This report is part of a project to characterize cotton gin emissions from the standpoint of stack sampling. In 2006, the Environmental Protection Agencey (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, because current EPA AP-42 cotton gin PM2.5 emission factors did not exist. The objective of this study was the development of PM2.5 emission factors for cotton gin second-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 had second-stage mote systems where the exhaust airstreams were not combined with first- stage mote systems. In terms of capacity, the five gins were typical of the industry, averaging 30.0 bales/h during testing. Some test runs were excluded from the test averages because they failed to meet EPA Method 201A Test criteria. Also, during other test runs, included in the analyses, cotton lint fibers were 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 second-stage mote system PM2.5 emission factor based on the five tests (11 total test runs) was 0.0025 kg/227-kg bale (0.0055 lb/500-lb bale). The second-stage mote system average emission factors for PM10 and total particulate were 0.010 kg/bale (0.022 lb/bale) and 0.013 kg/bale (0.029 lb/bale), respectively. The second-stage mote system PM2.5 emission rate from test averages ranged from 0.038 to 0.13 kg/h (0.084-0.28 lb/h). System average PM10 and total particulate emission factors were lower than those currently published in EPA AP-42. The ratios of second-stage mote system PM2.5 to total particulate, PM2.5 to PM10, and PM10 to total particulate were 19.1, 25.0, and 76.6%, respectively.