Global and Local Dust over North America

Initial Assessment by a Virtual Community on Dust

http://capita.wustl.edu/NAMAerosol/NAMDust

Coordinated by R. B. Husar CAPITA, Washington University, St. Louis, MO

Presented by Bret SchichtelCIRA, Colorado State U., Ft. Collins

Prepared for Presentation at the AWMA/AGU Conference

Regional Haze and Global Radiation Balance - Aerosol Measurements and Models

October 2-5, 2001 • Bend, Oregon

Objectives and Approach to Integrated Analysis

Objectives • Establish the spatio-temporal and chemical pattern of the airborne dust over North America

• Characterize the features of dust from the different sources

• Attribute the dust over NAM to the major source regions

Approach• Integrate data from surface and satellite observations

• Combine spatial, temporal and compositional analysis

• Invite the community to actively particulate in conducting this open, integrative analysis

Status (September 2001)

• Recent data from several satellite and surface sensors were analyzed and presented

• The data and knowledge from the literature has not yet been incorporated

• An open discussion and interaction with the community begun in October 2001

Applications of Integrated Analysis• NARSTO-PM Assessment,

• Monitoring Network Design/Evaluation;

• MODELS-3 Evaluation;

• Regional Haze Management

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.

• New satellite sensors allow monitoring the spatial and temporal pattern of dust events on a daily basis.

Composition of Asian & Saharan Dust

African and Asian dust over NAM differ in elemental ratios

The differences can be used to apportion the NAM dust

Aluminum/Silicon

Average Elemental Ratios

Dust Particle Size and Shape

Irregular Shape 30-40% of long range dust mass < 2.5 m

Long range dust Mass mean D is 2-5 m

The near source dust MMD is >5 m

Transport Climatology of NAM

The main transport winds are zonal westerlies at mid-latitudes, zonal tropical easterlies and north-south excursions

The Cordillera, mountain range is a significant obstacle to the zonal westerly and to the easterly trade winds.

( Based on Bryson and Hare, 1974)

Airmass Transport Example

Summer airmasses are from the east

Winter airmasses are from the west

Big Bend, TX

Sahara Dust Transport Across the Atlantic

• Data from the LITE space-born lidar instrument show that a large fraction of the Sahara dust travels across the Atlantic in elevated layers (up to 5km).

• However, surface measurements along the dust track also show ground-level dust throughout the dust path indicating settling and entrainment into the marine BL

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

The TOMS Absorbing Aerosol Index in July shows the Sahara dust plume over the Atlantic and the Gulf Coast

Satellite Data on Sahara Dust

Sahara Dust

Sahara Dust

Previous work by Prospero, Cahill, Malm …has shown Sahara dust intrusions to the EUS

Based on EPA FRM PM10 data during episodes, the regional-scale PM10 concentration over the Gulf Coast exceeds > 80g/m3

Speciated PM (IMPROVE, Sisler & Malm, ) show that the highest annual fine dust (>1 g/m3) is over W. Gulf Region.

Sahara Events over the Eastern US: PM10

Attribution of Fine Particle Dust: Local and Sahara

Chemical Apportioning based on IMPROVE data (Si/Al Ratio)

In Florida, virtually all the Fine Particle Dust appears to originate from Sahara throughout the year

At other EUS 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.m3

In July the Sahara dust contribution is 4-8 g.m3, well in excess over the local contributions.

JulyAnnual

Asian Dust over North America

• Asian dust is generated during the Spring over the Gobi and surrounding deserts

• The Gobi dust clouds frequently traverse the Pacific and and a fraction reaches North America

• Multi-year satellite data from the AVHRR sensor shows a pronounced springtime Asian aerosol plume (dust, smoke and industrial haze)

• The springtime Asian plume optical thickness is about 0.3

The April 1998 Asian Dust Event

Approximate location of the April 19 1998 dust cloud over the Pacific Ocean based on daily SeaWiFS, GMS5/GOES9/GOES10 and TOMS satellite data.

GOES 10 satellite image of the he bright, reflecting dust over Western NAM, April 27.

Contour map of the PM10 on April 29, 1998 shows >100 g/m3 over Washington State.

The peak of regional average PM10 concentration over the West Coast on April 27-30 is due to the Asian dust.

The Asian Dust Event over NAM: A Spatial Perspective

Based on IMPROVE, on April 29, 1998 the fine particle dust concentration increased to about over 10 g/m3 at 7 Western US sites.

A long-term apportioning the Asian and local dust over the West Coast would be most interesting.

Local Dust Emitted over over the North America

Features of the ‘Western Dust ‘Bowl’?

• Spatially homogeneous, well mixed dust concentration (Arizona-Idaho)

• Relatively low coarse dust concentration - small particle size (4-8 um MMD)

TOMS Absorbing Aerosol Index• TOMS satellite data indicate

elevated dust aerosol to the East and West of the Rocky Mountains

• The source of the dust in the intermountain plateau and W. Texas need to be characterized

‘Western

Dust Bowl’

Summary – Invitation to Participate

• There is considerable research literature on the dust aerosol pattern and characteristics over North America.

• However, both the recent satellite and previous research is fragmented, and uneven in spatial, temporal an compositional coverage.

• The dust research community is invited to actively particulate in conducting an integrative analysis.

See you on the web.

http://capita.wustl.edu/NAMAerosol/NAMDust