate the seed cotton from the air stream, and channel the particulate laden air stream through a duct where an isokinetic emission concentration could be measured. Optimization tests were conducted on the baffle separation section of the system to maximize the removal of seed cotton and large foreign material from the conveying air stream. Additional tests were conducted across the exit duct cross section to investigate air velocity profile and particulate matter concentration patterns. Maximum seed cotton removal was achieved with a straight back wall separator configured with a 47 cm baffle installed at a 52 deg with the top of the box. No differences in air velocity patterns across the duct were detected at varying rates of seed cotton flow and an isokinetic center point measurement adequately represented the duct average emission concentration and particle size distribution. The findings of this work indicate that it is possible to measure cotton harvester emissions on a direct basis at the source. Thus, resulting emission factors will not have the uncertainty contained in previous emission factors developed through indirect techniques.