摘要:

Heterogeneous reaction of sulfur dioxide (SO2) on mineral dust is known to be an important pathway for SO2 removal mainly resulting in sulfate formation in the atmosphere, and its kinetic and mechanism can be significantly influenced by the presence of trace gases, such as, O3, NO2 and H2O2. However, little is known about the role of carbonyl compounds, such as formaldehyde (HCHO), that plays in this reaction. In this study, we investigated the heterogeneous reaction of SO2 on mineral dust, in this case, α-Al2O3 and SiO2 particles, in the presence of HCHO at different RHs using a flow reactor coupled with transmission-Fourier transform infrared (T-FTIR). Infrared spectra show that hydroxymethanesulfonate (HMS) can be formed through the interaction of HCHO with adsorbed SO2 on mineral dust even under dry conditions. HCHO plays a double-edged role in the heterogeneous reactions of SO2 at different RHs. The presence of HCHO inhibits the adsorption of SO2 on particles under dry conditions by competing with surface active sites, while it facilitates the amount of SO2 uptake by particles (N) at high RH by providing addition pathway for SO2 conversion. This enhancement also significantly shortens the discrepancy in different heterogeneous reactivity of particles towards SO2. The N value for α-Al2O3 particles is 5.2 times larger than SiO2 particles for particles exposed to SO2 alone, but this increase factor drops to 1.6 in the presence of HCHO at 80% RH. These findings deepen the understanding of SO2 heterogeneous chemistry in the atmosphere and how it is affected by the coexistence of other trace gases.

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