Environment Research Institute, Shandong University, Qingdao 266237, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong 999077, China.
Division of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong 999077, China.
J Environ Sci (China). 2021 Aug;106:124-135. doi: 10.1016/j.jes.2021.01.018. Epub 2021 Jan 31.
Heterogeneous reactions of NO on different surfaces play an important role in atmospheric NO removal and HONO formation, having profound impacts on photochemistry in polluted urban areas. Previous studies have suggested that the NO uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime. However, the uptake behavior of NO varies with different surfaces, and different uptake coefficients were used or derived in different studies. To obtain a more holistic picture of heterogeneous NO uptake on different surfaces, a series of laboratory experiments using different flow tube reactors was conducted, and the NO uptake coefficients (γ) were determined on inorganic particles, sea water and urban grime. The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions, with the measured γ varied from <10 to 3.2 × 10 under different humidity. A photo-enhanced uptake of NO on urban grime was observed, with the obvious formation of HONO and NO from the heterogeneous reaction. The photo-enhanced γ was measured to be 1.9 × 10 at 5% relative humidity (RH) and 5.8 × 10 at 70% RH on urban grime, showing a positive RH dependence for both NO uptake and HONO formation. The results demonstrate an important role of urban grime in the daytime NO-to-HONO conversion, and could be helpful to explain the unknown daytime HONO source in the polluted urban area.
不同表面上的 NO 异相反应在大气 NO 去除和 HONO 形成中起着重要作用，对污染城市地区的光化学有深远影响。先前的研究表明，地面或气溶胶表面上的 NO 吸收可能是白天 HONO 升高的主要来源。然而，NO 的吸收行为因不同的表面而异，不同的研究中使用或推导了不同的吸收系数。为了更全面地了解不同表面上的异相 NO 吸收，使用不同的流动管反应器进行了一系列实验室实验，并确定了无机颗粒、海水和城市污垢表面上的 NO 吸收系数（γ）。结果表明，这些表面在黑暗条件下的异相反应通常较弱，在不同湿度下测量的γ值从<10 到 3.2×10 不等。在城市污垢上观察到了 NO 的光增强吸收，通过异相反应明显形成了 HONO 和 NO。在 5%相对湿度（RH）和 70%RH 下，城市污垢上的光增强 γ 值分别为 1.9×10 和 5.8×10，NO 吸收和 HONO 形成均表现出对 RH 的正依赖性。结果表明，城市污垢在白天的 NO 向 HONO 转化中起着重要作用，有助于解释污染城市地区未知的白天 HONO 来源。
