Mist can­non used to fight heavy smog

China Daily (Hong Kong) - - TOP NEWS - By ZHENG JINRAN zhengjin­ran@chi­nadaily.com.cn

Heavy smog that has been cov­er­ing many cities in northern China has caused some au­thor­i­ties to bring out pollution-fight­ing ar­tillery.

The mist can­non, which is not well-known but gain­ing pop­u­lar­ity, is a large ma­chine mounted on a truck that sprays wa­ter mist.

They were ini­tially used at con­struc­tion sites and mines to re­duce dust. But en­gi­neers have im­proved the ma­chines to make them re­lease tinier droplets of mist for com­bat­ing fine air­borne par­ti­cles, said Xu Yuexin, an en­gi­neer with Bei­jing Cap­i­tal Group Boom-sound En­vi­ron­ment Science & Tech­nol­ogy Co Ltd, which pro­vides the mist can­non ser­vice in parts of the cap­i­tal.

“The truck works by neb­u­liz­ing wa­ter into tiny par­ti­cles, with di­am­e­ters in mi­crons, the same as PM2.5 and PM10, and spray­ing them into the air, and then they could com­bine with the dust and fine par­ti­cles to fall to the ground,” Xu said.

Ex­perts have found they’re ef­fec­tive, but have their lim­its. They are, of­fi­cials said, only one of the mea­sures be­ing taken. Tough re­stric­tions on emis­sions is still the best way to con­trol air pollution for the longer term.

Bei­jing res­i­dents woke up to thick smog over the week­end, with the air pollution read­ings of 21 mon­i­tor­ing sta­tions climb­ing to the most haz­ardous level in the early hours of Sun­day. The vis­i­bil­ity was re­duced to within 500 me­ters in some ar­eas.

The smog, which also cov­ered vast ar­eas of the coun­try’s north, was mainly a prod­uct of wind­less weather that was un­able to dis­perse pol­lu­tants, ac­cord­ing to en­vi­ron­men­tal au­thor­i­ties in the af­fected ar­eas.

The cap­i­tal is­sued its sec­ond-high­est warn­ing against air pollution, an or­ange alert, on Thurs­day, one day be­fore smog cov­ered the city. Un­der an or­ange alert, the cap­i­tal takes com­pre­hen­sive mea­sures to con­trol the emis­sions from com­pa­nies, ve­hi­cles and con­struc­tion sites.

Im­ple­men­ta­tion of re­stric­tions un­der the alerts has been strength­ened, of­fi­cials said. In Bei­jing on Sun­day, the alert prompted in­spec­tors to mon­i­tor 533 com­pa­nies and con­struc­tion sites, and check over 57,800 ve­hi­cles, the mu­nic­i­pal en­vi­ron­men­tal bu­reau said.

The mist can­non trucks are be­ing used to spray in the morn­ings, and do so more fre­quently, some three to five times, dur­ing smoggy days.

Au­thor­i­ties also spray spe­cial chem­i­cals on the roads through reg­u­lar wa­ter­ing ve­hi­cles once a week. The spray ab­sorbs and con­sol­i­dates the dust and pol­lu­tants from ve­hi­cle ex­haust, Xu said.

The com­bi­na­tion of the mist can­non and the chemi- cals “have been de­ter­mined ef­fec­tive in re­duc­ing the fine par­ti­cles”, Xu said.

Ac­cord­ing to tests con­ducted by re­searchers with the China National En­vi­ron­men­tal Mon­i­tor­ing Cen­ter, the mist can­non and the chem­i­cals can to­gether “cut the PM10 by 20 per­cent, PM2.5 by 5 per­cent and ni­tro­gen ox­ides by 10 per­cent”, ac­cord­ing to Xu.

There are two trucks cov­er­ing 35 streets in the cap­i­tal’s Chaoyang dis­trict, mainly around the Olympic venues and re­gions where em­bassies are con­cen­trated, be­cause of the high pop­u­la­tion den­si­ties and fre­quency of events. The trucks started op­er­at­ing in Oc­to­ber and plans call for them to con­tinue to April 2017.

The gov­ern­ment should pay more at­ten­tion to im­ple­ment­ing mea­sures to cut the emis­sions at their source, said Shi Guo­liang, as­so­ciate pro­fes­sor of en­vi­ron­men­tal sciences at Nankai Univer­sity in Tian­jin.

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