In this week, the worst round of air pollution
hit China. Beijing became the biggest victim, under a cloud of smog since last Saturday.
Murky haze raised the number of patients in respiratory and skin disease; children
are kept from doing practice outside; 58 factories were suspended work and 30%
of government vehicles off the road. Based on the US Embassy’s record, Levels
of PM 2.5 particles (airborne particulate matter with a diameter of 2.5 microns
or less, which can cause health problems when inhaled) in Beijing had reached
to 500 in Tuesday which is beyond the index level. (shown below)
In fact, it’s not an occurrence for Chinese
people. They have been long term lived in a terrible environment. Based on the
Index at Yale University, China’s environmental performance ranks 116th
overall, and 128th on its air quality. In the top 10 cities with worst
air quality, 7 are from China. This is an embarrassing score for China who is
the 2nd largest economic entity in the world. What happened to this
country?
From the environment center, there are 3
reasons caused dust haze:
1.
The direct
reason is high emission of pollution and dust. Mainly from 3 main pathways:
coal mining, industries and vehicles.
2.
Construction’s
block and friction reduced the movement of air and reduce the speed of little particles
diffusion.
3.
The location
of Beijing is surrounded by hills, further retarded the airflow in the city.
Plus huge humidity of the section between winter and spring. Finally form this
pollution event.
For these reasons, besides the 2nd
reason is directly related to construction, the first reason is more or less
related to construction, or say, construction chain including industrial phase
and operation phase. Actually, in the production of construction materials,
lots of pollutions are emitted including imperfect combustion carbon particles,
heavy medal particles and other chemical gases such as CO, SO2, NOX
and toxic organic gas such as Dioxin, ect. Also in the operation phase, coal
mine are the major heat and electrical resources in most of the cities in China
which makes the control of the energy consumption in buildings a big issue.
China is struggling with how to reduce dust
emission in construction right now. It seems too far away to talk about how to
reduce carbon footprint because in all, carbon dioxide widely exists in the
nature and seems not to toxic compare to these materials above. However, from
my point of view, the solution of reduces construction dust and carbon
footprint is can be the same: reduce usage of fossil energy and increase efficiency
on them. Although it is not a new story and needs really long (maybe hundreds
years) effort on.
Back to the of Beijing’s haze issue,
construction may be the major reason but not the only one. In short term, this
situation may not have a big change. But by analyzing the reasons, I learned
something from it. Construction as a heavy cement structure in the city not
only cause heat island effect, but also retarded the air movement. Dust will
then sink down to the “low level” area. Therefore, as a city planner planning a
city, try not committing a city center which tall buildings and skyscrapers are
gathered in the same area. For constructors, try to design low friction surface
so that air around it can freely move away.
At the last, I would like to raise a feasibility
discussion, is it possible to build up an air filter system for a whole city
with little energy? I am thinking about using convection. Diagraph showing
below.
These lines underground are ventilation system. During
the daytime, sun will heat up one side of the buildings and the other side is become
cooler. If we can build up underground ventilation system in the city, when
cooler air move to the hotter area it will suck the nearby dust goes
underground. As the sun goes from one side to another, the air will be moved back
and force. The dust will move with air. If then we install a filter in the
middle, it will finally collect the dust.
No comments:
Post a Comment