Predicting Electrically Generated Hydrogen Oxides From Ultraviolet Radiation Emissions

Abstract

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 investigated using ultraviolet (UV) measurements to determine LOH production. This laboratory study measured the spectra, UV fluxes at 185 nm, 254 nm, and 337 nm, OH, the hydroperoxyl radical (HO ₂ ), and the nitrogen oxides (NO _x ) generated by lightning and corona discharges to determine if useful relationships exist between UV and OH, HO ₂ , or NO _x . The experiments were conducted for different water vapor mixing ratios, pressures, and discharge intensities. For sparks, spark discharge properties appear to complicate the relationships between UV and OH, HO ₂ , or NO _x , although the complications will likely be resolved once these properties are better understood. For corona discharges, OH and HO ₂ are linearly correlated with UV at all three tested wavelengths. Thus, measuring UV radiation can be used to determine OH and HO ₂ production in the field.