A field study on grass field burning was conducted in the Willamette Valley of Oregon during the summer of 1965. Approximately 230,000 acres of grass field are burned in the valley during August and September. Serious air pollution problems result from this burning. The purposes of the study were to determine the effect of environmental variables on grass field burning and to determine if conditions exist when significant air po11ution reduction can be achieved. The environmental variables investigated were time from harvest to burning, time of day, air temperature, relative humidity, soil and straw moisture, wind speed and direction, and fuel density. The dependent variables measured torn particulate emission and size distribution, combustion temperature, burn rate, amount of ash, percent of organics in the particulate, and smoke appearance.The results were analyzed statistically to determine the significant variables and their relationship.