This report is part of a project to characterize cotton gin emissions using stack sampling. In 2006, the Environmental Protection Agency (EPA) finalized and published a more stringent standard for particulate matter with nominal diameter less than or equal to 2.5 µm (PM2.5). This created an urgent need to collect additional cotton gin emissions data to address current regulatory issues. Current EPA AP-42 cotton gin PM2.5 emission factors did not exist prior to this point. The objective of this study is the development of PM2.5 emission factors for cotton gin first-stage mote systems based on the EPA-approved stack sampling methodology, Method 201A. The project plan included sampling seven cotton gins across the Cotton Belt. Five of the seven gins were equipped with first-stage mote systems where the exhaust airstream was not combined with a second-stage mote system. In terms of capacity, the five gins were typical of the industry, averaging 27.5 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 and/or ≤ 2.5 µm samples. This larger lint material can impact the reported emissions data, but EPA Method 201A does not suggest methods to account for these anomalies. Average measured first-stage mote system PM2.5 emission factor based on the five tests (14 total test runs) was 0.0041 kg/227-kg bale (0.0090 lb/500-lb bale). The first-stage mote system average emission factors for PM10 and total particulate were 0.023 kg/bale (0.051 lb/bale) and 0.032 kg/bale (0.071 lb/bale), respectively. The first-stage mote system PM2.5 emission rate from test averages ranged from 0.026 to 0.19 kg/h (0.057-0.43 lb/h). System average PM10 and total particulate emission factors were lower than those currently published in EPA AP-42. The ratios of first-stage mote system PM2.5 to total particulate, PM2.5 to PM10, and PM10 to total particulate were 12.7, 17.9, and 70.8%, respectively.