Predicting Electrically Generated Hydrogen Oxides from Ultraviolet Radiation Emissions

Electrical discharges such as lightning and corona discharges generate extreme amounts of hydroxyl radical (OH), the atmosphere’s most important oxidizer, enough for electrical discharges to be a globally significant source of OH. However, there are few field measurements of electrically generated OH (LOH), hindering attempts to better understand the role of LOH in the atmosphere. Furthermore, instruments traditionally used for measuring OH cannot routinely measure LOH because these instruments are large, metal, and must be placed close to the discharge to detect short-lived OH, and are thus likely to either interfere with the electrical discharge or miss the LOH entirely. Instead, we propose measuring the ultraviolet (UV) radiation emitted by the electrical discharges and using these UV measurements to determine LOH production. In this laboratory study, the spectra, UV fluxes at three different wavelengths, OH, the hydroperoxyl radical (HO2), and the nitrogen oxides (NOx) generated by lightning and corona discharges were measured to determine if useful relationships existed between OH, HO2 or NOx and UV. The experiments were also conducted at different water vapor mixing ratios, pressures, and discharge intensities. The dependence of OH, HO2, NOx and UV on different spark discharge parameters complicates the relationship between these variables, but relationships between the chemical species and UV likely can be resolved with future work. However, OH and HO2 were found to be linearly correlated to UV in corona discharges, and this relationship can be used to determine OH and HO2 production in the field.