A gradient-independent model of gas fluxes was formulated and tested. The model is built on the relationship between gas flux and the time history of surface gas concentration, known as half-order derivative (HOD), when the transport of the gas in the boundary layer is described by a diffusion equation. The eddy-diffusivity of gas is parameterized based on the similarity theory of boundary layer turbulence combined with the MEP model of surface heat fluxes. Test of the new model using in-situ data of CO2 concentration and fluxes at several locations with diverse vegetation cover, geographic and climatic conditions confirms its usefulness and potential for monitoring and modeling greenhouse gases. The proposed model may also be used for estimating other GHGS fluxes such as methane (CH4) and Water vapor flux. This proof-of-concept study justifies the proposed model as a practical solution for monitoring and modeling global GHGS budget over remote areas and oceans where ground observations of GHGS fluxes are limited or non-existent. One focus of the on-going research is to investigate its application to producing regional and global distributions of carbon fluxes for identifying sinks and sources of carbon and re-evaluating the regional and global carbon budget at monthly and annual time scales.

The goal of this study is to develop a gradient-independent method for modeling surface gas flux using surface gas concentration data. The proposed method is built on the relationship between gas flux and the time history of surface gas concentration, known as half-order derivative (HOD), when the transport of gas in the boundary layer is described by a diffusion equation. The new model is tested using in-situ data of CO2 concentration time series at half hour (or hour) intervals from Ameriflux Network at several locations in US, Canada, Mexico and Brazil to estimate CO2 fluxes. In this research the estimated CO2 flux using HOD method are compared with observed CO2 fluxes from four study sites out of 160+ sites with diverse vegetation cover, geographic and climatic conditions to test the generality of model within reasonable endeavor. The sites are Cedar Bridge National Forest, New Jersey, Delta Junction 1920 Control, Alaska, Lucky Hills Shrub land, Arizona, and LBA Tapajos Mature Forest, Brazil. The modeled CO2 flux demonstrates close agreement with field observations confirming the usefulness and potential of HOD model for estimating CO2 gas fluxes.