Environ. Sci. Technol. 1993, 27, 2712-2718
Comparison of Collection Devices for Atmospheric Peroxides Claes de Serves’ and Howard B. Ross? Department of Meterology, Stockholm University, S-106 9 1 Stockholm, Sweden
Possible interferences affecting the diffusion scrubber and the scrubbing coil, two of the most widely used collection devices for real-time measurements of atmospheric peroxides, have been studied. Collection efficiencies for the coil were found to be >98 % for H2Oz and 49 % for peracetic acid; the diffusion scrubber is 21 % and 9.5% effective for these gases. Using MnO2 reactors for discrimination between H202 and organic peroxides showed that significant losses or complete destruction of organic peroxides occurred in the reactors. This will result in the underestimation of organic peroxides and a corresponding overestimation of H202 concentrations. Interferences by 0 3 were observed; adding 50 ppbv (parts per billion by volume) O3resulted in an increase in the H202 signal of 5 pptv (parts per trillion by volume) for the coil and 35 pptv for the diffusion scrubber. Severe sampling artifacts have been observed in the ambient air manifold indicating the need for proper gas-phase calibration techniques.
Introduction Due to the importance of atmospheric peroxides (H202 and organic peroxides; R02H) in the oxidation of SO2 and other compounds ( I , 2 ) , as well as its possible harmful effects on vegetation (3),there is a great interest in studying their atmospheric behavior. Different techniques for the analysis of gas-phase peroxides at low concentration (subppbv levels) have been developed. These include fluorometry (4, 51, chemiluminescence (6), colorimetry (7), HPLC for separation of the different peroxides (8,9), and laser absorption techniques (10). Laser absorption techniques allow for in situ measurements while the other analytical methods must collect the atmospheric peroxides for subsequent analysis. Various techniques and methods have been reported. Two of the most widely used collection techniques for real-time measurements of atmospheric peroxides are the glass scrubbing coil designed by Lazrus et al. ( 4 ) ,hereby referred to as “the coil”, and the diffusion scrubber, “the DS”, designed by Dasgupta et al. (11). When intercalibrations of these techniques were performed, systematic differences were observed (12, 13). For example, ambient air concentrations of HzO2 measured with the coil were generally 25% higher than the average value reported in the comparison, while the DS measured H202 levels generally 25 % lower (12). Since different analytical techniques, different methods for the collection of the peroxides, and different individual calibration sources were used in the intercalibration, it is not possible to identify the cause of the discrepancies. During field studies, where both the coil and the DS techniques were engaged, large differences in the measurements of organic peroxides were observed (14). The differentiation between HzO2 and organic peroxides from the total peroxide signal (H202 plus organic peroxides) +Present address: Sweden. 2712
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Environ. Sci. Technoi., Vol. 27, No. 13, 1993
was in both systems based on the selective destruction of H202. The concentration of H202 can then be determined by the difference between the total and the organic peroxide signals. The enzyme catalase was used in the coil system to consume H202. In the DS system, MnOz reactors, reported to consume H202 at a much faster rate than organic peroxides (15), were used. The analytical methods were otherwise based on the same chemistry and detection. The coil system measured organic peroxide levels up to about 30% of the total peroxide signal, while no organic peroxides were detected with the DS system using MnO2 reactors. We therefore concluded that either the DS membrane itself was selective for H202 or that the MnO2 reactor removed organic peroxides together with H202. Interferences by O3have been observed (16, 17) when collecting atmospheric peroxides in aqueous traps. Zika and Saltzman (I 7) concluded that O3and its decomposition products in aqueous solution, OH and Or,could cause large interferences by formation of artifact Ha02 when sampling atmospheric peroxides in fritted gas washing traps. Heikes (16) found a positive relationship between the loss of 0 3 and the generation of H202 when bubbling ozonized air (
