Both Sides Now

Detection of Sulfur Dioxide by Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS)

Sulfur dioxide (SO2) is an important precursor for the formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO2 with a minimum limit of detection of 0.75 ppbv (3-σ) using the spectral range 305.5–312 nm and an averaging time of 5 min. The instrument consists of high-reflectivity mirrors (0.9985 at 310 nm) and a deep UV light source (Light Emitting Diode). The effective absorption path length of the instrument is 610 m with a 0.966 m base length. Published reference absorption cross sections were used to fit and retrieve the SO2 concentrations and were compared to fluorescence standard measurements for SO2. The comparison was well correlated, R2 = 0.9998 with a correlation slope of 1.04. Interferences for fluorescence measurements were tested and the BBCEAS showed no interference, while ambient measurements responded similarly to standard measurement techniques.

H2O2 formation from photocatalytic processes at the ZnO/water interface

The paper focuses on the production of H2O2 by photocatalysis over ZnO in an aerated aqueous phase. The presence of different reductants that increase the H2O2 production in the aqueous phase is analysed; particular attention is paid to nitrite, which has been shown to be the reductant that produces the most significant increments in the H2O2 production. The photocatalytic anodic decomposition of ZnO in the presence of the different reductants is also investigated. From the results obtained, the relevance of the ZnO photocatalysis in the formation of environmental hydrogen peroxide is estimated.

Acid Deposition: Unraveling a Regional Phenomenon

Because sources of sulfur and nitrogen oxides distributed broadly across eastern North America have greatly overlapping zones of influence, it is difficult to determine detailed relations between emissions and the resulting acid deposition. Although substantial progress has been made in the past decade in understanding the pertinent atmospheric processes and in describing them in numerical models, because of the complexities of these processes and the wide range of the time and space scales involved, credible source-receptor relations for regional-scale acid deposition are not yet at hand. Consequently, near-term strategies for reducing acid deposition should be based on considerations other than detailed atmospheric source-receptor relations, but with confidence that regional deposition will be reduced equivalently to any reduction in regional emissions.