2003-10-10 measurement of free iron content in desert dust : effect on light absorption, and soil...
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Global and Local Dust over N. America Observations and Analysis Tools
Rudolf Husar
CAPITA, Washington University, St. Louis
Presented at:
Second Workshop on Mineral DustParis, France, September 10-12, 2003
Global Aerosol: Dominance of Dust, Smoke & Some SulfateNote: Each satellite senses different aerosol parameter, indicates different pattern
UV AbsorptionElevated Layer
Herman et. al., 1997
TOMS
POLDER
MISR
PolarizationSmall Particles
BackscatteringScattering Particles
Jun, Jul, Aug
Duze et. al., 1997
•Bad News:The mere characterization requires many tools. Some tools sample a small subset of the xDim aerosol data spaceThese need extrapolation, e.g. single particle analysis Other tools get integral measures of several dimensionsThese require de-convolution of the integral, e.g. satellite sensors
Aerosols: Many Dimensions• Compared to gases (X, Y, Z, T), the aerosol system has four
extra dimensions(D, C, F, M). – Spatial dimensions X, Y Satellites, dense networks– Height Z Lidar, soundings– Time T Continuous monitoring– Particle size D Size-segregated sampling– Particle Composition C Speciated analysis – Particle Shape/Form F Microscopy– Ext/Internal Mixture M Microscopy
Satellite-Integral
Aerosols: Opportunity and Challenge
• Good news: The aerosol system is self-describing. – Once the aerosol is characterized (size-composition, shape) and– Spatio-temporal pattern are established, – => The aerosol system describes much of its history through the
properties and pattern, e.g source type (dust, smoke, haze), formation mechanisms, atmospheric interactions. and transformations.
– The ‘aerosol’ dimensions (D, C, F, M) are most useful for establishing the sources and effects, including some of the processes.
– The Source of can be considered an additional, ‘derived’ aerosol dimension.
• Analysts challenge: Deciphering the handwriting contained in the data – Chemical fingerprinting/source apportionment– Meteorological transport analysis– Multidimensional data extrapolation, de-convolution and fusion
Dust Particle Size and Shape
• Near-Source dust mass mean diameter (MMD) is over 5-10 m, virtually all in the coarse mode
• Long range transported dust (3-10 days old) has MMD of 2-5 m, 30-50% of the mass in the PM2.5 range
Atmospheric Residence Time of Dust
• Coarse dust particles with 10 and and 100 m size, settle out within 1 day and 15 minutes, respectively.
• Fine dust particles are removed by clouds and rain
Residence Time in the Atmosphere (Jaenicke, 1978) 1 m ~ 15 days
100 m ~ 15 min
10 m ~ 1 day
PM2.5 Residence Time Increase with Height
• Within the atmospheric boundary layer (the lowest 1-2 km), the residence time is 3-5 days.
• Dust lifted to 3-10 km is transported for weeks over thousands of miles.
Local, Sahara and Gobi Dust over N. America
• The dust over N. America originates from local sources as well as from the Sahara and Gobi Deserts
• Each dust source region has distinct chemical signature in the crustal elements.
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Al/Si Fe/Si Ca/Si K/Si Ti/Si
Sahara SW US
The two dust peeks at Big Bend have different Al/Si ratiosDuring the year, Al/Si = 0.4 In July, Al/Si reaches 0.55, closer to the Al/Si of the Sahara dust (0.65-0.7) The spring peak is identified as as ‘Local Dust’, while the July peak is dominated by Sahara dust.
Attribution of Fine Dust (<2.5m) Local
and Sahara
• In Florida, virtually all the Fine Particle Dust appears to originate from Sahara throughout the year
• At other sites over the Southeast, Sahara dominates in July
• The Spring and Fall dust is evidently of local origin
Everglades, FLBig Bend, TX
Upper Buffalo, AK
Annual PM2.5 Mass
Seasonal Fine Aerosol Composition, E. USUpper Buffalo Smoky Mtn
Everglades, FLBig Bend, TX
Seasonal and Secular Trends of Sahara Dust over the US
Seasonally, dust peaks sharply in July when the
Sahara plume swings into the Caribbean.
Regional Sahara Dust events occur several times each summer
Sahara and Local Dust Apportionment: Annual and July
• The maximum annual Sahara dust contribution is about 1 g.m3
• In Florida, the local and Sahara dust contributions are about equal but at Big Bend, the Sahara contribution is < 25%.
The Sahara and Local dust was apportioned based on their respective source profiles.
• In July the Sahara dust contributions are 4-8 g.m3
• Throughout the Southeast, the Sahara dust exceeds the local source contributions by w wide margin (factor of 2-4)
AnnualJuly
Supporting Evidence: Transport Analysis
Satellite data (e.g. SeaWiFS) show Sahara Dust reaching Gulf of Mexico and
entering the continent.
The air masses arrive to Big Bend, TX form the east (July) and from the west
(April)
Sahara PM10 Events over Eastern USMuch previous work by Prospero, Cahill, Malm, Scanning the AIRS PM10 and IMPROVE chemical
databases several regional-scale PM10 episodes over the Gulf Coast (> 80 ug/m3) that can be attributed to Sahara.
June 30, 1993
The highest July, Eastern US, 90th percentile PM10 occurs over the Gulf Coast ( > 80 ug/m3)
Sahara dust is the dominant contributor to peak July PM10 levels.
July 5, 1992
June 21 1997
Sahara Dust Passage over the EUS (Poirot, 2003)Dirty dust composition based on Positive Matrix Factorization, PMF
At Brigantine, NJ, dust composition is enriched by SO4 (30% dirty dust mass) and NO3 (8%)
‘Dirty’ dust and salt composition
Weather Serv.
Upper Air Data
NOAA ARL
ATAD ATAD Traject
Gebhart (2002)
NPS-CIRA
IMPROVEData
PMF Tool
Pareto (2001) PMF “Sources”
Coutant (2002)
CATT Tool
Husar (2003)
Aggregation
Poirot (2003)
Direction of Dust Origin at 5 IMPROVE Sites
Ad hoc Data Processing Value Chain
High ‘dust’ concentration at 5 sites indicate the same airmass pathway from
the tropical Atlantic
Global Scale Dust Transport: The April 1998 Asian Dust EventLocation of the April 19 dust cloud over the Pacific Ocean
based on daily SeaWiFS, GMS5/GOES9/GOES10 and
TOMS satellite data.
The April 1998 Asian dust event caused 2-3 times higher dust concentrations then any other event during 1988-1998
Decomposition of Spectral Reflectance: Dust, Haze, Sea Water
1. The shape of dust, haze and sea reflectance are measured
2. The total spectral reflectance is measured
3. The dust, haze and sea reflectances are scaled to fit the total refl.
Topography: Sahara Dust Near the Surface
SeaWiFS shows a dense dust layer emanating from W. Africa
3D View
3D view shows that shallow islands are submerged in dust, while high islands extrude from the ~1 km deep dust layer
In West-Central Africa, winter haze is surface- based; summer haze is elevated
• In Jan-Feb the horizontal (Bext) extinction and vertical optical thickness (AOT) are correlated.
• This implies that the haze is surface-based and has a scale-height of of about 1 km.
• In Jun-Jul, the Bext is below detection limit, while the AOT is the same as in Jan-Feb.
• Evidently, the summer dust layer is elevated while the surface layer is dust-free.
Based on AERONET Sun Photometer Network, NOAA SOD Visibility data
Challenge:
Putting together theBIG PICTURE
‘Increasing amount of satellite-derived information about air, land and sea are helping scientists to study how they are interconnected to form a finely balanced system.’
National Geographic, Oct 2000
Will we be able to put together the Big Picture?
SUMMARY
• The atmospheric dust system occupies at least 8 key dimensions
g (x, y, x, t, size, comp, shape, mixture) • The current observational revolution (satellites, surface networks) allows monitoring many aspects of the global
daily aerosol pattern and transport.
• Each sensor/system measures different aspects of aerosols, usually resolving some and integrating over other dimensions.
• Data from multiple sensors/systems (satellites AND surface) along with models are required to characterize the 8D system and to derive actionable knowledge.
• Current data and analysis tools allow the estimation of transcontinental transport of dust to N. America.
• The yearly average fine (<2.5 um) Sahara dust concentration over the SE US is 0.2 – 1 ug/m3, with July peak concentration of 2-6 ug/m3.
• During specific transcontinental dust transport episodes from Africa and Asia, the globally transported surface dust concentrations approach 50-100 ug.m3 over 1000 km - scale regions of North America.
• These events constitute significant perturbations to the aerosol pattern of North America.
SUMMARY: New Opportunities
• We are in the midst of a sensory revolution regarding the detection of global aerosol sources, transport and some of the effects. Satellite and surface network provide daily pattern of aerosol.
• Still, the available aerosol data provides only a sparse characterization of the aerosol system.
• The Internet facilitates communication and the sharing, (reuse) of data and tools. There is a growing collaborative-sharing spirit in the scientific community; The winds of change are here – but we need to harness them for faster learning
• Establishing trans-continental source-receptor relationship for dust is attainable with available observational and modeling tools but will require:
– Open flow of data/knowledge and sharing of tools – Creation of scientific ‘value-adding chains’– Decomposition and reintegration of the 8D aerosol system