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Chemical Hazard Explanation

Greenhouse gases describe chemicals that may increase the temperature of the Earth when present in sufficient quantities. Ozone is a molecule that forms smog near the ground, and it is formed by chemical reactions of greenhouse gases. Criteria pollutants are legally enforced by the Environmental Protection Agency; they include ozone and chemicals that pose public health threats when present in large quantities.

Greenhouse Gases

Adapted From: http://www.epa.gov/climatechange/ghgemissions/gases.html

Gases that trap heat in the atmosphere are called greenhouse gases. This section provides information on common greenhouse gases that are emitted from oil refineries and associated chemical plants.

Each gas' effect on climate change depends on three main factors:

How much of the gas is in the atmosphere?

Concentration, or abundance, is the amount of gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion. One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid (roughly the fuel tank of a compact car).

How long does a gas stay in the atmosphere?

Each gas can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. Gases mix in the atmosphere, meaning that the amount of gas measured at one point in the atmosphere is roughly equivalent to the amount of gas located anywhere else in the world, regardless of the source of the emissions.

How strongly does a gas impact global temperatures?

Some gases are more powerful than others at trapping heat and "thickening the Earth's blanket." The Global Warming Potential (GWP) describes how long a gas remains in the atmosphere on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy per pound and thus more greatly contribute to warming the Earth than gases with a lower GWP.

Criteria Pollutants

Adapted From: http://epa.gov/air/criteria.html

The Clean Air Act(1990) requires EPA to set National Ambient Air Quality Standards (40 CFR part 50) for pollutants considered harmful to public health and the environment. The Clean Air Act identifies two types of national ambient air quality standards. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants. Units of measure for criteria pollutant standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3).

National Ambient Air Quality Standards (NAAQS)

[final rule cite]
Averaging Time Level Form
Carbon Monoxide
[76 FR 54294, Aug 31, 2011]
primary 8-hour 9 ppm Not to be exceeded more than once per year
1-hour 35 ppm
[73 FR 66964, Nov 12, 2008]
primary and
Rolling 3 month average 0.15 μg/m3 (1) Not to be exceeded
Nitrogen Dioxide
[75 FR 6474, Feb 9, 2010]
[61 FR 52852, Oct 8, 1996]
primary 1-hour 100 ppb
98th percentile, averaged over 3 years
primary and
Annual 53 ppb (2) Annual Mean
[73 FR 16436, Mar 27, 2008]
primary and
8-hour 0.075 ppm (3) Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years
Particle Pollution
Dec 14, 2012
PM2.5 primary Annual 12 μg/m3 annual mean, averaged over 3 years
secondary Annual 15 μg/m3 annual mean, averaged over 3 years
primary and
24-hour 35 μg/m3 98th percentile, averaged over 3 years
PM10 primary and
24-hour 150 μg/m3 Not to be exceeded more than once per year on average over 3 years
Sulfur Dioxide
[75 FR 35520, Jun 22, 2010]
[38 FR 25678, Sept 14, 1973]
primary 1-hour 75 ppb (4) 99th percentile of 1-hour daily maximum concentrations, averaged over 3 years
secondary 3-hour 0.5 ppm Not to be exceeded more than once per year

as of October 2011. Source: http://epa.gov/air/criteria.html

  1. Final rule signed October 15, 2008. The 1978 lead standard (1.5 µg/m3 as a quarterly average) remains in effect until one year after an area is designated for the 2008 standard, except that in areas designated nonattainment for the 1978, the 1978 standard remains in effect until implementation plans to attain or maintain the 2008 standard are approved.
  2. The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for the purpose of clearer comparison to the 1-hour standard.
  3. Final rule signed March 12, 2008. The 1997 ozone standard (0.08 ppm, annual fourth-highest daily maximum 8-hour concentration, averaged over 3 years) and related implementation rules remain in place. In 1997, EPA revoked the 1-hour ozone standard (0.12 ppm, not to be exceeded more than once per year) in all areas, although some areas have continued obligations under that standard ("anti-backsliding"). The 1-hour ozone standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is less than or equal to 1.
  4. Final rule signed June 2, 2010. The 1971 annual and 24-hour SO2 standards were revoked in that same rulemaking. However, these standards remain in effect until one year after an area is designated for the 2010 standard, except in areas designated nonattainment for the 1971 standards, where the 1971 standards remain in effect until implementation plans to attain or maintain the 2010 standard are approved.

Ozone Forming Chemicals

Adapted From: http://www.epa.gov/airnow/aqi_brochure_08-09.pdf

What is ozone?

Ozone is a gas found in the air we breathe. Ozone can be good or bad, depending where it occurs:

Ozone is found at ground level and in the upper regions of the atmosphere (approximately 6 to 30 miles above the Earth's surface). Both types of ozone have the same chemical composition (O3). Upper atmospheric ozone protects the earth from the sun's harmful ultraviolet rays; ground level ozone forms a thick synthetic fog called smog.

Tropospheric, or ground level ozone, is created by chemical reactions between oxides of nitrogen (NOx), carbon monoxide (CO), and volatile organic compounds (VOC) in sunlight. Ozone is likely to reach unhealthy levels on hot sunny days in urban environments. Ozone travels long distances by wind, thus affecting areas that are not point sources. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major point sources of NOx and VOC.

Who is most at risk?

Several groups of people are particularly sensitive to ozone. Because ozone levels are higher outdoors, outdoor physical activity causes faster and deeper breathing, drawing more ozone into the body.

In general, as concentrations of ground-level ozone increase, more people begin to experience more serious health effects. Everyone should be concerned about preventing and responding to high ozone exposure.

What are the health effects?

Ozone affects the lungs and respiratory system in many ways. It can: