ABSTRACT
This chapter focuses on the recent progress made in knowledge about emission sources and sinks at various spatial and temporal aggregation levels in general. Modelling may refer to estimating emissions of specific complex source categories, e.g. natural sources or delayed emissions, or to estimation of source strengths by inverse modelling using air concentration measurements and a priori emissions inventories as input. Inventory construction can focus on a specific year or on estimating multi-year historical trends. Many of the natural emissions inventories are thus the result of modelling of the underlying processes using these global datasets. The latter is defined as the total amount of trace gas in the atmosphere and related reservoirs, usually just the troposphere and the stratosphere. The sink strength of long-lived gases can be derived from can be derived from a combination of atmospheric observations, laboratory experiments and models.
