Development and Evaluation of Portable Reduced-Complexity Air Quality Models for Policy Assessment in Africa

 Atmospheric models serve an essential role in guiding air pollution management by  assessing health impacts from various sources. In the US and other developed nations,  chemical transport models (CTMs) are used to predict pollutant concentrations and to  evaluate compliance with air quality standards. CTMs are state-of-the-science models  but are resource-intensive requiring skilled technical personnel, limiting their use in  many policy applications, particularly in developing countries. Reduced-complexity  models (RCMs) were developed to address those limitations; they apply simpler  chemistry, are easier to use, require fewer and simpler inputs, are faster than CTMs,  and can assess more policy scenarios. However, most RCMs to date are limited in  scope to the United States, but there are many countries with higher pollutant  concentrations and limited resources to manage air pollution. To address this need, we  present the Rapid Estimation of Air Concentrations for Health (REACH), a location agnostic Gaussian plume model with chemistry that predicts PM2.5 concentrations and is  easily portable to any region of the globe. Here we report the development of REACH  and its evaluation in the United States against ambient measurements and other RCMs.  One important output of REACH are estimates of marginal social costs, which are the  total mortalities downwind from a source location caused by emitting an additional tonne  of a PM2.5 precursor. For the US, REACH estimates average marginal social costs for  2005 ground PM2.5, SO2, NOx, NH3, and VOCs as 142, 73, 10, 73, and 11 $/ktonne,  respectively. We demonstrate that the REACH marginal social costs are generally  comparable to AP2, EASIUR and InMAP RCMs with R2 ranging from 0.38-0.77  depending on the PM2.5 species. REACH is open-source and aims to aid in air quality  decision-making in the US and internationally and to serve as a point of comparison  with other RCMs.