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 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. Also, some commonly used cotton gin systems were not represented or were combined with another system under a single emission factor in AP-42. No EPA AP-42 emission factors were published for 1st stage lint cleaning systems. The objective of this study was to collect PM10 emission factor data for 1st stage lint 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. Four of the seven gins were equipped with 1st stage lint cleaning systems where the exhaust airstreams were not combined with 2nd stage lint cleaning systems. In terms of capacity, the four gins were typical of the industry, averaging 28.1 bales/h during testing. Some 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 1st stage lint cleaning system average emission factors for PM10 and total particulate were 0.041 kg/227-kg bale (0.091 lb/500-lb bale) and 0.066 kg/bale (0.146 lb/bale), respectively. System average PM10 and total particulate emission factors were lower than those currently published in EPA AP-42 for 1st and 2nd stage lint cleaning systems combined. The 1st stage lint cleaning system PM10 emission rate test averages ranged from 0.26 to 2.92 kg/h (0.58-6.44 lb/h). The ratio of 1st stage lint cleaning system PM10 to total particulate was 62.3%.