This report is part of a project to characterize cotton gin emissions from the standpoint of total particulate stack sampling and particle size analyses. In 2006 and again in 2013, the United States (U.S.) Environmental Protection Agency (EPA) published a more stringent National Ambient Air Quality 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 EPA AP-42 cotton gin PM2.5 emission factors were limited. In addition, current EPA AP-42 emission factor quality ratings for cotton gin PM10 (particulate matter with nominal diameter less than or equal to 10 µm) data are questionable, being extremely low. The objective of this study was to characterize particulate emissions for 2nd stage seed-cotton cleaning systems from cotton gins across the cotton belt based on particle size distribution analysis of total particulate samples from EPA-approved stack sampling methods. Average measured PM2.5, PM6, and PM10 emission factors based on the mass and particle size analyses of EPA Method 17 total particulate filter and wash samples from five gins (14 total test runs) were 0.0014 kg/227-kg bale (0.0031 lb/500-lb bale), 0.015 kg/bale (0.032 lb/bale), and 0.025 kg/bale (0.056 lb/bale), respectively. The 2nd stage seed-cotton cleaning system particle size distributions were characterized by an average mass median diameter of 12.2 µm (aerodynamic equivalent diameter). Based on system average emission factors, the ratio of PM2.5 to total particulate was 2.42%, PM6 to total particulate was 25.1%, and PM10 to total particulate was 43.2%.