Application of a Tracer Aerosol Technique Using Atomized Sodium Chloride Particles for Measuring Ventilation Rates in a Naturally Ventilated Azrom-Type Greenhouse in Zimbabwe

Abstract

In this study ventilation rates for a naturally ventilated Azrom-type greenhouse in Zimbabwe were determined by both a tracer aerosol technique using atomized NaCl particles as the tracer and an integrating nephelometer to monitor the decay of the aerosol particles' concentration in the greenhouse and the water vapor balance method. Comparison of the results showed that, although the tracer aerosol method suffers from some of the typical problems of tracer techniques in general (like the need for uniform concentration of the tracer), it gave comparable results with the water vapor balance method, while overcoming the difficulty of the water vapor balance of scaling up from single (or few) plant(s) to whole canopy transpiration. The M903 Radiance Research portable nephelometer is a lightweight, low-power instrument, and costs about US$7,000, while the nebulizer costs less than US$1,000. In comparison with the high cost of gas analyzers (up to US$30,000 for most CO2 and N2O analyzers) and the additional high costs and unavailability of the tracers, the method offers a cost-effective way of measuring ventilation rates in a greenhouse. For measuring leakage ventilation rates, however, the tracer aerosol technique failed to provide useful results.