Region-Resolved Global Dust Transport

Abstract:

Currently the functionality required to directly track the transport of regionally tagged chemical species does not exist in global models as it does in select regional models. While some global models contain adjoint formulations that allow for the concentration sensitivities of a given region to be determined, this method does not show how pollution from a given region impacts all the areas around it. The closest that global models get to directly tracking regionally tagged species have primarily been through brute-force or zero-out applications, which tend to be either very limited in scope or have significant impacts on chemical reaction rates. Specifically the tagged species approach captures both the non-linear behaviors within the model, missed in the brute-force method, and the full scope of the chemical reactions, missed in the zero-out applications.

With the ability to easily tag pollutants based on their source region it becomes realistic to estimate the impacts that sub-continent scale regions can have on air pollution levels. Depending on the resolution of both the model and available population data, it is possible to use this functionality to estimate exposure resulting from region specific pollution.

In this study we have implemented a module within the GEOS-Chem 3-D atmospheric composition model that will allow for this type of flexible region tagging for non-reactive species as a step towards being able to track species point of origin through chemical reactions. Functionally this module behaves similarly to the Particulate Matter Source Apportionment Technology (PSAT) feature within the Comprehensive Air Quality Model with Extensions (CAMx) which tracks the species utilizing the various fluxes in each grid cell in the model.

Utilizing this module we have divided the sub-Saharan into several distinct regions in order to track how dust from each region is transported around the globe. The results are compared to identify regional differences in how sub-Saharan dust from different regions is transported both regionally and globally. Furthermore we discuss how this data compares to satellite observations of sub-Saharan dust transport and the insights garnered through this comparison.