Pal Biswajit, Ariya Parisa A
Departments of Chemistry and Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec H3A 2K6, Canada.
Environ Sci Technol. 2004 Nov 1;38(21):5555-66. doi: 10.1021/es0494353.
Mercury is an environmentally volatile toxic fluid metal that is assumed to have a long atmospheric residence time and hence is subject to long-range transport. The speciation and chemical transformation of mercury in the atmosphere strongly influences its bioaccumulation potential in the human food chain as well as its global cycling. To investigate the oxidation of Hg0 by HO, the dominantdaytime atmospheric oxidant, we performed kinetic and product studies over the temperature range 283-353 K under near atmospheric pressure (100+/-0.13 kPa) in air and N2 diluents. Experiments were carried out by the relative rate method using five reference molecules and monitored by gas chromatography with mass spectroscopic detection (GC-MS). The HO were generated using UV photolysis of isopropyl nitrite at 300 < or = lambda < or = 400 nm in the presence of NO. The room-temperature rate constant was found to be (9.0+/-1.3) x 10(-14) cm3 molecule(-1) s(-1). The temperature dependence of the reaction can be expressed as a simple Arrhenius expression (in unit of 10(-14) cm3 molecule(-1) s(-1)) using ethane as the reference molecule: kHg + HO = 3.55 x 10(-14) exp((294+/-16)/T). The major reaction product, HgO, was identified in the gaseous form, as aerosols and as deposits on the container walls, using chemical ionization mass spectrometry (CI-MS), electron impact mass spectrometry (EI-MS), GC-MS, and cold vapor atomic fluorescence spectrometry (CVAFS). Experimental results reveal that ca. 6% of the reaction products were collected on a 0.2 microm filter as suspended aerosol, ca. 10% were in the gaseous form, and about 80% were deposited on the reaction vessel wall. The potential implications of our results in the understanding of tropospheric mercury transformation are herein discussed.
汞是一种在环境中易挥发的有毒液态金属，被认为在大气中的停留时间很长，因此会进行远距离传输。大气中汞的形态和化学转化强烈影响其在人类食物链中的生物累积潜力及其全球循环。为了研究大气中主要的日间氧化剂HO对Hg0的氧化作用，我们在接近大气压（100±0.13 kPa）的条件下，于283 - 353 K的温度范围内，在空气和氮气稀释剂中进行了动力学和产物研究。实验采用相对速率法，使用五种参考分子，并通过气相色谱 - 质谱检测（GC - MS）进行监测。HO是在存在NO的情况下，通过亚硝酸异丙酯在300≤λ≤400 nm的紫外光解产生的。发现室温速率常数为(9.0±1.3)×10⁻¹⁴ cm³·分子⁻¹·s⁻¹。使用乙烷作为参考分子，该反应的温度依赖性可以用一个简单的阿伦尼乌斯表达式表示（单位为10⁻¹⁴ cm³·分子⁻¹·s⁻¹）：kHg + HO = 3.55×10⁻¹⁴ exp((294±16)/T)。使用化学电离质谱（CI - MS）、电子轰击质谱（EI - MS）、GC - MS和冷蒸气原子荧光光谱法（CVAFS），确定主要反应产物HgO以气态、气溶胶形式以及容器壁上的沉积物形式存在。实验结果表明，约6%的反应产物以悬浮气溶胶的形式收集在0.2微米的滤膜上，约10%为气态，约80%沉积在反应容器壁上。本文讨论了我们的结果对理解对流层汞转化的潜在意义。
