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 unloading 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. Three of the seven gins had unloading systems that used pneumatic conveyance and had exhaust airstreams that were not combined with another system. In terms of capacity, the three gins were typical of the industry, averaging 26.1 bales/h during testing. Some test runs were excluded from the test averages because they failed to meet EPA Method 201A test criteria. Also, other test runs, included in the analyses, had cotton lint fibers that collected in the ≤ 10 µm samples. This larger lint material can affect the reported emissions data, but EPA Method 201A does not suggest methods to account for these anomalies. The unloading system average emission factors for PM10 and total particulate were 0.107 kg/227-kg bale (0.237 lb/500-lb bale) and 0.131 kg/bale (0.289 lb/bale), respectively. The system average PM10 emission factor was higher and the system average total particulate emission factor was about the same as those currently published in EPA AP-42. Unloading system PM10 emission rate test averages ranged from 1.16 to 3.99 kg/h (2.57-8.79 lb/h). The ratio of unloading system PM10 to total particulate was 81.9%.