Southern Texas Saharan Dust June 28 - July 2, 2008

• Backward Air Trajectory 28th
• Backward Air Trajectory 29th
• Backward Air Trajectory 30th
• Backward Air Trajectory 1st
• Backward Air Trajectory 2nd
• Satellite Image Gulf of Mexico 26th 5:08 pm CDT
• Satellite Image Gulf of Mexico 27th 5:08 pm CDT
• Satellite Image Gulf of Mexico 28th 5:08 pm CDT
• Satellite Image Gulf of Mexico 29th 5:08 pm CDT
• Satellite Image Gulf of Mexico 30th 5:08 pm CDT
• Satellite Image Gulf of Mexico 1st 5:08 pm CDT
• Satellite Image Gulf of Mexico 2nd 5:08 pm CDT
• Satellite Images Tracking Dust from Africa (download PowerPoint file)
• Daily Midday PM2.5 and Wind Plots

Description
A large Saharan dust cloud began moving into South Texas on Wednesday, June 28th and spread northward into Central and Southeast Texas on June 29th.   The dust continued over most of the southern half of the state through July 1st and continued in Southeast Texas through July 2nd.   A weak cold front across the middle of the state prevented the dust from moving farther north.

  The highest daily average PM2.5 measurement during this event was 27.5 micrograms per cubic meter (µg/m³) at the Galveston Continuous Ambient Monitoring Station (CAMS) 1034 on July 1st.   This measurement rated as Moderate, on the U.S. Environmental Protection Agency (EPA) Air Quality Index (AQI) scale.   PM2.5 measurements were in the "Moderate" range across most of the affected areas on all five days.   Hourly PM2.5 measurements were generally in the 20 to 40 µg/m³ range because of Saharan dust in the affected areas, with higher spikes from local influences at some sites.   Speciated PM2.5 measurements were only available from a few sites in the southern half of the state on the 29th, but all of the measurements in this area showed highly elevated levels of silicon indicating dust dominance, ranging from 1.3 µg/m³ at Brownsville to 2.3 µg/m³ at Deer Park.   Deer Park also had a silicon measurement of 1.8 µg/m³ on July 2nd.

Backward air trajectories indicate that the air came across the Atlantic Ocean.   Satellite imagery indicates that the dust cloud began emerging from the coast of Africa on June 18th, reached the Lesser Antilles on June 23rd, and began moving into the Gulf of Mexico on June 26th.   Satellite imagery shows that the dust cloud covered the entire Gulf of Mexico on June 28th.