The decline of the manufacturing base in Western Europe and North America over the last few decades, along with the rapid collapse of the Soviet Union, has resulted in a substantial reduction in the net flux of pollutants which are emitted from industrial practices for such regions. This source has now been eclipsed by other economic sectors, where the rapid growth in transport due to the increased global movement of both goods and people has resulted in this sector becoming one of the most dominant sources of trace gas emissions.

There is the added complication in that more and more emissions are being injected into the middle troposphere (~10km), which have a disproportionate effect due to the state of the atmosphere at such altitudes. This has subsequently changed the nature of the most dominant emissions, where the release of (e.g.) sulphur dioxide (SO2) from power plants has been replaced by the release of (e.g.) nitrogen dioxide (NO2) from motor vehicles. These two chemical species have markedly different effects on the composition of the atmosphere, where SO2 is predominantly washed out of the system (acid rain) whilst NO2 forms ozone (O3) under the action of sunlight, which acts as an irritant and potent greenhouse gas. Moreover, for regions such as China and India there is a "double whammy" in that both industrial and transport emissions have increased simultaneously over a relatively short period of time. To address this question the EU-QUANTIFY project has the specific task of assessing how the changing transport sector is likely the affect the global troposphere, both for the present and into the future. One scientific tool used for assessing the consequences of these shifting emission patterns are large-scale global chemistry transport models. By applying estimates for the emissions which are expected from the different transport sectors (namely road, air and sea) scientists at KNMI have been involved in an international experiment to determine which of these transport methods causes the most noticeable effects on tropospheric O3 by reducing the total emissions introduced by each transport sector by %5 in a cumulative and stepwise manner. As a result of the global distribution of each transport sector, and the magnitude of the emissions introduced, it was found that shipping has the largest effect, followed by road transport then aircraft. The figure below shows the changes in tropospheric O3 as a result of reducing the emission from each sector in a step-wise manner for January and July, 2003. As would be expected the emissions from ships effect the lower troposphere whilst those from aircraft the upper troposphere. Surprisingly, the emissions from road transport have a marked effect in the upper troposphere, where these emission occur on land which exhibits strong convective mixing thus introducing vertical transport of the effects. Future experiments aim to apply the emission estimates for 2025 and 2050 to determine the consequences changing human behavior will have on the future atmosphere.

Results were recently published in ACP.