posted on 2015-07-14, 00:00authored byMaya 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.