Coagulation is also important for size-distribution evolution as it reduces particle number and shifts the distribution to larger sizes. Coagulation rates are proportional to the square of the particle number concentration (all else remaining fixed), so the high number concentrations in biomassburning plumes relative to background can lead to rapid coagulational growth of the size distribution.The coagulation rate is therefore also affected by the rate of plume dilution (through a reduction in number concentrations, or N), itself a function of plume size and meteorological conditions. The rate and magnitude of the aerosol growth caused by these combined processes are functions of aging time, emission source characteristics, aerosol properties at emission, and atmospheric conditions.