Respuesta :
You most likely didn't find unhealthy concentrations of pm 2. 5 in the united states Because the United States is less populated.
The U.S. Environmental Protection Agency (EPA) tightened the national air quality standard for particulate matter pollution, revising the key annual PM2.5 standard to 12 micrograms per cubic meter (µg/m3), 6 Improved public health protection by extending 24 days a month - 3444 hours particulate matter standard 35µg/m3.
Exposure to particulate matter can cause premature death and adverse cardiovascular effects, such as heart attack and stroke, and is associated with a variety of other serious health problems. Particulate matter pollution also negatively impacts public welfare, creating a haze in cities and some of the United States' most prized national parks.
The EPA has issued a series of rules that provide significant advances in reducing pollution from particulate matter(PM2.5). These rules will help the majority of U.S. counties meet the revised PM2.5.
Learn more about EPA here: https://brainly.com/question/13699599
#SPJ4
