ROx Radicals Research Articles

Optimized Operation and Calibration Procedures for Radical Amplifier-Type Detectors

Abstract Laboratory experiments were conducted to improve the operation and calibration procedures for the ambient ROx radical detectors (ROx = HO2 + RO2 + OH + RO) based on chemical amplification. A new method for the experimental determination of the effective ratio between the absorption cross sections for water and molecular oxygen at 184.9 nm was developed and used to reduce the uncertainties associated with the peroxy radical source based on water photolysis. A novel peroxy radical source based on OCIO was developed and employed to confirm the ambient humidity effect on the chain length of the radical detector. The humidity effect on the chain length can be reduced by heating the walls of the reactor and decreasing the residence time of the air sample in the reactor to avoid the possible interferences from thermolabile species.

Atmospheric ROx Radicals at an Urban Site: Comparison to a Simple Theoretical Model

Atmospheric RO x radicals (HO + HO 2 + RO + RO 2 ) were measured for 1 month in the summer of 1993 in Denver, CO. The results are correlated with solar UV fluxes and ozone mixing ratios monitored during the same period. The RO x radical measurements were also compared to predictions from a simple computer simulation. Significant free radical levels were observed during the early evening and nighttime and are believed to arise from the HO radical produced bythe reactions of ozone with ambient alkenes. Within the error bars of the measurements and approximations and assumptions in the calculations, the data appear to be in accord with the theoretical model.