U.S. Air Quality

Special Feature: Saharan Dust Reaching Florida, July 1 to 16

Introduction

On July 10th, Dr. Jill Engel-Cox mentioned increased AOD in Florida due to African particles transported across the ocean. This post comments on the transport of these particles to the United States, occurring from July 1st to July 16th. The data come from MODIS on Terra and Aqua. They provide the Red Green Blue (RGB) images as well as the Aerosol Optical Depth (AOD) data. Some of the images are generated using HDFLook.

MODIS Aqua RapidFire image from 07-09-2004

Following the Saharan Dust

The season of African dust transport toward northern America usually lasts from June to October (CNN). The dust is transported by the Harmattan that blows during the dry season from the Saharan desert to the coast of West Africa. On July 1st, as seen on this MODIS AOD image, a plume of dust was exiting the African continent while one was already approaching Florida. The wunderground.com site reports winds with maximum speed of 10 mph, blowing westward from Dakar, Senegal. The visibility at Las Palmas de Gran Canaria, Canary Islands, was only 4.9 miles but the maximum gust speed was 41 mph.

MODIS AOD - 07-01-2004

The color scale has been adjusted to roughly approximate the EPA AQI six-color scale. To know how to read similar images click here.
On July 9th, the particle concentration along the west coast of Africa, near Mauritania and Senegal, was very high reaching hazardous levels of 250.5 mg/m3 and more. Visibility in Nouakchott, Mauritania, was as low as 2.7 miles. Traces of the haze from Africa to Florida via the Caribbean islands are clearly visible on this particular day. The dust plume, observed on the 1st near the African coast, has reached the Caribbean. Notice the increasing Aerosol Optical Depth in northern Canada. This plume of aerosols was due to the intense Alaska/British Columbia fires that lasted for weeks during this summer. This event will be summarized in an upcoming special post.

3-layer composite of MODIS-Terra/Aqua AOD and MODIS-Terra RGB picture 07-09-2004

This is a three-layer composite of Terra and Aqua AOD maps added to a MODIS-Terra RGB image. The slightly elevated AOD on the Atlantic Ocean is due to dust blown from Africa. See layers separately: (Terra)(Aqua)(RGB). For description of AOD images see help files. The RGB image is generated using HDFLook. However see help files for description of similar images.
As Jill mentioned in her post, the increased AOD was in part due to Saharan dust reaching Florida. On the 11th, the elevated AOD concentration near the southeastern coast was clearly visible.

MODIS Terra AOD - 07-11-2004

On July 16th, there was still some lingering haze over the Atlantic Ocean, and a new plume was exiting the African continent. The Canadian smoke plume had already reached northern US and was headed to the southeast toward Maryland and Florida.

MODIS Terra AOD ? 07-16-2004

Click here to view a movie illustrating the transport of African dust from July 1st to July 10th.

Posted by Kamonayi Mubenga at January 10, 2005 12:22 PM