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 EPA emission factors for particulate matter with a particle diameter nominally less than or equal to 10 µm (PM10). The 1996 EPA AP-42 emission factors were assigned quality ratings, from A (Excellent) to E (Poor), to assess the quality of the data being referenced. Emission factor quality ratings for cotton gins were extremely low. Cotton gin data received these low ratings because they were collected almost exclusively from a single geographical region. The objective of this study was to collect additional PM10 emission factor data for 3rd stage seed-cotton cleaning systems at cotton gins located in regions across the cotton belt based on EPA-approved stack sampling methodology, Method 201A. The project plan included sampling seven cotton gins across the cotton belt. Key factors for selecting specific cotton gins included: 1) facility location, 2) production capacity, 3) processing systems and 4) abatement technologies. Two of the seven gins were equipped with 3rd stage seed-cotton cleaning systems. In terms of capacity, the two gins were typical of the industry, averaging 22.0 bales/h during testing. The 3rd stage seed-cotton cleaning system average emission factors for PM10 and total particulate were 0.019 kg/227-kg bale (0.042 lb/500-lb bale) and 0.024 kg/bale (0.054 lb/bale), respectively. The system average PM10 emission factor was higher and the system average total particulate emission factor was lower than those currently published in EPA AP-42. Third stage seed-cotton cleaning system PM10 emission rate test averages ranged from 0.28 to 0.56 kg/h (0.61-1.24 lb/h). The ratio of 3rd stage seed-cotton cleaning system PM10 to total particulate was 79.1%.