京津冀连续两天受“臭氧污染”侵扰
<p>根据环保部空气质量预测预报，18日至19日，京津冀及周边地区会出现一次污染过程，北京、天津、河北中南部部分城市空气质量可能达到中度污染，短时可至重度污染，首要污染物为臭氧。</p><p><span word="Beijing">Beijing</span>, <span word="Tianjin">Tianjin</span>, <span word="and">and</span> <span word="parts">parts</span> <span word="of">of</span> <span word="Hebei">Hebei</span> <span word="Province">Province</span> <span word="will">will</span> <span word="suffer">suffer</span> <span word="from">from</span> <span word="moderate">moderate</span> <span word="to">to</span> <span word="heavy">heavy</span> <span word="levels">levels</span> <span word="of">of</span> <span word="air">air</span> <span word="pollution">pollution</span> <span word="on">on</span> <span word="May">May</span> 18 <span word="and">and</span> 19, <span word="with">with</span> <span word="O">O</span>3 <span word="as">as</span> <span word="the">the</span> <span word="primary">primary</span> <span word="pollutant">pollutant</span>, <span word="the">the</span> <span word="Ministry">Ministry</span> <span word="of">of</span> <span word="Environmental">Environmental</span> <span word="Protection">Protection</span> (<span word="MEP">MEP</span>) <span word="said">said</span> <span word="Thursday">Thursday</span>.</p><p>环保部18日表示，18日至19日，北京、天津及河北部分地区空气质量可能达到中度污染，首要污染物为臭氧。</p><p>臭氧（<span word="ozone">ozone</span>）是地球大气中一种微量气体，大气中90%以上的臭氧存在于大气层的上部或平流层（<span word="stratosphere">stratosphere</span>），离地面有10～50千米，可以吸收太阳释放出来的绝大部分紫外线（<span word="ultra">ultra</span>-<span word="violet">violet</span> <span word="ray">ray</span>），使动植物免遭这种射线的危害。但是，近地面大气中的臭氧，主要由人类活动产生的污染物经过一系列复杂的光化学反应（<span word="photochemical">photochemical</span> <span word="reaction">reaction</span>）而产生，一旦超标，对环境以及人体健康的危害都很大。</p><p>地面臭氧（<span word="ground">ground</span>-<span word="level">level</span> <span word="ozone">ozone</span>）的形成主要有两大要素，一是由发电厂、燃煤锅炉、涂料油漆和机动车尾气排放出的“氮氧化物”（<span word="nitrogen">nitrogen</span> <span word="oxides">oxides</span>）和“挥发性有机物”（<span word="volatile">volatile</span> <span word="organic">organic</span> <span word="compounds">compounds</span>）；二是高温和光照。每当夏季来临，气温升高（<span word="rising">rising</span> <span word="temperature">temperature</span>），光照增强，加之污染物排放，臭氧极易发生超标现象。</p>
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