Air quality in Boston is generally very good: during the ten-year period 2004–2013, there were only 4 days in which the air was unhealthy for the general public, according to the EPA.
২০০৪ থেকে ২০১৩ সালের মধ্যে কত দিন বায়ু অস্বাস্থ্যকর ছিল?
4 days