Current Air Quality Conditions are posted several times throughout the day and include information on Ozone and PM2.5. PM2.5 refers to fine particulate matter, which is a by-product of fossil fuel combustion. PM2.5 can easily reach remote lung areas, and is linked to serious respiratory ailments such as asthma and may aggravate other medical conditions. Ground-level ozone is not emitted directly into the air, but is created by chemical reactions in the presence of sunlight. Because of this, high ozone levels occur most frequently on hot summer afternoons. SJTPO engages in a number of efforts to measure and improve air quality in our region.