Effect of relative humidity on hydrogen peroxide production in water droplets

Abstract

Mist is generated by ultrasonic cavitation of water (Fisher Biograde, pH 5.5-6.5) at room temperature (20 -25ºC) in open air with nearly constant temperature (22 -25 ºC) but varying relative humidity (24%-52%) over the course of many months. Water droplets in the mist are initially about 7 microns in diameter at about 50% relative humidity. They are collected, and the concentration of hydrogen peroxide (H 2 O 2 ) is measured using commercial peroxide test strips and by bromothymol blue oxidation. The quantification method is based on the Fenton chemistry of dye degradation to determine the oxidation capacity of water samples that have been treated by ultrasonication. It is found that the hydrogen peroxide concentration varies nearly linearly with relative humidity over the range studied, reaching a low of 2 parts per million (ppm) at 24% relative humidity and a high of 6 ppm at 52% relative humidity. Some possible public health implications concerning the transmission of respiratory viral infections are suggested for this threefold change in H 2 O 2 concentration with relative humidity.

Water–solid contact electrification causes hydrogen peroxide production from hydroxyl radical recombination in sprayed microdroplets

“…SI Appendix , Fig. S15 B shows that H 2 O 2 generation increased with increasing relative humidity, which is in good agreement with a previous literature report ( 35 ). To rule out in situ catalytic processes in the soil, we also investigated H 2 O 2 generation on O 2 plasma–activated and MTPMS-modified soil particles, respectively.…”

The Air–Water Interface of Water Microdroplets Formed by Ultrasonication or Condensation Does Not Produce H2O2

“…These findings could advance our understanding of environmental processes, such as the oxidation of S­(IV) species by H 2 O 2 in the presence or absence of Fe 2+ or Cu 2+ ions, leading to the acidification of clouds, dew, fog, etc. − Greener approaches for H 2 O 2 synthesis and the rational development of hydrogen peroxide-based automated room disinfection in hospitals, water treatment, oral care, etc., are other exciting avenues. The mechanism suggested for H 2 O 2 production in water microdroplets is based on the presence an an ultrahigh electric field at the air–water interface (∼10 7 V/cm), which drives the formation of •OH radicals from OH – ions; these •OH radicals combine to form H 2 O 2 . , Currently, there is no theoretical explanation available for this intriguing phenomenon. We note that probing the air–water interface of <1 nm dimensions is a daunting task and sometimes fraught with interpretational ambiguities and/or experimental artifacts. − …”

“…The mechanism suggested for H 2 O 2 production in water microdroplets is based on the presence an an ultrahigh electric field at the air−water interface (∼10 7 V/cm), which drives the formation of •OH radicals from OH − ions; these •OH radicals combine to form H 2 O 2 . 1,9 Currently, there is no theoretical explanation available for this intriguing phenomenon. We note that probing the air−water interface of <1 nm dimensions is a daunting task and sometimes fraught with interpretational ambiguities and/or experimental artifacts.…”

Ozone-Facilitated Formation of Uranyl Peroxide in Humid Conditions

“…The second major objective was to investigate the potential importance of atmospheric ozone in producing studtite from metaschoepite in high RH atmospheres. This objective was inspired by several recent studies that emphasize the formation of H 2 O 2 in droplets of water, ,, one of which recently argued that the formation of H 2 O 2 in microdroplets of water only occurs in the presence of ozone . Adding ozone produced from pure oxygen vastly enhanced the rate of conversion of metaschoepite to studtite.…”

“…Several recent reports demonstrate the formation of H 2 O 2 in microdroplets of water, the origin of which is hotly debated. − The role of atmospheric ozone in producing H 2 O 2 is relevant to the discussion, although one study argues that “the spontaneous generation of H 2 O 2 is universal on the surfaces of soil and atmospheric fine particles in a humid environment” and that H 2 O 2 originates from the hydroxyl groups on the solid surface . We hypothesize that the strong affinity of uranyl for peroxide together with the very low aqueous solubility of studtite under circumneutral pH conditions may favor the formation of studtite in some types of aqueous systems in the absence of added or radiolytically produced H 2 O 2 .…”