When talking about particle pollution, there are two sources of particles to consider: primary and secondary. Primary sources can cause particle pollution on their own because they are emitted directly from a source such as construction sites (CDC.gov). However, secondary sources make up the majority of fine particle pollution, forming “complicated atmospheric reactions involving chemicals such as sulfur dioxide and nitrogen oxides emitted by power plants, industries, and automobiles” (EPA.gov). Particles have the ability to remain in the atmosphere for days or weeks at a time, thus allowing pollution to spread widely and thus affecting air quality at an expansive rate. Areas most susceptible to high levels of particle pollution include urban and industrial areas (especially near busy roads), areas where there is smoke in the air from fireplaces, campfires or forest fires, and areas where the climate is calm and the air is often stagnant, allowing air pollution to accumulate (EPA.gov). Figure 2 below illustrates fine particle pollution concentrations in the United States