Ozone is found in two regions of the Earth's atmosphere, in the upper regions where it prevents damaging ultraviolet light
from reaching the Earth's surface, and ground level . Both ground level and upper region ozone has the same chemical
composition of (O3).
- Ozone is caused by the interaction of sunlight and nitrogen oxides
- When nitrogen oxide is present in the air, and sunlight hits the nitrogen oxide, this results in the creation of ozone
The 8-hour ozone standard was last revised October, 2015 from 75 to 70 parts per billion. EPA projects that the revision will result in a total of 241 non-attainment counties. The EPA communicated the following timing of the revision:
- Final nonattainment designations will be made in 2017 most likely based on 2014-2016 air quality monitoring
- Any states designated nonattainment from this revision must achieve attainment in the 2020 to 2037 timeframe
EPA Ozone (O3) Home Page:
Particulate matter is a term used to describe a mixture of a complex group of fine airborne solid particles and liquid droplets (aerosols) which includes components of nitrates, sulfates, elemental carbon, organic carbon compounds, acid aerosols, trace metals, and geological material.
EPA has developed two PM standard categories:
- PM10 which are particles with a diameter smaller that 10 micrometers and larger than 2.5 micrometers and are known as "Inhalable coarse particles," such as those found near roadways and dusty industries
- PM2.5 which are particles with a diameter smaller than 2.5 micrometers and are known as "Fine particles“
On December 14th, 2012 the EPA concluded a revision of the PM2.5 fine particle standard. The results of the revision include:
- Retained the 24-hour standard at 35 ug/m3. This was last revised in 2006.
- Strengthen the annual fine particle standard from 15 down to 12 ug/m3
- EPA modeling projects/estimates this revision will result in 66 non-attainment counties, however they will utilize a two-year review process and will finalize non-attainment designations by December, 2014.
- Adds a “heavily traveled road in large urban areas” monitor requirement which will require the re-location of 52 of the existing 900 monitors.
- The 12 ug/m3 standard is to be met by 2020, however states can request and an additional 5-year extension.
- State implementation plans (SIPs) are due 2018 that outline the steps that each state (in nonattainment) will take to meet the standard.
EPA Particulate Matter Home Page: