The use of hydraulic fracturing for production of petroleum and natural gas has increased dramatically in the past decade, but the environmental impacts of this technology remain unclear. Experiments were conducted to quantify airborne emissions from 12 samples of hydraulic fracturing flowback wastewater collected in the Permian Basin, as well as the photochemical processing of these emissions leading to the formation of particulate matter (PM). The concentration of total volatile carbon (hydrocarbons evaporating at room temperature) averaged 29 mg of carbon per liter. After photochemical oxidation under high NO x conditions, the amount of organic PM formed per milliliter of wastewater evaporated averaged 24 μg; the amount of ammonium nitrate formed averaged 262 μg. Based on the mean PM formation observed in these experiments, the estimated formation of PM from evaporated flowback wastewater in the state of Texas is in the range of estimated PM emissions from diesel engines used in oil rigs. Evaporation of flowback wastewater, a hitherto unrecognized source of secondary pollutants, could significantly contribute to ambient PM concentrations.