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Seasonal Airmass Transport to the US
Big Bend, TX
Big Bend, TX
January
July
Prepared by: Rudolf B. Husar and Bret Schichtel
CAPITA ,Washington University, Saint Louis, Missouri 63130
Submitted to:
Angela Bandemehr
May 5, 2000, Draft
Contents
• Introduction
• Transport Climatology of North America
• Back-Trajectory Calculations to the U.S.
– Methodology
– Seasonal back-trajectories to 15 receptors
• Transcontinental Transport Events: Dust and Smoke
• Summary
Introduction
•
Anthropogenic and natural pollutants generated in one country are transported
regularly to other countries, adding to their air quality burden.
•
On average, the intercontinental transport of pollutants represents small additions to
US pollution burdens, but under favorable emission and transport conditions it may
elevate pollutant levels for brief periods.
Goal of Work:
•
To illustrate the paths air masses take during transport to the United States
•
The current approach relies on the calculation of backward airmass histories from 15
receptor points in the US, located mostly at the boundaries.
•
The transport analyses was conducted over the entire calendar year 1999, aggregated
monthly to illustrate the seasonal pattern of transport to each location
•
This work is a spatial and temporal extension of the previous airmass history analysis
for Spring 1998.
Transport Climatology of North America
• To be completed
Features of Air Flow over North America
• Major pathways of air masses affecting North America
Seasonal Air Flow
over North America
January
NAVAIR, 1966
July
April
October
Back-Trajectory Calculations to the U.S.
Methodology – Airmass Histories
• An airmass history is an estimate of the 3-D
transport pathway (trajectory) of an airmass prior to
arriving at a specific receptor location and arrival
time.
• Meteorological state variables, e.g. temperature and
humidity, are saved along the airmass trajectory.
• Multiple particles are used to simulate each airmass.
Horizontal and vertical mixing is included; particles
arriving at the same time to follow different
trajectories.
• Back trajectories incorporate the transport direction,
speed over source regions and dilution
The history of an airmass
arriving at Big Bend on 8/23/99
FNL Meteorological Data Archive
The FNL data is a product of the Global Data Assimilation System (GDAS), which uses
the Global spectral Medium Range Forecast model (MRF) to assimilate multiple sources
of measured data and forecast meteorology.
• 129 x 129 Polar Stereographic Grid with ~ 190 km
resolution.
• 12 vertical layers on constant pressure surfaces
from 1000 to 50 mbar
• 6 hour time increment
• Upper Air Data: 3-D winds, Temp, RH
• Surface Data includes: pressure, 10 meter winds,
2 meter Temp & RH, Momentum and heat flux
• Data is available from 1/97 to present.
Methodology: Airmass History Analysis
For details see: Springtime Airmass Transport Pathways to the US
Airmass history (Backtrajectory) Analysis
• Backtrajectories are aggregated by counting the hours each ‘particle’ resided in a grid cell.
Methodology –Residence Time Probability Field
• The grid level residence times hours are divided by the total time the airmasses reside over the entire domain and the
area of the grid cell.
• The resulting probability density function identifies the probability of an airmass traversing a given area prior to
impacting the receptor.
• The residence time probability fields are displayed as isopleth plots where the boundary of each shaded region is
along a line of constant probability. The red shaded areas have the highest probability of airmass traversal and the light
blue areas have the smallest probability.
• The most probable pathways of airmass transport to the receptor are along the “ridges” of the isopleth plot.
The probable airmass pathways to the Seattle, WA
receptor site
Residence Time Analysis: A 2 Dimensional Approach
• The residence time analysis does not account for the height of the airmass, nor
does it account for removal processes.
• Air masses travelling above the planetary boundary layer cannot accumulate
surface level emissions in source regions; likewise, they cannot affect receptor
sites.
• Back trajectories tend to increase in height with increasing age
Seattle, WA Particle Height Distribution
Airmass History Database
• 15 receptor sites were placed primarily along
the United States border
• Ten day airmass histories were calculated
every two hours during all of 1999.
• 25 particles were used to simulate each
airmass trajectory
•Temperature, Relative Humidity, and Precipitation rate, were also saved out along
each trajectory.
•Airmass histories were calculated using the CAPITA Monte Carlo Model driven by the
FNL global meteorological data.
• This system was previously validated for hemispheric transport by simulating the
April 1998 Chinese Dust Event.
1. Aleutian Islands, AK
January
April
July
October
The Aleutian Islands are affected by air masses coming from all directions throughout
the year.
However, air masses affecting the Aleutian Islands appear to come preferentially from
the west.
1. Aleutian Islands, AK
January
April
July
October
The Aleutian Islands are affected by air masses coming from all directions throughout
the year.
However, air masses affecting the Aleutian Islands appear to come preferentially from
the west.
2. Point Barrow, AK
January
April
July
October
Pt. Barrow is affected strongly by air masses passing over the Arctic Ocean
throughout the year.
Transport of air masses from the southwest occurs- except during winter.
2. Point Barrow, AK
January
April
July
October
Pt. Barrow is affected strongly by air masses passing over the Arctic Ocean
throughout the year.
Transport of air masses from the southwest occurs- except during winter.
5. Seattle, WA
January
April
July
October
Seattle, WA is affected by air masses coming mainly from the west throughout the
year.
6. San Francisco, CA
January
April
July
October
San Francisco, CA is affected by air masses coming mainly from the west
throughout the year.
9. San Diego, CA
January
April
July
October
San Diego is affected by air masses coming mainly from the
Northwest throughout the year.
10. Big Bend, TX
January
April
July
October
There are large seasonal differences in the directions that air masses arriving in
Big Bend, TX have taken.
During winter and into spring, they come from the west and the northwest,while
11. N. Minnesota, MN
January
April
July
October
Northern Minnesota is affected mainly by air masses coming from the north and the
northwest throughout the year.
During the summer, transport from the west and the south also occurs.
12. St. Louis, MO
January
April
July
October
St. Louis, MO is affected by air masses coming from the north and northwest
throughout the year.
However, this pattern shifts so that St. Louis is more strongly affected by air
13: Everglades, FL
January
July
April
October
Southern Florida is affected by air masses coming from the northwest during the cooler months of the year.
In contrast to the northern United States, southern Florida is strongly affected by air masses coming from
the east, especially during summer.
These air masses transport dust from North Africa to the southern United States.
14: Rochester, NY
January
July
April
October
Rochester, NY is affected by air masses coming from the north and northwest
throughout the year.
Transport from the south becomes more important during the summer.
15: Burlington, VT
January
July
April
October
Burlington, VT is affected by air masses coming from the north and the northwest in
all seasons of the year.
During the summer, transport from the south increases in importance.
Intercontinental Transport Events: Dust
• Satellites have found convincing evidence for the transport
of dust between continents.
• Dust from the Gobi and Taklamakan Deserts in Asia and
The Asian Dust Event of April 1998
Mongolia
China
Korea
On April 19, 1998 a major dust storm occurred over the Gobi Desert
The dust cloud was seen by SeaWiFS, TOMS, GMS, AVHRR satellites
The transport of the dust cloud was followed on-line by an an ad-hoc
international group
Trans-Pacific Dust
Transport
It took about 4 days for the
dust cloud to traverse the
Pacific Ocean, at an altitude
of about 4 km
As the dust approached N.
America, it subsided to the
ground
Asian Dust Cloud over N. America
Reg. Avg. PM10
100 mg/m3
Hourly PM10
On April 27, the dust cloud arrived in North America.
Regional average PM10 concentrations increased to 65
mg/m3
In Washington State, PM10 concentrations briefly
Smoke from Central American Fires
May 14, 98
Smoke from Central American
Fires
DMSP – Night Light
May 15, 98
SeaWiFS, TOMS, Bext May 15,
1998
Smoke Aerosol and Ozone – Inverse Relationship
Extinction Coefficient (visibility)
Surface Ozone
Surface ozone is generally depressed under the smoke cloud
Summary of Global Air Pollution and Transport
•
The global sulfur emissions have shifted from N. America and Europe to East Asia.
•
The industrial ‘belt’, 30-60 deg N, is dominated by anthropogenic SOx, NOx and O3.
This conforms to the conventional wisdom since the 1970s.
•
Recent satellite data show that NOx, HC and aerosols are dominated by biomass
burning in the subtropics and the southern hemisphere. ??
•
The radiatively active global aerosol is dominated by smoke and dust, rather then by
industrial sulfates as we have presumed.
•
Episodic trans-continental transport of dust and smoke (ozone?) can now be detected
and modeled routinely.
•
Such extra-jurisdictional ‘pollution’ events cause significant episodic impact on the air
quality of N. America.
Source Impact of Pollution and Dust/Smoke Events
• Two key measures of source impacts are on the
concentration and dosage at the receptor
• Both depend on the source strength as well as the
atmospheric transmission probability
• Long-term, average pollution emission rates are
relatively low (say E=1) compared to dust/smoke
events (E = 100) but they are continuous (L= 1),
whereas emissions causing the dust/smoke events
are intermittent (L=0.01)
• Dust/smoke events produce high short-term
concentration peaks at the receptor that are easily
detectable.
• Over longer periods, the effects of long-range
transport of pollutants are difficult to detect
because the receptor concentrations are low.
• However, the long-term dosage from the two
types of sources may be similar.
•Rudy, are you familiar with potential source
Example Concentration/Dosage Calculation
The impact of the emission from source i, Ei, on the
concentration at receptor j, Cj , is determined by
the transmission probability, Tij :Cj = Tij Ei
The dosage is the integral of the concentration over
the time length, Li, Dj = Li Cj
Emission Rate:
Transmission:
Emission Length:
Cj = 1 x 1 = 1
Dj = 1 x 1 x 1 = 1
Pollution
Ei = 1
Tij = 1
Li = 1
Dust or Smoke Event:
Emission Rate:
Ei = 100
Transmission:
Tij = 1
Emission Length:
Li = 0.01
Cj = 100 x 1 = 100
Dj = 100 x 1 x 0.01 = 1
Summary (tentative)
• Air masses reaching the boundaries of the United States arrive from
different directions
• However, each receptor location has a climatologically well defined
seasonal pattern of air mass history
• Alaska is affected by air masses coming mainly from the west
• Northern California, Oregon and Washington are affected mainly by air
masses coming from the west throughout the year.
• Air masses arriving at the above locations have the highest probability
of passing over Asia during the ten days prior to arrival.
• Southern California is affected by air masses coming from the west
northwest.
• The central United States is affected by air masses coming mainly from
the northwest during the cool months and from the south during the
summer.
• The southeastern United States is affected by air masses coming from
the north in the cold season and from the southeast during the warm
season.
• The northeastern United States is affected by air masses coming from
the Arctic, the Pacific Ocean and the Tropics
•
•
•
•
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Hemispheric option – full context?
Half-hemispheric option-better proportions?
What do you think?
Note: there is a bit of a gap at the datelineproblem with the splicing.
Also, the fine features of the transport pattern
an not too meaningful
• - applicable only to 1999
• - vertically integrated, not surface
transport
Polar Stereographic Projection
•
•
•
•
Joe, this projection always confuses me…
It is a nice projection for meteorologists but for policy types?
R
Rudy, I think this projection will work better for Pt. Barrow and maybe