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

Sahara Local

Sahara Local

Global Aerosol: Dominance of Dust, Smoke & Some SulfateNote: Each satellite senses different aerosol parameter, indicates different pattern

UV Absorption

Elevated Layer

Herman et. al., 1997

TOMS

POLDER

MISR

Polarization

Small Particles

Backscattering

Scattering 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 space

These 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

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 Event

Location 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