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Dr Pete Edwards from the National Centre for Atmospheric Science has carried out research into the chemical processes that occur in the night-time atmosphere in Southeast U.S. He found that the atmosphere is in a state of transition. In the past, the levels of pollutants in the air were dependent on the amount of nitrogen oxides, but now the atmosphere is becoming less controlled by nitrogen dioxides and therefore more similar to a pre-industrial atmosphere.

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Nitrogen oxides are emitted from human activities, such as combustion and power generation, and can interact with other compounds to create pollutants in our air such as ground-level ozone. Although emissions of nitrogen oxides have decreased significantly in the Southeast U.S over recent years, the reduction of pollutants has not followed the same trend. Scientists were curious to uncover why this might be the case. One possible reason is the highly understudied chemistry of the atmosphere during the night.

Dr. Edwards used measurements from research aircraft flights and models to find out about the chemistry of the Southeast U.S atmosphere at night. Because the atmosphere is becoming less controlled by the amount of nitrogen oxide in the air, Pete has suggested that trends in secondary pollutions will change in the future if nitrogen oxide emissions continue to decrease. His findings will change how we understand trends in secondary pollutants such as organic aerosols and ground-level ozone.

Pete Edwards, who is based at the University of York, has also investigated the role of nitrogen oxides in daytime atmospheric composition. To find out more about daytime atmospheric chemistry, you can read Pete's study on ozone pollution in Nature.

Edwards, P. M.; Aikin, K. C.; Dube, W. P.; Fry, J. L.; Gilman, J. B.; de Gouw, J. A.; Graus, M. G.; Hanisco, T. F.; Holloway, J.; Hübler, G.; Kaiser, J.; Keutsch, F. N.; Lerner, B. M.; Neuman, J. A.; Parrish, D. D.; Peischl, J.; Pollack, I. B.; Ravishankara, A. R.; Roberts, J. M.; Ryerson, T. B.; Trainer, M.; Veres, P. R.; Wolfe, G. M.; Warneke, C.; Brown, S. S.; Transition from high- to low-NOx control of night-time oxidation in the southeastern US. Nature Geoscience, 10 (7) , 490–495, [doi:10.1038/ngeo2976] Jun 2017