Fine particulate matter – defined as particles less than 2.5 micrometers in diameter – are an under-recognized type of air pollution.  Gregory Wellenius, from Brown University (Rhode Island, USA), and colleagues analyzed data from medical records of 1,705 patients admitted at a Boston hospital with neurologist-confirmed ischemic stroke in a ten-month period.  The researchers cross-referenced these incidents against reported fine matter concentrations were measured at a central monitoring station.  They found that short-term exposure to fine particulate matter – even at levels allowed by the EPA – can increase the risk of ischemic stroke. As well, the team also observed a linear relationship between higher particulate levels and increased risk of stroke, strongest within 12 hours of exposure.  In a separate study, Jennifer Weuve, from Rush University Medical Center (Illinois, USA), and colleagues analyzed data collected in the Nurses’ Health Study.  Between 1995 and 2001, 19,049 study participants ages 70 and older with no history of stroke began a study of cognition health: cognitive testing was done by telephone three times, with about two years between interviews.  The researchers tracked changes in cognition, looking for associations with airborne pollution.  Particulate matter was measured using EPA monitoring data, adjusted to estimate local exposure for each participant. The researchers observed that higher levels of long-term exposure to both fine and coarse particulate matter both associated with significantly faster cognitive decline.  The team reported that the associations were observed at pollution levels typical in many geographical areas.