环境污染英语课件

sandstromWhatis"sandstorm"?

Sandstormisameteorologicalphenomenoncommonlyfoundinaridandsemi-aridregions.Itisresultedfromconvectioncurrentscreatedbyintensiveheatingoftheground.Thesecurrentscancreatewindupto120km/handappearasasolidwallofdustasmuchas1,525mhighwhichblowoveralongdistance.

Sandstormisakindofclimatichazard.Itoccurswhenstrongwindraisesandcarriesalongcloudsofsandordustwhichissodensethatitobscurethesunandreducevisibilitytolessthan1km.Sandstormusuallyoccursindesertsorareasneartoaridandsemi-aridregions.ItwasfoundinareaslikeSaharaDesertinNorthAfrica,CentralAustralia,SouthwestofUSA,CentralAsiaandNorthwestChina.

Conditionsfortheformationofsandstorms

Aspecialistinmeteorologypointedoutthatsandstormswereformedunderthreeconditions:strongwind,richsourceofsandandunstableairconditions.Thethreeconditionscanbearesultofnaturalcauses.However,forthesecondcondition,thesupplyofsandismoreofaresultofdesertificationcausedbyhumanactivities.

Duststorms

are

largely

created

by

man

himself.

On

the

one

hand,

too

much

air

pollution

causes

a

greenhouse

effect,

which,

in

turn,

leads

to

global

wanning

in

climate.

This

results

in

wet

places

on

the

earth

even

wetter

and

dry

places

even

drier.

On

the

other

hand,

over

grazing,

poor

fanning,

tree

cutting,

strip

mining

all

leave

theland

unprotected.

When

the

wind

blows,

it

blows

away

topsoil

and

loose

soil.

Thehazards,anditsharmsandstormwaygenerallycanbeclassifiedint