Almost every year, Texas experiences hazy skies for a few days or weeks in the Spring and Summer. The sky can look hazy and your favorite landmarks can be harder to see. Let’s talk about that haze, where it comes from, and the potential impacts to Houston’s air quality.
The main cause of this haze is smoke transported across the Gulf of Mexico from agricultural fires in Mexico and Central America.
Open burning of crop residue is a method used by growers around the world to improve yields, reduce the need for herbicides and pesticides, reduce fire hazards, and control disease, weeds, and pests. It’s cheap and easy to do, and particularly for farmers in countries that don’t have many other options to prepare their land for planting, it can be very helpful.
Unfortunately, there are two big disadvantages to agricultural burning. First, fire is unpreditable and it can spread and spark wildfires. Second, the smoke produced by these fires can raise air pollution levels and potentially impact human health, even hundreds of miles away. Smoke reaches the U.S. from Central America when upper level winds transport it northward.
In Texas, we have been seeing the effects of the burning season in Mexico and Central America on Southeast Texas. Most years, this drifting smoke elevates fine particle and ozone levels across Houston and South Texas but does not create a significant public health threat. One year, however, smoke concentrations caused ozone pollution to increase, resulting in a public health threat. During the period from April 1, 1998 through June 20, 1998, large amounts of smoke were transported into Texas from fires in Mexico and Central America. These fires were unusually intense and widespread because of severe drought conditions. The smoke also produced high levels of ozone and carbon monoxide. These pollutants accompanied the smoke into Texas. The image below shows the intensity of the smoke during this episode.
Source: NASA’s Goddard Space Flight Center at www.gsfc.nasa.gov
Clouds show up in the SeaWiFS image as bright white, the smoke plumes and haze are a light tan. In some cases, you can see the smoke plumes streaming off the Yucatan coast. The other two images represent alternate views of the smoke and its components.
By May 1998, smoke intensity climbed to levels that could threaten public health. Concerned by this threat, the Texas Natural Resource Conservation Commission (the predecessor agency to the Texas Commission on Environmental Quality (TCEQ)) stepped up its air quality monitoring activities and worked with the news media and other governmental agencies to make the public aware of dangers posed by these smoke levels. They shifted additional ground monitors into the Rio Grande Valley and made numerous flights with an airborne air pollution monitor. Local schools and the Texas University Interscholastic League even cancelled and relocated outdoor sports at times, the smoke was so severe.
After the episode, TCEQ performed a comparison analysis of air pollution on a smoke day (May 8th) to a non-smoke day (October 3rd) with almost identical weather conditions in Brownsville. It showed that ozone, carbon monoxide, and particulate levels were much higher on the smoke day. Ozone levels on the smoke day reached 1-hour values near 100 parts per billion, whereas on the non-smoke day the ozone peaked at only 20 parts per billion. 80 parts per billion from long-distance smoke is quite an impact! As a result of the analyses performed by TCEQ, it was determined that smoke from the fires in Mexico actually created several days of increased ozone pollution in Houston that spring.
If you want to keep close track of these events as they occur, TCEQ maintains an air pollution forecast page here http://www.tceq.texas.gov/airquality/monops/forecast_today.html that you can sign up to receive each week.
For More Information:
The Texas Department of Agriculture and TCEQ have adopted rules and guidelines for farmers and ranchers that want to use burning as a part of their agricultural management plan. You can learn more about Texas’ rules here. http://www.texasagriculture.gov/home/productionagriculture/prescribedburnprogram.aspx
Learn more about how NASA tracks fires and weather events through their satellite research program at: http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MOD14A1_M_FIRE