Oxidation Mechanisms of CF2Br2 and CH2Br2 Induced by Air Nonthermal Plasma

• Published in: Environmental science & technology 2013-01, Vol.47 (1), p.542-548
• Main Authors: Schiorlin, Milko, Marotta, Ester, Dal Molin, Marta, Paradisi, Cristina
• Format: Article
• Language: English
• Subjects: Air; Air Pollutants - chemistry; Applied sciences; Atmospheric pollution; Carbon Dioxide - chemistry; Carbon Monoxide - chemistry; Chlorofluorocarbons, Methane - chemistry; Exact sciences and technology; General processes of purification and dust removal; Hydrocarbons, Brominated - chemistry; Nitrous Oxide - chemistry; Oxidation-Reduction; Pollution; Prevention and purification methods; Spectroscopy, Fourier Transform Infrared; Sulfuric Acids - chemistry
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es303561n

Oxidation mechanisms in air nonthermal plasma (NTP) at room temperature and atmospheric pressure were investigated in a corona reactor energized by +dc, −dc, or +pulsed high voltage.. The two bromomethanes CF2Br2 and CH2Br2 were chosen as model organic pollutants because of their very different reactivities with OH radicals. Thus, they served as useful mechanistic probes: they respond differently to the presence of humidity in the air and give different products. By FT-IR analysis of the postdischarge gas the following products were detected and quantified: CO2 and CO in the case of CH2Br2, CO2 and F2CO in the case of CF2Br2. F2CO is a long-lived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however removed from the NTP processed gas by passage through a water scrubber resulting in hydrolysis to CO2 and HF. Other noncarbon containing products of the discharge were also monitored by FT-IR analysis, including HNO3 and N2O. Ozone, an important product of air NTP, was never detected in experiments with CF2Br2 and CH2Br2 because of the highly efficient ozone depleting cycles catalyzed by BrOx species formed from the bromomethanes. It is concluded that, regardless of the type of corona applied, CF2Br2 reacts in air NTP via a common intermediate, the CF2Br radical. The possible reactions leading to this radical are discussed, including, for −dc activation, charge exchange with O2 –, a species detected by APCI mass spectrometry.