<p>Large clouds of smog are not uncommon in northern China and the situation typically grows worse during the winter when energy use increases. ;</p>
<p>At least 23 cities are currently under red alert, and 700 companies in Beijing have stopped production. The smog is so bad in some areas that planes can&rsquo;t even land. ;</p>
<p>Hospitals are overwhelmed with patients complaining of asthma and other respiratory conditions. ;</p>
<p>&ldquo;The smog has serious repercussions on the lungs and respiratory system,&rdquo; explains Beijing high school student Li Jingren. &ldquo;It also influences the health of future generations, so under a red alert, it is safer to stay at home rather than go to school.&rdquo; ;</p>
<p>Beijing is one of the most polluted cities in the world &ndash; a problem that has been blamed on China&rsquo;s reliance on coal as well as emissions from old cars. Greenpeace climate campaigner Dong Liansai says emissions from nearby factories caused the current smog episode. ;</p>
<p>Experts are tracking the miasma&#8217;s movement as well as the levels of potentially hazardous particles &ndash; called PM2.5 &ndash; in the air. ;</p>
<p>&ldquo;Off-the-charts air pollution chokes many places in the #Hebei province, w/ PM2.5 levels exceeding 1,000 in its capital city of #Shijiazhuang,&rdquo; tweeted the <em>People&rsquo;s Daily. ;</em></p>
<p>The alert was announced last Friday and is expected to end Wednesday night.</p>
<p> ;</p>
<p> ;</p>