Pure smoke in the chim­ney

About half of the world’s coal burn­ing takes place in China, but the huge coun­try also has one of the most am­bi­tious schemes for con­vert­ing its en­ergy gen­er­a­tion into clean and green en­ergy.

Science Illustrated - - TECHNOLOGY -

un­fil­tered into the blood stream, which will carry them to all body tis­sue.

In 1991, Amer­i­can sci­en­tists, who had ob­served 8,111 in­di­vid­u­als for 17 years, showed that early deaths were not evenly dis­trib­uted among the pop­u­la­tions of eight cities. There were more deaths in ar­eas with con­sid­er­able air par­ti­cle pol­lu­tion. In 1999, sci­en­tists were able to make another ground­break­ing con­clu­sion: cities which had done a lot to com­bat pol­lu­tion in the pre­vi­ous eight years had re­duced the num­ber of early deaths con­sid­er­ably.

The pos­i­tive mes­sage: it is worth­while do­ing some­thing – even in the short term.

In re­cent decades, sci­en­tists have also re­alised that the tinier the smog par­ti­cles, the more haz­ardous they are. Tiny par­ti­cles are more likely to pro­duce re­ac­tive and highly ox­i­dis­ing per­ox­ides. Ox­i­da­tion is a harm­ful process for body cells, speed­ing up age­ing and pos­si­bly con­vert­ing healthy cells into can­cer cells. In the cells, per­ox­ides could harm other chem­i­cal com­pounds by ox­i­dis­ing them, so they can no longer func­tion as in­tended, such as DNA and other cel­lu­lar struc­tures.

So, to­day ef­forts are fo­cused on mea­sur­ing and min­i­miz­ing the num­ber of harm­ful par­ti­cles sized “PM2.5”. PM is short for par­tic­u­late mat­ter such as fine dust par­ti­cles, and 2.5 refers to the di­am­e­ter of the par­ti­cles, which av­er­age 2.5 mi­crome­tres

( m). A 2.5 m par­ti­cle is about 30 times smaller than the thick­ness of a hu­man hair.

The par­ti­cles form in sev­eral ways such as by com­bus­tion, ox­i­da­tion of nitro­gen and sul­phur com­pounds, and other chem­i­cal re­ac­tions in the at­mos­phere. If you are sur­rounded by air with a high con­tent of PM2.5 par­ti­cles, you suf­fer a markedly greater risk of de­vel­op­ing lung dis­eases such as asthma, bron­chi­tis, and lung can­cer. So, the WHO has es­tab­lished a thresh­old value of 10 mi­cro­grammes of the par­ti­cles per cu­bic me­tre of air. Sadly, this thresh­old is of­ten crossed by many cities of the world, in­clud­ing Euro­pean ones, but the sit­u­a­tion is the worst in China. Even when au­thor­i­ties have been forced to es­tab­lish a higher thresh­old - 35 mi­cro­grammes per cu­bic me­tre - the cities are sim­ply un­able to com­ply.

Par­ti­cles also ex­ist which are tinier than PM2.5, whose sizes are mea­sured on a nanoscale. Doc­tors are not yet sure, but the par­ti­cles might cause other prob­lem. Mouse stud­ies show that par­ti­cles of less than 200 nanome­tres or 0.2 m can en­ter di­rectly from the res­pi­ra­tory sys­tem to the body, where they travel along nerve cells, end­ing up in the brain, where they cause in­fec­tion and

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