{"id":3078,"date":"2020-05-17T07:04:06","date_gmt":"2020-05-17T03:34:06","guid":{"rendered":"https:\/\/www.sru.ac.ir\/en\/?p=3078"},"modified":"2020-05-17T07:04:47","modified_gmt":"2020-05-17T03:34:47","slug":"cloud-at-cern-reveals-a-new-mechanism-behind-urban-smog","status":"publish","type":"post","link":"https:\/\/www.sru.ac.ir\/en\/cloud-at-cern-reveals-a-new-mechanism-behind-urban-smog\/","title":{"rendered":"CLOUD at CERN reveals a new mechanism behind urban smog"},"content":{"rendered":"

The CLOUD collaboration has revealed a new mechanism that drives winter smog episodes in cities. The results,\u00a0published yesterday\u00a0in the journal\u00a0Nature<\/em><\/a>, could help inform policies for reducing urban particle pollution, which ranks fifth in the risk factors for mortality worldwide.<\/p>\n

Winter urban smog episodes occur when new particles form in polluted air trapped below a temperature inversion. The warm air above the inversion inhibits convection, causing pollution to build up near the ground. However, how additional aerosol particles manage to form and grow in this highly polluted air has been a mystery until now, because\u00a0they should be rapidly lost through scavenging by pre-existing aerosols. A new result from CLOUD could explain the mystery.<\/p>\n

The CLOUD experiment (Cosmics Leaving Outdoor Droplets) at CERN involves a special cloud chamber capable of mimicking all the diverse aspects of Earth\u2019s atmosphere, with precise control of the conditions and extremely low contaminants. Data from sampling instruments attached to the chamber allow a comprehensive understanding of the formation of aerosol particles and their effect on clouds and climate. Ions from cosmic rays can also influence aerosol formation, and their contributions are studied by varying the intensity of a pion beam from CERN\u2019s Proton Synchrotron, which passes through the chamber.<\/p>\n

In their new study, CLOUD scientists simulated polluted urban conditions in the chamber and investigated the role of ammonia and nitric acid at\u00a0atmospheric concentrations. Global emissions of ammonia are dominated by farming. In cities, however, the presence of both ammonia and nitric acid \u2013 which derives from nitrogen oxides (NOx) – is largely due to vehicles.<\/p>\n

“Ammonia and nitric acid were previously thought to play a passive role in particle formation, simply exchanging with ammonium nitrate in the particles\u201d, says Jasper Kirkby, head of the CLOUD experiment.<\/p>\n

However, the new CLOUD study showed that small inhomogeneities in the concentrations of ammonia and nitric acid – which only persist for a few minutes – can lead to particle growth rates up to more than 100 times faster than previously seen, but only in short spurts that have escaped detection so far. These ultrafast growth rates are sufficient to rapidly transform the newly formed particles\u00a0to larger size, where they are\u00a0less prone to being lost through scavenging by pre-existing particles. The end result is a dense smog episode with a high number of particles.<\/p>\n

\u201cAlthough the emission of nitrogen oxides is regulated, ammonia\u00a0emissions are not and may even be increasing with the latest catalytic converters used in gasoline and diesel vehicles. Our study shows\u00a0that regulating ammonia emissions from vehicles could contribute to reducing urban smog,\u201d concludes Jasper Kirkby.<\/p>\n

See more<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

The CLOUD collaboration has revealed a new mechanism that drives winter smog episodes in cities<\/p>\n","protected":false},"author":9,"featured_media":3079,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[32,8],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/posts\/3078"}],"collection":[{"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/users\/9"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/comments?post=3078"}],"version-history":[{"count":1,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/posts\/3078\/revisions"}],"predecessor-version":[{"id":3080,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/posts\/3078\/revisions\/3080"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/media\/3079"}],"wp:attachment":[{"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/media?parent=3078"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/categories?post=3078"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sru.ac.ir\/en\/wp-json\/wp\/v2\/tags?post=3078"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}