Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University , Kowloon, Hong Kong 999077, China.
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences , Beijing 100085, China.
Environ Sci Technol. 2017 Apr 4;51(7):3767-3775. doi: 10.1021/acs.est.6b05724. Epub 2017 Mar 14.
Nitrous acid (HONO) is an important source of hydroxyl radical (OH) that determines the fate of many chemically active and climate relevant trace gases. However, the sources and the formation mechanisms of HONO remain poorly understood. In this study, the effect of SO on the heterogeneous reactions of NO on MgO as a mineral dust surrogate was investigated. The reactivity of MgO to NO is weak, while coexisting SO can increase the uptake coefficients of NO on MgO by 2-3 orders of magnitude. The uptake coefficients of NO on SO-aged MgO are independent of NO concentrations in the range of 20-160 ppbv and relative humidity (0-70%RH). The reaction mechanism was demonstrated to be a redox reaction between NO and surface sulfite. In the presence of SO, NO was reduced to nitrite under dry conditions, which could be further converted to gas-phase HONO in humid conditions. These results suggest that the reductive effect of SO on the heterogeneous conversion of NO to HONO may have a significant contribution to the unknown sources of HONO observed in polluted areas (for example, in China).
亚硝酸（HONO）是决定许多化学活性和气候相关痕量气体命运的羟基自由基（OH）的重要来源。然而，HONO 的来源和形成机制仍知之甚少。在这项研究中，研究了 SO 对 MgO 作为矿物尘替代物上 NO 异相反应的影响。MgO 与 NO 的反应性较弱，而共存的 SO 可以将 NO 在 MgO 上的吸收系数增加 2-3 个数量级。NO 在 SO 老化的 MgO 上的吸收系数与 20-160 ppbv 和相对湿度（0-70%RH）范围内的 NO 浓度无关。反应机理被证明是 NO 和表面亚硫酸盐之间的氧化还原反应。在 SO 的存在下，NO 在干燥条件下被还原为亚硝酸盐，在潮湿条件下可以进一步转化为气相 HONO。这些结果表明，SO 对 NO 向 HONO 异相转化的还原作用可能对污染地区（例如中国）观测到的 HONO 未知来源有重要贡献。
