The dependence of open field burning emissions and plume concentrations on meteorology, field conditions and ignition technique

Abstract

A program of field and laboratory measurements of emissions from the burning of agricultural residues (primarily cereal straw and stubble) and plume behavior is described. Relationships investigated include the dependence of total emissions and plume concentrations on fuel management, field ignition technique and ambient meteorological conditions. Total particulate emissions (by mass) were found to increase strongly with increasing residue moisture content but are reduced to one half through the use of a backfire field ignition technique versus the head fire ignition method. Increased emissions from headfires is attributable to smoldering in the burned over areas. Backfire fuel consumption rates are typically about one-fifth that for headfires, resulting in a further reduction of particle concentrations in backfire plumes. Increased fuel loading reduces emissions, especially for headfires. The mass median diameter of particles from either fire ignition technique is less than 0.2 μm and in the average about one half of these particles are chloroform soluble. CO and gaseous hydrocarbon emissions were also found to be directly proportional to residue moisture content, but independent of field ignition technique. Plume rise is maximized (ground level concentration minimized) by using headfires in light winds (<4 m s −1). At higher wind speeds, limited plume rise and increasing fumigation increases ground level concentrations but this can be minimized through the use of backfires. As the effluent plume ages, the size spectrum shifts to smaller diameters suggesting significant evaporation with time. The results of fuel drying studies and cost analyses for the various techniques are also presented.