PM2.5 refers to a specific type of air pollution made up of particulate matter less than 2.5 micrometers in diameter (for context, a grain of fine sand typically measures about 90 micrometers wide). The tiny size of PM2.5 particles allows them to hang around in the air longer and makes them easy for us to inhale. This pollution can then penetrate deep into our bodies, increasing rates of heart and lung disease for those who experience long term exposure.
PM2.5 is released from a variety of sources including cars, trucks, and buses. While these sources may seem universal, communities' exposure to PM2.5 is highly unbalanced. In New York State, Asian American, Latino, Hispanic, and African American residents are all exposed to significantly more PM2.5 pollution than white residents.
Source: Union of Concerned Scientists, 2019. "Inequitable Exposure to Air Pollution from Vehicles in the Northeast and Mid-Atlantic." Link here.