An Undergraduate Experiment to Investigate Air Pollutants Created from Lightning

Abstract

Chemistry of the environment has been a long-standing and important area of scientific research. Atmospheric chemistry is of particular interest in society due to the impact that rising levels of pollutants are having on the climate. It is well-known that combustion processes create CO and NOx, which leads to the creation of other pollutants, such as ozone and CO2. There are natural processes, such as lightning, that also create a significant amount of pollutant gases. The purpose of this guided and open inquiry laboratory experiment is to provide an opportunity for students to investigate how lightning may produce pollutant gases in the atmosphere. In the guided inquiry experiment, a sealed IR gas cell containing air is exposed to a spark or corona discharge created by an Oudin coil to mimic lightning. IR spectroscopy is used to monitor the reaction progress and identify new species made after exposure to the electrical discharge. Based on the results, students draw conclusions about what types of gases are created in the two different discharge processes and how lightning may contribute to atmospheric pollutants. Students move on to the open inquiry to further investigate aspects of atmospheric gases, where they develop their own hypothesis and methods based on one of the provided suggestions, such as the effect of spark and corona discharge on pure oxygen, nitrogen, or carbon dioxide gases, the kinetics of ozone creation and decay, and the temperature dependence of NO2 dimerization. Although designed for an honors general chemistry course, this experiment can be adapted for second-semester general chemistry, environmental chemistry, analytical, and physical chemistry laboratory courses. Results from these experiments are presented, and the relevant atmospheric chemical processes are discussed. The impact of this experiment on perceived gains in knowledge, the value of inclusion in the curriculum, and the design of the experiment were assessed, and the results are discussed.