Satellite observations are providing important new information about global nitrogen oxide (NOx) emissions. 

Lyatt Jaeglé and colleagues from the University of Washington, US, used new satellite observations from the Global Ozone Monitoring Experiment instrument onboard the European Space Agency's ERS-2 satellite. They used the observations to overcome uncertainties associated with current NOx emission inventories.   

The wide range of different statistics about NOx sources such as fuel and land use, agricultural data, and estimates of burned areas are usually gathered in a 'bottom up' approach and are often unreliable. 

Jaeglé's analysis of the satellite observations, presented at a recent Faraday Discussion meeting on atmospheric chemistry, shows that fuel combustion dominates NOx emissions at northern mid-latitudes, while fires are a significant source in the Tropics.   

She also discovered a larger than expected role for soil emissions, especially over agricultural regions where fertilisers are used heavily. 

The spatial and seasonal distribution of each NOx source can be clearly mapped from space. This allowed the team to provide independent 'top down' data on individual NOx sources and helped resolve the discrepancies in existing inventories.   

Jaeglé is sure where future challenges lie. 'Over the last few years, new satellite instruments probing the composition of our lower atmosphere have been revolutionising atmospheric chemistry,' she said. 'The challenge is to use these new global observations to understand and predict the effects of human activities on atmospheric composition, and thus on human health and ecosystems.'   

Philip Earis