Experimental determination of Rayleigh scattering cross-sections at 408 nm

Cavity ring-down spectroscopy (CRDS) has been applied to retrieve accurate Rayleigh scattering cross-sections, sigma(Rayl). for a set of atmospheric gases at similar to 408 nm. Step pressure changes and pressure ramps were used in three different but similar optical cavities to measure light extinction by N-2, O-2, Ar, CO, CO2, N2O, CH4 and synthetic air (SA). The experimentally determined sigma(Rayl). were compared with sigma(Rayl). values calculated for these atmospheric gases using knowledge of extrapolated literature values of the refractive index (n) and King correction factors measured in different spectral regions. The difference between measured and calculated sRayl. using the most recently published dispersion relationship for N2O and CH4 is similar to 0.6%. This confirms the improved accuracy of the new dispersion relationship. The calculated and measured sRayl. agreed on average within 0.6%, 2.4%, 1.2%, 2.2%, and 1.5% for the gases CO2, N-2 O-2, SA, and Ar at similar to 408 nm. However, for CO, the difference is 4.1%, i.e. more than twice the error. This implies that improved knowledge of the dispersion relationship for CO, and thus the refractive index and King correction factors, would be of value to calculate sRayl. in the blue spectral region.