Air Pollution- Particles in the Air
Air quality and particles
? Epidemiological (流行病学 ) evidence associates
atmospheric particles with diseases and mortality.
– Particles penetrate the lungs,blocking and irritating
air passages.
– Particles themselves could exert toxic effects,(toxic
substances present in the particles) [Polycyclic
Aromatic Hydrocarbons are examples of toxic
substances in aerosols.]
Particle deposition as a function of particle
diameters in various regions of the lung.
The larger a
particle is,the
more likely it is
deposited into
the upper part of
the respiratory
system.
The smaller a
particle is,the
deeper it can get
into the
respiratory
system.
Terms
? TSP,Total suspended particulate matter
? RSP,Respirable suspended particulate matter
? PM10,Particulate matter of less than 10 um;
equivalent to RSP.
? PM2.5,Particulate matter of less than 2.5 um
Air quality standards for particles
? US
– 15 ug/m3 (annual average) for PM 2.5 um
– 65 ug/m3 (daily average) for PM 2.5 um
? Hong Kong
– RSP,55 ug/m3 (annual),180 ug/m3 (daily)
– TSP,80 ug/m3 (annual),260 ug/m3 (daily)
Visibility and Aerosols
In a clear sky without any
particles,one can see as far
as 100-300 km.
Physics of visibility
? Visibility depends on the transmission of light through the
atmosphere and the ability of the eye to distinguish an
object because it contrasts with the background.
? A change in contrast with viewing distance occurs for both
dark,light and bright objects,
– With dark objects,the atmosphere introduces light,called "air
light",to the sight path,and the dark object appears lighter at
increasing distance until it bleeds into the background at the
horizon.
– With light objects,light is lost from the sight path with increasing
viewing distance,
In both cases,the result is the same—
The contrast between the object and the background
approaches zero when the light coming along the line
of sight from the object approaches the intensity of the
light from the background at the horizon,
When the eye can no longer distinguish the difference,
the contrast,between the object and the background,
the object can not be seen,and it is said to be beyond
the limit of visibility,
The mathematic expression for the extinction of contrast:
I =Io exp[-bx]
b,scattering coefficient or absorption coefficient,
x,distance
I,light intensity or contrast,
b = bsg + bsp + bag + bap
bsg and bsp are extinction coeff,caused by light scattering due
to gas and particles respectively.
bsp = bsdp + bsw are broken into contributions due to dry
particles and water associated with particles.
bag and bap are extinction coeff,caused by light absorption
due to gas and particles respectively.
Visibility reduction due to particles is size-dependent
Particle
Scattering
and
absorption
cross-section
per unit
volume
Particles of 0.1-1.0 um size are
efficient light-scattering centers.
Fine aerosol particles are a major contributor to
visibility impairment
(Blue Ridge Mountain area in the U.S.)
Category % bext
Scattering due to gases 5.0
Scattering due to dry particles 49.1
Scattering due to particle bound water 43.1
Absorption due to gases 0.3
Absorption due to particles 2.5
Measurement of visibility
? Human observations
? Optical measurements
ext
v bL
91.3
? Measured by a integrating
nephelometer
Visual range
Study questions
1,How do particles cause adverse effect on
human health?
2,How do particles affect visibility?
Air quality and particles
? Epidemiological (流行病学 ) evidence associates
atmospheric particles with diseases and mortality.
– Particles penetrate the lungs,blocking and irritating
air passages.
– Particles themselves could exert toxic effects,(toxic
substances present in the particles) [Polycyclic
Aromatic Hydrocarbons are examples of toxic
substances in aerosols.]
Particle deposition as a function of particle
diameters in various regions of the lung.
The larger a
particle is,the
more likely it is
deposited into
the upper part of
the respiratory
system.
The smaller a
particle is,the
deeper it can get
into the
respiratory
system.
Terms
? TSP,Total suspended particulate matter
? RSP,Respirable suspended particulate matter
? PM10,Particulate matter of less than 10 um;
equivalent to RSP.
? PM2.5,Particulate matter of less than 2.5 um
Air quality standards for particles
? US
– 15 ug/m3 (annual average) for PM 2.5 um
– 65 ug/m3 (daily average) for PM 2.5 um
? Hong Kong
– RSP,55 ug/m3 (annual),180 ug/m3 (daily)
– TSP,80 ug/m3 (annual),260 ug/m3 (daily)
Visibility and Aerosols
In a clear sky without any
particles,one can see as far
as 100-300 km.
Physics of visibility
? Visibility depends on the transmission of light through the
atmosphere and the ability of the eye to distinguish an
object because it contrasts with the background.
? A change in contrast with viewing distance occurs for both
dark,light and bright objects,
– With dark objects,the atmosphere introduces light,called "air
light",to the sight path,and the dark object appears lighter at
increasing distance until it bleeds into the background at the
horizon.
– With light objects,light is lost from the sight path with increasing
viewing distance,
In both cases,the result is the same—
The contrast between the object and the background
approaches zero when the light coming along the line
of sight from the object approaches the intensity of the
light from the background at the horizon,
When the eye can no longer distinguish the difference,
the contrast,between the object and the background,
the object can not be seen,and it is said to be beyond
the limit of visibility,
The mathematic expression for the extinction of contrast:
I =Io exp[-bx]
b,scattering coefficient or absorption coefficient,
x,distance
I,light intensity or contrast,
b = bsg + bsp + bag + bap
bsg and bsp are extinction coeff,caused by light scattering due
to gas and particles respectively.
bsp = bsdp + bsw are broken into contributions due to dry
particles and water associated with particles.
bag and bap are extinction coeff,caused by light absorption
due to gas and particles respectively.
Visibility reduction due to particles is size-dependent
Particle
Scattering
and
absorption
cross-section
per unit
volume
Particles of 0.1-1.0 um size are
efficient light-scattering centers.
Fine aerosol particles are a major contributor to
visibility impairment
(Blue Ridge Mountain area in the U.S.)
Category % bext
Scattering due to gases 5.0
Scattering due to dry particles 49.1
Scattering due to particle bound water 43.1
Absorption due to gases 0.3
Absorption due to particles 2.5
Measurement of visibility
? Human observations
? Optical measurements
ext
v bL
91.3
? Measured by a integrating
nephelometer
Visual range
Study questions
1,How do particles cause adverse effect on
human health?
2,How do particles affect visibility?
