A&WMA International Specialty Conference: Leapfrogging Opportunities
for Air Quality Improvement
Relationship of aerosol size
distribution and visibility in a sea fog
L. F. Sheng1, W. F. Liang2, W. J. Qu1, K. Luo1
1 College of Physical and Environmental Oceanography,
Ocean University of China,
2 Qingdao Meteorological Bureau
May 11, 2010, xian
Contents
•
•
•
•
Research background
Data source
Formation and evolution of the fog
Relationship of atmospheric aerosol
concentration and horizontal visibility
• Size distribution of the atmospheric aerosol
• summary
Research background
Sea fog (marine fog) occurs frequently in china coast areas.
Foggy month shifts northward with time.
fog days in Qingdao is about 51.5d on 30-year average, and the
maximum is in July, it’s about 10.5d(Jiang et al. 2008)
Qingdao
Jun.
Jul.
May
Apr.
Topography map of qingdao area
Feb.
Mar.
Foggy month along china coast
Many research on circulation background, meteorology
conditions and numerical simulation of Qingdao sea fog
episode has been done （Wang，1983；Zhou et al.,2004;
Fu et al.,2004, 2006,2008; Gao 2007 ; Zhang et al. 2008）
There were only two sporadic reports about the microphysical observation of Qingdao sea fog （Yang 1985；
Xu et al. 1994 ) . Tri-purpose droplet spectrometer was
adopted to find the fog droplet information. We still have
knowledge on the aerosol size distribution and its induced
extinction.
It was found in guangzhou and other inland cities
that anthropogenic induced increase of fine
particles in atmosphere make the fog last longer
time and visibilities deteriorate （Wu et al.2007;Shi
et al.2008）.
Atmospheric aerosol in coastal city was determined by
prevailing wind direction and wind speed (Kim et al.
1995;Zielinski et al.,1997; Zielinski et al.2005).
The shift of Sea land breeze influence the size distribution
( Moorthy et al. 2003).
hygroscopic growth of accumulation mode particles
contribute to CCN number and the formation of fog and haze
（Johnson et al.2005; Swietlicki et al. 2008; Liu et al,2008；
Moon et al. 2007 )
Our aim
Analyze the variation of aerosol size distribution, and its impact on
the visibility during the forming, maintaining and enhancing stage
of the fog.
Data source
GOOS(Global Ocean Observing System)
—daily average sea surface temperature
model
NCEP FNL — global reanalysis data
Fog evolution
MTSAT-1R —visible satellite cloud map
SCRTWP-01 —wind profile radar. Resolution, 5min.
Wind variation
120m；
Temperature
GFE(L)1,GTS1—radiosonde，two times per day
humidity
FD12 —visibility meter , Resolution, 15s
visibility
GRIMM 180 —particulate monitor,32 intervals，frequncy
5min.
Aerosol size distribution
WRF
wind profile radar
(120ºº14´
14´E,36º
E,36º20´
20´N)
Radiosonde
GRIMM 180
FD12
(120ºº20´
20´E,36º
E,36º04´
04´N)
Sketch map of the observation site and instrument
Formation and evolution of the fog
1.Measurement result
Fog duration time
vi si bi l i t y
Visibility(m)
22000
21000
20000
19000
Jul.7
Jul.8
Jul.9
18000
17000
16000
15000
14000
13000
12000
12:51-19:20
Jul.7
21:51-23:44
9:28-12:51
Jul.8
20:37-23:55
11000
10000
9000
8000
7000
6000
5000
4000
fog
fog
6:58-19:52
fog fog
Jul.9
Visibility duration fog
3000
2000
1000
0
4
424
844 1309 1729 2155 214
644 1104 1529 1949
14
434
904 1319 1739 2209
Local Time
Visibility change from Jul.7 to 9. 2008
168-1140m
Jul.7
347-1083m
Jul.8
125-1192m
Jul.9
MTSAT-1R satellite images（Beijing Time）
站长站素材 SC.chinaz.COM
www.nordridesign.cn
2. Meteorology condition
850hPa weather map at 08:00 Jul.6
North-east cold vortex ，
water vapor form southwest
The fog frequency is high in
upwelling area,where the sea
water temperature is low and
air-sea temperature difference
is large. (Leipper et al.,1994;
Cho et al.,2000; Tokinaga et
al., 2009)
SST on Jul. 6
朝鲜半岛西侧冷水域
7月
月7日
日14时
时
7月
月8日
日14时
时
副高西伸北抬
海风明显
相对
湿度
气温
440m海风层
Fog layer: >90%RH
wind speed
Relationship of atmospheric
aerosol concentration and
horizontal visibility
160
22000
vi si bi l i t y
concent r at i on
20000
Jul.7
Jul.8
Jul.9
120
16000
Visibility(m)
140
14000
100
12000
80
10000
60
8000
6000
40
1-2.5um particulate number
concentration
18000
4000
Good relationship was
found between the
occurring time of low
visibilities and number
concentrations of
coarse mode particles in
the 1-5µm size range.
20
2000
0
0
4
424 844 1309 1729 2155 214 644 1104 1529 1949 14
434 904 1319 1739 2209
Time
60000
200
Jul.5
Jul.6
Jul.7
Jul.8
Jul.9
Jul.10
1~5um
150
40000
30000
100
20000
50
10000
0
4 4 9 34 95 24 55 19 54 51 44 90 39 04 93 54 92 54 24 49 41 39 41 3
4 09 43 49 42 49 19 44
4 92 54 24 94 19 9
2 17 311 0
5 9 41 81 32 3 8 21 71 12 1 6 01 51 91
4 9 3
4 8 31 71 22 3
6
1 02
1 81 22 2 7 11 61 02
Local time(hhmm)
0
concentration(cm-3)
50000
coarse particulate number
fine particulate number concentration(cm-3)
<1um
An inverse correlation was identified between the visibility and the number
concentration of the particles in 1–2.5 μm. The visibility was much lower
and the dense fog would last much longer when the number concentration
of the particles in 1–2.5 μm was large.
Number concentration of different particles during fog and heavy fog weather
Fog
Strong fog
-3
Duration
number concentration(cm
<1µm
)
1~2.5µm
2.5~5µm
visibility(m)
521
12:51~19:20
5548.71
13.14
1.45
21:51~23:44
14798.71
22.15
1.13
9:28~12:51
6750.77
11.79
0.70
4092.32
12.38
1.18
5137.85
62.17
8.49
0:37~23:55
6:58~19:52
averaged
3
507 2
5
721
550 4
1
372
-3
Duration
number concentration(cm
<1µm
)
averaged
1~2.5µm
2.5~5µm
visibility(m)
13:00~19:00
5364.93
13.89
1.53
497
22:05~23:15
15067.43
27.65
1.59
336
11:00~12:20
6549.74
14.33
1.01
476
21:00~23:00
3923.92
13.99
1.55
486
8:30~19:47
4846.88
69.73
9.62
305
4092-14798
11-62
3923-15067
13-69
The number concentration of 1~2.5μ
μm particles was above 11.79/cm3
during the fog
• During the visibility degradation (from 10 km to 1 km)
process, the number concentration of the submicron
particles less than 0.5 μm increased more quickly, while
those in 0.5–1 μm increased slowly.
• Onset of the fog (visibility less than 1 km) was concurrent
with the abrupt increase of the number concentration of the
coarser particles in 1–5 μm, when the number
concentration of the particles in the Atiken nuclei range and
the accumulation range (diameter less than 1 μm) started to
decrease.
Size distribution of the
atmospheric aerosol
100000
a)
10: 00
13: 00
16: 00
19: 00
22: 00
10000
1000
3
-
)
m
c(
)r
(g
o
ld
/N
d
100
10
When the fog is forming, density of fine
particles below 1μ
μm decrease continuously,
however number concentration of particles
in 1-2.5μ
μm size range had a trend of
fluctuating growth, and its change period is
about 2.5h.
1
0. 1
0. 01
0. 1
1
Di amet er r ( um)
10
Size distribution at different
time on Jul.7
During the fog strengthening stage, the
number concentration of particles below
1μ
μm diameter was on a declining trend,
whereas the number concentration of
paticles above 1μ
μm diameter had a
increasing tendency.
When close to the fog decay time, there
was fast decrease of 0.5μ
μm-5μ
μm particles.
100000
b)
Jul . 6
10000
Jul . 7
Jul . 8
Jul . 9
1000
dN/ dl og( r ) ( cm )
By comparing size distributions of
three fog days, it is found that
Jul . 5
Jul . 10
3
-
100
10
1
0. 1
0. 01
0. 1
1
Di amet er r ( um)
Size distribution of different
days
10
When the fog was enhanced, particles
above 1μ
μm increased with the decrease of
particles less than 1μ
μm. But there was biomodal distribution in the submicron size
particles, 0.3-0.5μ
μm particles decrease ,and
0.5-0.7μ
μm particles increase，
，showing the
tendency of size shift from condensation
mode to droplet mode.
Compared with non-fog days, the
common feature in fog days is , number
of particles below 0.5μ
μm decrease，
，15μ
μm increase，
，and particles above 5μ
μm
was mostly removed
Meteorology data was analyzed to find the
reason of variation of aerosol size
distribution. The main factors are
Temperature
Humidity
Wind speed
Wind direction
Effect of humidity and temperature
Number concentration of particles below 1μm was
larger in high temperature and low humidity
conditions (Jul.5-Jul.7 and Jul.11) than that in low
temperature and high humidity conditions (Jul.8Jul.10)
the number concentration of the particles
corresponded very well with the specific humidity.
If the specific humidity increased continuously, the
number concentration of the particles larger than 1
μm would increase with high speed and large
amplitude, which would impact the visibility much
stronger. On the contrary, if the specific humidity
decreased continuously, the number concentrations
of the particles in 1–2.5 μm would reduce
accordingly, and the visibility would become better.
It seems that the number concentration of the
particles in 1–5 μm and the specific humidity were
two factors which play important roles in visibility
degradation and fog evolution.
Effect of wind
<1um
1- 2. 5um
25000
180
Jul.9
160
20000
140
120
15000
100
80
10000
60
Sea breeze brings coarse
particles . The predominant
modes of aerosols from the
sea was mostly in the 0.85μm size range in this sea
fog.
When there is wind shift from land
to sea, there is abrupt increase of
particles in 1-2.5μm size range,
which may caused by the
hygroscopic growth of polluted
land particles when meeting water
vapor and sea aerosol
40
5000
20
0
4 44 42
1
40 44 43 41 45 43 42 40 44 42 41 45
2 2 3 4 4 5 6 7 7 8 9 9
43 41 45 93 91 95 93 92 90 94 92 91 95
01 11 11 21 31 31 41 51 61 61 71 81 81
Size distribution and wind
profile on Jul.9
93 91 90 94 92 90 94
91 02 12 12 22 32 32
0
summary
The sea fog happened on July7-9 ,2008 in Qingdao was caused by
the co-effect of the Northeast cold vortex and subtropical high.
the fog easily formed in the layer with RH
≥90%, and wind speed ≤3m/s. It may arrive 530m altitude under
the help of sea breeze.
An inverse correlation was identified between the visibility and
the number concentration of the particles in 1–2.5µm. The number
concentration of 1-2.5µm particles was above 11.79/cm3 during
fog.
Different size particles have different change patterns during the
different stage of the fog.
It seems that the number concentration of the particles in 1–
5µm size range and the specific humidity were two factors
which play important roles in visibility degradation and fog
evolution.