Central Texas Haze on
March 14-17, 2002
Images
Description
Haze associated with elevated levels of fine particulate occurred in Central Texas over four days from Thursday, March 14, through Sunday,March 17, 2002. The highest measured PM2.5 daily average of 25.7 µg/m³ for March 17 at Austin Murchison CAMS 3 rated as Moderate on the U.S. Environmental Protection Agency (EPA) 
Air Quality Index (AQI) scale.
The PM2.5 with Components graph shows the hourly PM2.5 measurements from the two Austin PM2.5 sites — Murchison CAMS 3 and Audubon CAMS 38. This graph also shows experimental data from three new continuous speciated monitors located at TNRCC Headquarters, CAMS 92, in North Austin. The data from the experimental instruments has not been validated. These instruments monitor sulfate (SO4), nitrate (NO3), and carbon (C), including elemetal carbon (C Elem) and organic carbon (C Orgn). The PM2.5 March 17 graph shows five-minute average data for the same parameters for March 17 only.
Analysis of satellite imagery, wind flow, and PM2.5 regional patterns indicates that much of the PM2.5 observed on March 14 and 15 was probably smoke from agricultural burning in southeastern Mexico and Central America. In contrast, the PM2.5 on March 16 and 17 appears to be primarily from sources in the U.S. On March 16 and 17, winds were from the northeast, bringing in continental air from the midwestern U.S., and wind speeds were very light. The stagnation allowed regional and local air pollutants to accumulate.
The Visibility graph shows hourly measurements of PM2.5, visibility, and relative humidity from Austin area sites. Visibility is affected by the particulate levels and by the relative humidity. High levels of particulate in the air cause low visibilities and also high levels of relative humidty cause low visibilities. At relative humidities below about 80 percent, most of the visibility reduction is caused by particulate in the air.
