The Parameters Estimation for a PM2.5Transport Model with the Adjoint Method

Daosheng Wang,Xianqing Lv,Ning Li,Youli Shen

doi:10.1155/2016/9873815

Daosheng Wang, Xianqing Lv + Show 2 more

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https://doi.org/10.1155/2016/9873815

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Abstract

Based on the theory of inverse problem and data assimilation, the adjoint method is applied for the estimation of parameters including the initial condition (IC), the source and sink (SS) in a PM2.5transport model. To reduce the ill-posedness of the inverse problem, an independent point scheme (IPS) is implemented during the estimation process. In twin experiments, both the prescribed IC and SS can be inverted successfully and better inversion results are obtained when the IPS is used than not, suggesting the feasibility and validity of the PM2.5transport model as well as the IPS. In practical experiments, several inversion strategies are compared based on the simulation results of PM2.5concentrations over China. It is found that IC and SS are better estimated with smaller difference between simulated results and observations, when IC and SS are inverted simultaneously than separately. And the simulated results can reproduce the temporal and spatial variation feature of the observed PM2.5concentrations. On the basis of the numerical results, it is shown that the adjoint method and the IPS are the powerful way to improve the precision of the simulation of the PM2.5concentrations.

Highlights

In China, a combination of rapid industrialization and high population density inevitably deteriorates the air pollution problems [1]
It could be found that in PE1 the cost function which is normalized by its initial values at the first iteration step reaches the minimum value and the mean absolute errors (MAEs) between simulated values and observations in “assimilated cities” is the smallest of the practical experiments (PEs) using independent point scheme (IPS)
It is shown that when the initial condition (IC) and the source and sink (SS) are inverted simultaneously with or without IPS, the effect of the data assimilation is the best

Summary

Introduction

In China, a combination of rapid industrialization and high population density inevitably deteriorates the air pollution problems [1]. The parameters of a PM2.5 transport model are estimated using the adjoint method (i.e., 4D-Var) with the IPS and the PM2.5 concentrations are simulated over China. An IPS is developed in this paper In this scheme, some grid points are selected uniformly in the space domain as independent points at which the values of parameters are adjusted and the values at other points are obtained by the interpolation of the values at the independent points. With the PM2.5 transport model and corresponding adjoint model constructed, the PM2.5 observations could be assimilated to optimize the parameters with IPS and improve the simulated results by repeating the following steps. The wind data are derived from the National Centers for Environmental Prediction (NCEP) winds daily averaged for each 2.5∘ latitude by 2.5∘ longitude region

Twin Experiments

Practical Experiments

Summary and Discussion