In the upper atmosphere, the ozone layer protects life on Earth from intense radiation from the sun. But in the troposphere close to the Earth it has harmful effects on humans and damages plants and crops. An important component of air pollution, nitrogen oxides cause the brown color in the pollution cloud seen over so many cities. To map chemical distributions, Emmons compiled data from 28 field research campaigns, then sorted data by season and altitude to make climatologies. The climatologies showed where measurements were lacking that, were they obtained, could answer questions about photochemistry and tropospheric nitric oxide production and transport, and consequently ozone production, Emmons says.
Current measurements are still far from providing a global view of nitrogen oxide distributions.
Some of the most obvious gaps are over Europe, Asia, Australia and the polar regions. She found generally good, if rough, agreement of various global climate models with observed concentrations of total reactive nitrogen species. Many points of disagreement between various computer model predictions were over areas in which there were data gaps, she says, making interpretation difficult. None of the models, she said, were either always lower or always higher than other models in their predictions. Because all of the models are so different, much more detailed study is required to understand them.