Microprocessor-based air analyzer unit for sub parts per billion level measurements of hydrogen peroxide

A microprocessor (μP)-based sampler analyzer has been designed and used for measurements of atmospheric hydrogen peroxide (H ₂O ₂) concentration at levels of sub parts per billion (ppbV) and higher. With improved sampling and analysis techniques, the output data, with their linear variation over five orders of H ₂O ₂ concentration, allow accurate measurements in the presence of other oxidants like ozone and nitrogen oxides. The sampling (preconcentration) of atmospheric H ₂O ₂ is done in specially purified water using an impinger with an efficiency of ≈ 100%. The background level of H ₂O ₂ in this medium allows measurement of its atmospheric concentrations at the level of 0.1 ppbV with peak S/N value of ≈10. The analysis of the aqueous H ₂O ₂ involves the selective detection and measurement of the chemiluminescence (CL) output of its reaction with alkaline luminol. With on line precalibration, absolute measurement of the H ₂O ₂ concentration for each sampling event is obtained. Additional features include the facility to check the time dependence of the CL output profile and record of the daily minimum and maximum values for reference. The μP control of these sequential operations and subsequent data handling with an IBM compatible PC/XT allows long-time unattended operation for a selected number of cycles and subsequently provides the concentration profile plot on the printer. Ambient solar actinic irradiance is also recorded simultaneously for correlation studies of atmospheric chemical reactions.