They noted that probably due to prevailing wind patterns in the area studied, the levels of particulate matter -- a type of air pollution from man-made or natural sources consisting of tiny solid or liquid particles that can cause health problems when inhaled -- were relatively low.

"The vast majority of the public is exposed to ambient air pollution at the levels observed in this community or greater every day, suggesting a potentially large public health impact," lead study author Lynda Lisabeth of the University of Michigan School of Public Health in Ann Arbor said in a statement.

The study, published in the Annals of Neurology, is based Brain Attack Surveillance in Corpus Christi Project records of all ischemic stroke and transient ischemic attack cases from 2001 to 2005 in Nueces County, Texas.

Comparing this data with the air pollutant and meteorological daily measurements from the Texas Commission on Environmental Quality's Monitoring Operations database, the researchers found borderline significant associations between same day and previous day fine particulate matter exposures and ischemic stroke/TIA cases -- with the majority of cases located upwind of local chemical plants and refineries.