Contrary to popular belief, aerosols surprisingly have both negative and positive effects on global warming. According to NASA, aerosols cool the Earth's surface, because it reflects sunlight back to the atmosphere. This causes a cooling process, and is all determined by the aerosol size. An easy to see cooling process are the various clouds in the sky. Clouds are formed by aerosol particles; the more aerosol particles, the heavier cloud, thus rainfall.
Now, on to the popular part. Aerosols are famously known for being "bad" and "harmful" to the atmosphere. That is correct, but only when there's an increase in carbon dioxide. This is usually from human activity, which started around 1000-2000 years ago, when life started to become a thing on Earth (ncdc.noaa.gov). The build up of carbon dioxide in the atmosphere traps other gasses from leaving, causing the greenhouse effect, thus a warmer Earth.
