Performance of a single-monochromator diode array spectroradiometer for the determination of actinic flux and atmospheric photolysis frequencies

The performance of a new spectroradiometer instrument based on a diode array technique during its first field deployment at the International Modeling and Measurement Intercomparison (IPMMI) has been evaluated. The instrument is a single-monochromator diode array spectroradiometer that was used to measure both actinic flux and derived values of j(O¹D) and j(NO₂). Spectra may be collected over the wavelength region λ = 280-450 nm at variable integration times (typically 1 s for normal operation), and data may be converted to actinic flux/photolysis frequencies using National Institute of Standards and Technology traceable calibration standards. The relative accuracy of these measurements is compared to photolysis frequencies derived using similar and contrasting experimental techniques. The instrument performed adequately in the comparison, but the problem of poor stray light rejection in the single monochromator has the potential to propagate significant errors in the derived photolysis frequencies. A full error analysis together with instrument characterization has been performed and is reported. The feasibility of using such instruments in the field for the measurement of atmospheric photolysis frequencies is also discussed.