2004-10-28 Intercontinental Dust and Smoke over North America:Quantitative Tools an Results

The Dust Community

Intercontinental Dust and Smoke over North America:Quantitative Tools an Results

??July Dust

Local Sahara Dust

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Observational Tools Establishing Aerosol Origin (Egen, 1835)

Direct Evidence

Spatial Pattern Wind Pattern

Composition Temporal Pattern

Trajectory

Modern Methods – similar to century-old approaches but with more data

• Direct Evidence. Photographic, satellite or compelling visual evidence of origin• Aerosol Composition. Chemical fingerprinting of different source types (speciation, traces)• Temporal pattern. Chemical Physical property analysis (satellite, ASOS, PM2.5)• Spatial Pattern. Chemical• Transport Pattern. Forward, backward trajectory, residence time analysis • Chemistry with Transport. Combining chemical fingerprinting and transport (CATT) • Dynamic modeling. Simulation model (forward, inversion) quantifying origin/transport

Historical Methods

• Source attribution methods have been used for the past 2 centuries

• A list of methods was given my Egen, 1835. See paper and PPT

Satellite Observation of Sahara Dust (SeaWiFS)

• The SeaWiFS satellite provides ‘truecolor’ images of the Sahara dust as it approaches (July 21, 1998) and covers part of the continent (July 24).

• Such SeaWiFS and other satellite data allow daily dust tracking as well as climatological dust studies.

• Sahara dust has also been frequently photographed over the Caribbean by the astronauts.

Origin of Fine Dust Events over the US

Gobi dust in springSahara in summer

US-scale fine dust events are mainly

from

intercontinental transport

Fine Dust Events, 1992-2003ug/m3

Attribution of Fine Particle Dust: 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

Sahara and Local Dust Apportionment: Annual and July

• The maximum annual Sahara dust contribution is about 1 g.m 3

• 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 respect ive Al/Si ratios.

• In July the Sahara dust contributions are 4 -8 g.m 3

• Throughout the Southeast, the Sahara dust exceeds the local source contributions by w wide margin (factor of 2 -4)

Annual July

Combined Aerosol-Trajectory Tool (CATT)

• High dust concentration (>7 ug/m3) in July all originate from Sahara

• Lower concentration form local sources

Seasonal Average Fine Soil (VIEWS database, 1992-2002)

• Fine soil concentration is highest in the summer over Mississippi Valley, lowest in the winter• In the spring, high concentrations also exists in the arid Southwest (Arizona and Texas)• Evidently, the summer Mississippi Valley peak is Sahara dust while the Spring peak is from local

(and Asian) sources

Sahara

Sahara Dust Impact EventsAIRS PM10 Concentration

July 5 1992 June 30, 1993 June 21, 1997

Eastern US PM25 Event Composition

• The largest EUS PM25 events (as RCFM) are simultaneously ‘events’ in sulfate, organics and soil!

• Some EUS PM25 events are single species events

• Some PM25 events are not events in any species; their reinforcing combination causes the PM25 event

Aerosol Event Catalog: Web pages

• Catalog of generic ‘web objects’ – pages, images, animations that relate to aerosol events

• Each ‘web object’ is cataloged by location, time and aerosol type.

Summary of Quantification Techniques

Intercontinental Transport Analysis Methods

• Direct evidence – satellite images

• Chemical tracers of Sahara, Gobi & Local dust (Al, Si, Fe, K)

• Temporal analysis – spikes are IC transport events

• Spatial analysis – excess dust in the dust transport path

• Spatio-temporal-chemical analysis with backtrajectories

Results• The chemical, temporal and spatial analyses indicate a consistent

estimate of 0.3 ug/m3 (2 ug/m3 in July) of fine dust over the SE US.