For the second time this week, some Lexington residents are being urged to avoid breathing outside air if possible on Saturday.
An air-quality advisory day is predicted. High temperatures and sunshine mean that ground-level ozone and particulate matter are likely to be high. The expected 113 reading on the air-quality index scale means the air could be unsafe for active children and adults and for others with chronic health conditions, such as asthma.
Air pollution generally is higher in the late afternoon and early evening.
An advisory had been issued for Monday, with a predicted reading of 106. Charles Schaub, a senior transportation planner with the city, said he is not sure that reading was reached, although preliminary indications are that it was not.
There were no alerts last summer.