Volume 1 Chapter 2: Emissions and concentrations of radiatively active atmospheric trace constituents

Radiatively active atmospheric trace constituents consist of the following groups of compounds: long-lived greenhouse gases with residence times of years, subject to international conventions; short-lived gases formed in the atmosphere from precursor compounds, remaining in the atmosphere for hours or days: notably ozone; and aerosols, that is, airborne particles interacting with short-wave radiation with both direct and indirect effects. The "direct effect" covers scattering or absorption of light, while the "indirect effect" describes the particles. contribution to cloud formation and their resulting influence on reflecting sunlight. This chapter covers these quite diverse compounds with respect to their relevance for Austria. The Austrian national greenhouse gas inventory demonstrates the importance of the energy sector for emissions of the long-lived greenhouse gases. Out of the total emissions, 79% are considered energy related (of which about one third is due to road transport, and a quarter describes energy use from industry), 13% are derived from industrial processes, and 9% from agriculture. Carbon uptake in forest biomass represents a sink of a few percentage points of total emissions. Variations of emissions have occurred since 1990, but no trends are seen for most sectors. A strong increase in transport emissions and a simultaneous decline of the forest sink at the same time has resulted in an overall increase of the Austrian greenhouse gas emissions of 19% over the last 20 years. Variations in Austrian emissions do not notably affect the results of measurements at Sonnblick Observatory, where concentrations of the greenhouse gases carbon dioxide and methane reflect the global situation. A relationship between emissions and concentrations only becomes evident for short-lived compounds. Reducing the emissions of precursors helped decrease ozone concentrations while the regional background has remained constant. Furthermore, the emissions and concentration