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U.S. Environmental Protection Agency (EPA) . . . . . . . . . . . . . . . . . 241

National Ambient Air Quality Standards (NAAQS) . . . . . . . . . . . . 241

Air Quality Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Airborne Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

Liquids, Vapors, Aerosols, Sea Salt Mist

Table Classifying Chemically Active Contaminants: LiquidAerosols

Solid Contaminants

Table Classifying Airborne Particulates

Gas Contaminants

Table Classifying Reactive Environments & Terminology

8EnvironmentalMeasurement

HB envirochap8.qxd 3/2/2006 9:06 AM Page 239

U.S. Environmental Protection Agency

The U.S. Environmental Protection Agency is perhaps the single bestsource of information regarding environmental rules, regulations andtopics. EPAs mission is to protect human health and the environment.Readers seeking EPA-related information are encouraged to go to EPAsweb site:

http://www.epa.gov

All topics covered by EPA are listed alphabetically with links to locatedetailed information at:

http://www.epa.gov/ebtpages/alphabet.html

U.S. National Ambient Air Quality Standards

The U.S. Clean Air Act, last amended in 1990, requires the U.S. Envi-ronmental Protection Agency (EPA) to set National Ambient Air QualityStandards (NAAQS) for pollutants considered harmful to public healthand the environment. The Clean Air Act established two types ofnational air quality standards. Primary standards set limits to protectpublic health, including the health of sensitive populations such asasthmatics, children, and the elderly. Secondary standards set limits toprotect public welfare, including protection against decreased visibility,damage to animals, crops, vegetation, and buildings. The EPA Office ofAir Quality Planning and Standards (OAQPS) established NationalAmbient Air Quality Standards for seven principal pollutants, calledcriteria pollutants. They are listed in the following table. Units ofmeasure for the standards are parts per million (ppm) by volume, mil-ligrams per cubic meter of air (mg/m3), and micrograms per cubicmeter of air (g/m3).

Chapter 8/Environmental Measurement 241


242 ISA Handbook of Measurement Equations and Tables

1 Not to be exceeded more than once per year.2 To attain this standard, the expected annual arithmetic mean PM10 concentration at each monitor

within an area must not exceed 50 g/m3.3 To attain this standard, the 3-year average of the annual arithmetic mean PM2.5 concentrations from

single or multiple community-oriented monitors must not exceed 15.0 ug/m3.4 To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each pop-

ulation-oriented monitor within an area must not exceed 65 g/m3.5 To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone

concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm. 6 (a) The standard is attained when the expected number of days per calendar year with maximum

hourly average concentrations above 0.12 ppm is

Air Quality Index

The Air Quality Index (AQI) is an index for reporting daily air quality. Ittells how clean or polluted the air is, and what associated health effectsmight be a concern. The AQI focuses on why health effects might beexperienced within a few hours or days after breathing polluted air. EPAcalculates the AQI for five major air pollutants regulated by the CleanAir Act: ground-level ozone, particle pollution (also known as particulatematter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. An AQIvalue of 100 generally corresponds to the national air quality standardfor the pollutant, which is the level EPA has set to protect public health.AQI values below 100 are generally thought of as satisfactory. WhenAQI values are above 100, air quality is considered to be unhealthy atfirst for certain sensitive groups of people, then for everyone as AQI val-ues get higher. To make it easier to understand, the AQI is divided intosix categories:

Each category corresponds to a different level of health concern. Thesix levels of health concern and what they mean are:

Good The AQI value for your community is between 0 and 50. Airquality is considered satisfactory, and air pollution poses little or norisk.

Moderate The AQI for your community is between 51 and 100.Air quality is acceptable; however, for some pollutants there may bea moderate health concern for a very small number of people. Forexample, people who are unusually sensitive to ozone may experi-ence respiratory symptoms.


Air Quality Index(AQI) Values

Levels of Health Concern

Colors

When the AQIis in this range:

...air quality conditions are:

...as symbolizedby this color:

0 to 50 Good Green

51 to 100 Moderate Yellow

101 to 150 Unhealthy for Sensitive Groups

Orange

151 to 200 Unhealthy Red

201 to 300 Very Unhealthy Purple

301 to 500 Hazardous Maroon



Unhealthy for Sensitive Groups When AQI values are between101 and 150, members of sensitive groups may experience healtheffects. This means they are likely to be affected at lower levels thanthe general public. For example, people with lung disease are atgreater risk from exposure to ozone, while people with either lungdisease or heart disease are at greater risk from exposure to particlepollution. The general public is not likely to be affected when the AQIis in this range.

Unhealthy Everyone may begin to experience health effectswhen AQI values are between 151 and 200. Members of sensitivegroups may experience more serious health effects.

Very Unhealthy AQI values between 201 and 300 trigger a healthalert, meaning everyone may experience more serious health effects.

Hazardous AQI values over 300 trigger health warnings of emer-gency conditions. The entire population is more likely to be affected.


Airborne Contaminants

An ISA standard, ISA-71.04-1985, Environmental Conditions for ProcessMeasurement and Control Systems: Airborne Contaminants, classifiesairborne contaminants that may affect process measurement and con-trol instruments. The standard establishes airborne contaminantclasses for fixed (non-mobile) installations during normal operation(non-emergency conditions) or during transportation and storage. Theclassification consists of a class contaminant letter followed by a sever-ity identification numeral.

Airborne Contaminants Liquids, Vapors, Aerosols, Sea Salt Mist

Liquids This refers to liquids that will corrode unprotected equip-ment and are typically transported to the equipment by condensation,rain, splashing liquids, or cleaning fluids sprayed from hoses. Themajority of these are not classified, but should be specified to the man-ufacturers of equipment by special classification LX.

Vapors Solvents sometimes occur as vapors which may condenseand form puddles that become corrosive to instruments and controls.

Aerosols Aerosols are liquids carried in gas or air in the form ofsmall droplets generating mists. Aerosols can vary in composition andare a major source of chemical contamination to equipment.

Sea Salt Mist Class LC1: Inland more than 0.5 km from shore;Class LC2: Inland less than 0.5 km from shore; Class LC3: Offshoreinstallations (oil rigs, etc.)



*For example, trichloroethylene (CHClCCl2)

NOTES:1.0 g/kg = 1.0 part per billion (p/109)T.B.S. = To Be Specified< is defined as less than> is defined as more than is defined as greater than or equal to


Classification of Chemically Active Contaminants: Liquid Aerosols (Measured in g/kg except as specified)

SeverityLevel 1

SeverityLevel 2

SeverityLevel 3

SeverityLevel X(special)

Contaminant Class Value Value Value Value

Vapors* LA < 1.0 < 5.0 < 20.0 20.0

Oils LB < 5.0 < 50.0 < 100.0 100.0

Sea salt mist LCMore than0.5 kminland

Within 0.5km inland

Offshoreinstallation T.B.S.

Special T.B.S. LX T.B.S. T.B.S. T.B.S. T.B.S.


Airborne Contaminants Solids

Dust is a universal contaminant and is a cause of environmentallyinduced equipment failures. Failure modes may be mechanical, chemi-cal, electrical, thermal, or magnetic. To maximize equipment reliabilityand life, every effort should be made to minimize exposure to airborneparticulates. The sensitivity of control equipment to different types ofparticulates varies widely. In the table below, solid particulates areclassified by size. The environment should be described in terms ofconcentration severity level for each class, Classes SA through SD.

Notes: m = micrometer = 0.001 millimeterg/m3 = micrograms per cubic meter


Classification of Airborne Particulates

Severity Level (concentration measured in g/m3

ParticleSize

Class 1 2 3 X

> 1 mm SA < 1000 < 5000 < 10,000 10,000

100 m to1000 m SB < 500 < 3000 < 5000 5000

1 m to 100 m SC < 70 < 200 < 350 350

< 1 m SD < 70 < 200 < 350 350


Airborne Contaminants Gases

Two methods have been used for environmental characterization. One isa direct measure of selected gaseous air pollutants. The other, which canbe termed reactivity monitoring, provides a quantitative measure of theoverall corrosion potential of an environment. High values will confirmthat a severe environment exists. The reverse, however, is not necessarilytrue. Industrial environments may contain a complex mixture of contami-nants that interact to greatly accelerate (or retard) the corrosive action ofindividual gas species. To avoid these practical difficulties, the nature ofindustrial environments is defined in terms of the rate at which they reactwith copper. Copper has been selected as the coupon material becausedata exists which correlates copper film formation with reactive (corro-sive) environments. Four levels of corrosion severity are established inTable 3. Concentration levels of some gases that contribute to these reac-tivity rates are also cited:

Severity level G1: Mild An environment sufficiently well-controlledsuch that corrosion is not a factor in determining equipment reliability.

Severity level G2: Moderate An environment in which the effectsof corrosion are measurable and may be a factor in determining equip-ment reliability.

Severity level G3: Harsh An environment in which there is a highprobability that corrosive attack will occur. These harsh levels shouldprompt further evaluation resulting in environmental controls or spe-cially designed and packaged equipment.

Severity level GX: Severe An environment in which only speciallydesigned and packaged equipment would be expected to survive.Specifications for equipment in this class are a matter of negotiationbetween user and supplier.



* Measured in angstroms after one months exposure.

mm3/m3 (cubic millimeters per cubic meter) parts per billion aver-age for test period for the gases in Groups A and B.

The Group A contaminants often occur together and the reactivity lev-els include the synergistic effects of these contaminants.

The synergistic effects of Group B contaminants are not known atthis time.


The gas concentration levels shown below are provided for reference pur-poses. They are believed to approximate the Copper Reactivity Levels statedabove, providing the relative humidity is less than 50%. For a given gas con-centration, the Severity Level (and Copper Reactivity Level) can be expectedto be increased by one level for each 10% increase in relative humidity above50% or for a relative humidity rate of change greater than 6% per hour.

ReactiveSpecies,

Contaminant Gas Concentration

Group A H2S < 3 < 10 < 50 50

SO2,SO3

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