Estimating the Bowen Ratio for Application in Air Quality Models by Integrating a Simplified Analytical Expression with Measurement Data

Abstract

n air quality models, daytime sensible and latent heat fluxes are important factors that influence atmospheric stability. These heat fluxes originate from heat that is generated from solar radiation and is then released from the earth?s surface. Different climates and surface conditions may lead to varying heat flux distributions. Because latent heat flux is influenced by both solar radiation and plant evapotranspiration, it is often difficult to estimate. The objective of this study was to apply thermodynamic concepts to determine an equation that could be used to estimate the Bowen ratio in the absence of latent and sensible heat fluxes. This study showed that, using two meteorological parameters (i.e., absolute temperature and relative humidity), the Bowen ratio for the climate in Taiwan could be obtained and then used to estimate sensible and latent heat fluxes in a series of equations. Furthermore, the approach?s applicability was determined by testing the sensitivities of parameters used in the Bowen ratio equation. A comparison of results determined through the Priestly?Taylor and Penman?Monteith methods with meteorological data for Yilan and Chiayi counties, Taiwan, for the 2006 summer and winter is performed. The results of this study showed that, among the simulated latent heat fluxes in the two study areas, the values estimated using the Penman?Monteith method were the largest, followed by those estimated using the Priestly?Taylor method. Values estimated using the Bowen ratio method were the smallest. Predictions generated by the proposed Bowen ratio equation correlated with those generated by the other models; however, the values estimated with the Priestly?Taylor method were closest to the simulated values.