This report is part of a project to characterize cotton gin emissions from the standpoint of stack sampling. The impetus behind this project was the urgent need to collect additional cotton gin emissions data to address current regulatory issues. A key component of this study was focused on Environmental Protection Agency (EPA) total particulate emission factors. EPA AP-42 emission factors generally are assigned a rating, from A (excellent) to E (poor), to assess the quality of the data being referenced. Current EPA total particulate emission factor ratings for cotton gins are extremely low. Cotton gin data received these low ratings because the data were collected almost exclusively from a single geographical region. The objective of this study was to collect additional total particulate emission factor data for 3rd stage seed-cotton cleaning systems from cotton gins located in regions across the cotton belt using EPA-approved stack sampling methodology. The project plan included sampling seven cotton gins. Key factors for selecting specific cotton gins included: 1) facility location, 2) production capacity, 3) processing systems, and 4) abatement technologies. Two gins with 3rd stage seed-cotton cleaning system exhausts were sampled. The average production rate during testing for the two gins was 21.0 bales/h. The average 3rd stage seed-cotton cleaning system total particulate emission factor based on two tests (six total test runs) was 0.023 kg/227-kg bale (0.052 lb/500-lb bale). This average total particulate emission factor was less than that currently published in 1996 EPA AP-42, which was 0.043 kg/bale (0.095 lb/bale). The 3rd stage seed-cotton cleaning system test average emission rates ranged from 0.27 to 0.75 kg/h (0.59-1.66 lb/h).