Currently there are no international obligations regarding the temporal distribution of emissions. International obligations and reviews are in place for emission inventories and for the spatial distribution of emissions. Hence, these have been subject to significant improvements over the last decades, and efforts to both quantify and reduce the uncertainties have been undertaken. However, similar efforts have not been devoted to the temporal resolution of emissions. Temporal resolution of emissions have a significant impact on the match between modelled and measured air pollution levels, in particular when applying atmospheric transport models with high spatial resolution on a national or local scale. The temporal factor has a large impact on the dispersion, due to variations in climatic parameters like wind speed, wind direction, temperature, and precipitation, and thereby on the human exposure.

Temporal variations in emissions occur both on monthly, daily and hourly basis based on production, use and transport patterns. The time factors will be highly variable from emission source to emission source and variability can also be expected between pollutants.

The temporal model will include temporal distribution profiles on monthly, daily and hourly level. The emission source aggregation level in the temporal model will depend on the availability of statistical data with a temporal component. A number of statistics are available on monthly basis, but temporal data on daily and hourly level are generally scarce, and it might be necessary to use data for smaller areas, from other countries, use proxy data or base the temporal profiles on expert judgement.