Evaporation itself is driven by local conditions; because these conditions vary with location, evaporation rates and efficiency of operation differ. Thus, drier climates generally favor evaporation as a waste management tool. An onsite operator reported that the nozzles were quite effective in speeding up evaporation: "We just spray those droplets of water into the air and the contaminants evaporate more quickly." The rate of evaporation or condensation is directly proportional to the magnitude of those vapor pressure differences. In semiarid regions, evaporation is much more common than condensation, and the very term "semi-arid" suggests that evaporation usually proceeds at a fairly rapid rate. If evaporation is to continue, the surface air layer must be constantly removed and replaced with unsaturated air. In pond, pit, and lagoon management, knowledge of evaporative processes is important to the environmental professional in understanding how water losses through evaporation are determined.