American Chemical Society
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A Fluence-Based Method for the Direct Comparison of Photolysis Kinetics under Variable Light Regimes

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posted on 2015-07-14, 00:00 authored by Maya L. Wei-Haas, Yu-Ping Chin
Chemical actinometers are traditionally used to account for photochemical experiments conducted under different light regimes (simulated vs natural; also seasonal, daytime, cloud cover, and latitude changes). Their many limitations and the lack of a universally applicable actinometer demand development of a new approach for studying environmentally relevant photochemical processes in sunlight. We suggest the use of fluence-based rate constants (converted to time-based rate constants and half-lives with irradiance normalization), using a data-logging radiometer to track the accumulated dose of UVA and UVB radiation. Our results suggest that this method can effectively account for minor changes in cloud cover and sun angle in the photolysis of p-nitroanisole/pyridine and p-nitroacetophenone/pyridine. The greatest error is caused by factors (e.g., dense cloud cover, extreme sun angles, and changes in ozone) that affect relative UVA and UVB fluence. We believe that this simple and elegant method serves as an important bridge between laboratory and field-based environmental photochemistry experiments.