Source Sampling of Particulate Matter Emissions from Cotton Harvesting – System Design and Evaluation

摘要

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 ° 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