Particulate matter concentrations were measured upwind and downwind of cotton harvesting operations in three locations in Texas. A state of the art six row picker and an older two row picker were used in the field tests. A novel source sampling system was used to collect source concentration measurements from the six row machine. The upwind/downwind concentrations and meteorological data collected onsite were used in a dispersion model to back calculate the emission rates from the harvesting operation. A comparison of the emission factors determined from both machines is included. An analysis of the emissions data will be performed to determine if it is more appropriate to report cotton harvesting emission factors on a mass of PM per area harvested or mass of PM per mass of cotton harvested basis.