When the New York City medical examiner decided last week that Felicia Dunn-Jones’s death was directly linked to the dust of the destroyed twin towers, making her the 2,750th victim of the attack on Sept. 11, Mrs. Dunn-Jones’s husband, Joseph, was relieved beyond words.

But while that decision brought some comfort to Mr. Jones, who had fought for three years to have his wife’s name added to the city’s official list of victims, it is likely to have an unsettling effect on thousands of other people who also came into contact with the dust on Sept. 11 and in the days after.

Many New Yorkers who breathed in the dust were not responders who rushed to help at the disaster site but were office workers like Mrs. Dunn-Jones, a 42-year-old lawyer whose office was a block from the trade center. She developed a troubling cough weeks after fleeing the attack and died in February 2002.

Many other people who were working downtown that morning were also engulfed by the roiling plume of dust, smoke and ash. Thousands of schoolchildren and people living in as many as 30,000 apartments and condos in Lower Manhattan also breathed in some of the dust as they escaped that day.