Demand for ozone-depleting substances and hydrofluorocarbons estimated by a Tier 2 emission inventory model compared to top-down chemical consumption data for the US

Abstract

In preparing inventories of ozone-depleting substance (ODS) substitutes, primarily hydrofluorocarbons, the US employs models consistent with Tier 2 methodologies from the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The model calculates chemical consumption and emissions for 60 sub-applications, which are aggregated to five application levels. So-called “bottom-up” models require data and assumptions regarding the sub-application industries, including number of products introduced and retired each year, the type and amount of chemicals initially used, the emission pattern of the chemicals and if any released chemical is replaced. Once developed, the bottom-up model's estimates of chemical demand can be compared to “top-down” chemical consumption or sales. Combining these types of data gives a partial picture of the amount of ODS and substitutes introduced to the US economy. This paper examines the top-down data in comparison to the bottom-up estimates derived from the inventory models and discusses possible explanations for the differences noted.