Australian Science Illustrated — Issue 54 2017

TECHNOLOGY SMOG

44 | SCIENCE ILLUSTRATED

on a cold winter day is now -25-35 degrees

C. That's actually pretty warm.

One of the systems affected by a warmer

Arctic is the polar jet stream: a tremendous

air current located about 60 degrees north of

the Equator. The stream winds around the

entire world about 10 km above sea level.

The jet stream contributes to defining the

boundary between cold and warm climates

• a difference which also makes up the jet
  stream’s "engine". When the Arctic is heated

fast, the temperature difference between

the polar regions and the subtropics is

reduced, causing the jet stream to lose

momentum, so the twists of the stream tend

to stop instead of continuing to flow west to

east. So the same air mass remains in the

same place for a long period of time, and can

trap smog over a city for days.

WAR AGAINST SMOG PAYS OFF

China is entering its fourth year of the war

against smog, and the struggle for clean air

is already beginning to pay off. Although

Beijing’s air quality remains alarmingly poor

on some days, the number of days with

acceptable air quality in 2016 was 198. In the

same year, the level of hazardous PM2.5

pollution had fallen by about 10% as

compared to the level in 2015.

The improvements have been made thanks

to large-scale efforts by the authorities, which

have established strict rules for the emissions

INDUSTRY

Smoke from factories and heavy industry can cause

a dense cloud of smog over the big cities of China,

forcing the citizens to stay indoors several days a year.

In January 2017, major parts of

Eastern China were veiled in dense

smog for days, as recorded by NASA’s

Suomi NPP satellite. The situation

occurs several times every winter,

when high pressure stalls

atmospheric circulation, capturing

the pollution in a "gas chamber" 10-

50 m above the ground. The

authorities use the satellite images

to make citizens stay indoors, and

they must often close schools and

other public spaces, until the

weather changes.

High pressure:

smog for days

Even from the satellite’s

orbit 824 km above Earth,

the smog over Eastern

China is evident.

Satellite warns people of smog

Eastern China is surrounded by mountains, making the region vulnerable to lengthy periods of

toxic fog. Satellites help the authorities issue warnings, so people can avoid the worst smog.

SMOG

SUOMI NPPSATELLITE

Now

SMOG REDUCTION:
0 %

JEFF SCHMALTZ, LANCE/EOSDIS RAPID RESPONSE/NASA & NOAA