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Regional Haze

Glossary of Visibility Acronyms, Abbreviations, and Terms

BART = Best Available Retrofit Technology - A source emission limitation, based on the 

maximum degree of reduction for each pollutant, that must be achieved by sources subject to the

Prevention of Significant Deterioration program.

Bext = Extinction - The attenuation of light due to scattering and absorption as it passes through 

a medium.

CEMS - A continuous emission monitoring system (CEMS) is the total equipment necessary for 

the determination of a gas or particulate matter concentration or emission rate using pollutant 

analyzer measurements and a conversion equation, graph, or computer program to produce 

results in units of the applicable emission limitation or standard.

CENRAP = Central States Regional Air Partnership, one of the five RPOs. Includes the 

states and tribal areas encompassed by Nebraska, Kansas, Oklahoma, Texas, Minnesota, Iowa, 

Missouri, Arkansas, and Louisiana. Affiliated with CenSARA.

Class I Areas - As defined by the Clean Air Act, include national parks greater than 6,000 acres, 

wilderness areas and national memorial parks greater than 5,000 acres, and international parks 

that existed as of August 1977.

CMAQ = Community Multiscale Air Quality modeling system.

CO = Carbon monoxide.

Coarse Mode - A size range of particles between 2.5 microns and 10 microns. Coarse particles 

are mostly composed of soils. The sum of the masses of coarse and fine particles (all particles 

smaller than 10 microns) is called PM10.

COHA = Causes of Haze Assessment - An online report that answers questions about the 

chemical components that cause regional haze, relationships of haze to meteorology, the 

emissions that cause haze, and the effects of previous and future emissions reductions on the 

poorest and best visibility levels. (http://www.coha.dri.edu/)

DV = Deciview - The unit of measurement of haze, as in the haze index (HI) defined below.

EC = Elemental carbon.

EDMS = Emissions Data Management System - An emission inventory data warehouse and 

web-based application that provides a consistent approach to regional emissions tracking to meet 

the requirements for State Implementation Plan (SIP) and Tribal Implementation Plan (TIP) 

development and periodic review and updates. The EDMS serves as a central regional emissions 

inventory database and associated software to facilitate the data collection efforts for regional 
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modeling, 309 tracking and resulting data analyses. The EDMS is the central repository for the 

data from the Western Regional Air Partnership (WRAP) region that is used initially for air 

quality modeling in pursuit of meeting the requirements of the United States Environmental 

Protection Agency's (EPA) regional haze rule (RHR). The emission inventories contained within 

the EDMS consist of visibility impairing pollutants that are released into the atmosphere by 

different sources.

EGU = Electric Generating Unit.

EI = Emission Inventory.

FETS = Fire Emissions Tracking System. The WRAP's Fire Emissions Tracking System 

(FETS) is a database with a web interface for planned and unplanned fire events. Users can view 

fire data on-screen with a mapping tool and query the database for downloads of data into modelready formats and CSV or DBF formats. (http://www.wrapfets.org/)

FLM = Federal Land Manager.

Fugitive Dust - Emissions associated with anthropogenic mechanical processes affecting the 

release of dust and organic carbon from disturbed or undisturbed lands. These sources are 

computed as being spread over a spatial extent (a county or air district).

HI = Haze Index - A measure of visibility derived from calculated light extinction 

measurements that is designed so that uniform changes in the haze index correspond to uniform 

incremental changes in visual perception, across the entire range of conditions from pristine to 

highly impaired. The haze index [in units of deciviews (dv)] is calculated directly from the total 

light extinction [bext expressed in inverse megameters (Mm-1)] as follows: HI = 10 In (bext/10).

IMPROVE = Interagency Monitoring of PROtected Visual Environments - A collaborative 

monitoring program established in the mid-1980s as part of the Federal Implementation Plans. 

IMPROVE objectives are to provide data needed to assess the impacts of new emission sources, 

identify existing man-made visibility impairment, and assess progress toward the national 

visibility goals that define protection of the 156 Class I areas.

LADCO = Lake Michigan Air Directors Consortium. Represents states of Illinois, Indiana, 

Michigan, and Wisconsin.

MANE - VU = Mid-Atlantic/Northeast Visibility Union - One of the five RPOs. Includes 

Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New 

Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Northern Virginia, 

and suburbs of Washington, D.C. The Northeast States for Coordinated Air Use Management 

(NESCAUM) and Mid-Atlantic Regional Air Management Association (MARAMA) are 

working in cooperation with the OTC on regional haze issues.

Midwest RPO - One of the five RPOs. Affiliated with LADCO. Includes the states and tribal 

areas encompassed by Illinois, Indiana, Michigan, Ohio, and Wisconsin.
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Most Impaired Days - Data representing a subset of the annual measurements that correspond 

to the dirtiest, or haziest, days of the year.

Natural Conditions - Prehistoric and pristine atmospheric states, i.e., atmospheric conditions 

that are not affected by human activities.

Natural Conditions II (NC II) - Alternate method for calculating natural conditions. Used in 

conjunction with the revised IMPROVE algorithm.

Natural Fire Sources - Combustion emissions from wildfire, wildland fire use, non-federal 

rangeland burning, and maintenance burning activities of wildland managers. These sources are 

computed as daily point source events.

NH3 = Ammonia.

NO = Nitrous oxide.

NO2 = Nitrogen dioxide - A gas consisting of one nitrogen and two oxygen atoms. It absorbs 

blue light and therefore has a reddish-brown color associated with it.

NO3 = Nitrate - Solid or liquid particulate matter containing ammonium nitrate [NH4NO3] or 

other nitrate salts. Atmospheric nitrate aerosols are often formed from the atmospheric oxidation 

of oxides of nitrogen (NOx).

NOx = Oxides of nitrogen (NO + NO2) - One of the six criteria pollutants. The term used to 

describe the sum of nitric oxide (NO), nitric dioxide (NO2), and other oxides of nitrogen, which 

plays a major role in the formation of ozone. The major sources of man-made NOx emissions 

are high temperature combustion processes, such as those occurring in automobiles and power 

plants.

OC = Organic carbon.

OMC - Organic mass estimated from the IMPROVE organic carbon measurement (see POM).

PM10 - Measure of particulate matter (pollutants from combustion and natural sources); denotes 

particles with a nominal size less than 10 micrometers in diameter.

PM2.5 - Measure of particulate matter (pollutants from combustion and natural sources); denotes 

particles smaller than 2.5 micrometers in diameter.

PMC = Coarse particulate matter (PM10 - PM2.5).

PMFINE = Fine particulate matter (PM2.5).

PNO3 = Particulate nitrate.
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POA = Primary organic aerosol.

POM = Particulate organic matter (see OMC).

Ppb = Parts per billion (1 in 10^9).

Ppm = Parts per million (1 in 10^6).

Ppt = Parts per trillion (1 in 10^12).

PRP = Preliminary Reasonable Progress.

PSAT = PM Source Apportionment Technology - A modeling tool which performs source 

apportionment based on user-defined source groups. A source group is the combination of a 

geographic source region and an emissions source category. Examples of source regions include 

states, nonattainment areas, and counties. Examples of source categories include mobile sources, 

biogenic sources, and elevated point sources.

PSD = Prevention of Significant Deterioration - A program established by the Clean Air Act 

that limits the amount of additional air pollution that is allowed in Class I and Class II areas.

PSO4 = Particulate sulfate.

RAVI = Reasonably Attributable Visibility Impairment - Visibility impairment caused by a 

single or small number of sources.

Regional Haze - A cloud of aerosols extending up to hundreds of miles across a region and 

promoting noticeably hazy conditions. Condition of the atmosphere in which uniformly 

distributed aerosol obscures the entire vista irrespective of direction or point of observation. Is 

not easily traced visually to a single source.

REMSAD = Regulatory Modeling System for Aerosols and Deposition - A numerical grid 

model for rapid scoping and strategy assessments for particulate matter, regional haze, PM 

species, and deposition of air toxins.

Residence Time - The fraction of time an air parcel spends in a defined region (model grid cell). 

Residence time maps are generated by summarizing back trajectories over a period of time of 

interest.

RMC = Regional Modeling Center. The Western Regional Air Partnership (WRAP) has 

implemented a regional planning process to provide the necessary technical and policy tools 

needed by states and tribes to comply with the CAA requirements. As part of this effort, the 

WRAP has established a Regional Modeling Center (RMC) at the University of California, 

Riverside (UCR) with assistance from ENVIRON Corporation and the University of North 

Carolina. The WRAP RMC provides assistance to State and Tribal agencies in conducting 

regional haze analyses over the western United States. This analysis is being performed by 
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operating regional scale, three-dimensional air quality models that simulate the emissions, 

chemical transformations, and transport of criteria pollutants and fine particulate matter (PM) 

and consequent effects on visibility in Class I Areas in the western US. 

(http://pah.cert.ucr.edu/aqm/308/)

Road Dust - Emissions associated with mechanical re-entrainment of dust materials from paved 

and unpaved road surfaces by vehicular traffic. These sources are computed as being spread 

over a spatial extent (a county or air district).

RPO = Regional Planning Organization.

RRF = Relative Response Factor - Estimated or expected change in aerosol species monitoring 

concentration between 2 different years, based on model results from both years. WRAP used 3 

methods to develop relative response factors (RRFs): Specific Days (designated by EPA); 

Quarterly Weighted; and Monthly Weighted. These methods are described in more detail under 

the TSS Methods page.

Sea Salt - Particulate matter generated by wind on the ocean, approximated from measurements 

of chloride or chlorine in an aerosol sampler.

SESARM = Southeast States Air Resource Managers. Affiliated with Southern Appalachian 

Mountain Initiative (SAMI). Represents the states of Alabama, Georgia, Kentucky, North 

Carolina, South Carolina, and Tennessee.

SIP = State Implementation Plan - A detailed description of the measures a state will use to 

carry out its responsibilities under the Clean Air Act.

SO2 = Sulfur dioxide - A gas consisting of one sulfur and two oxygen atoms. Of interest 

because sulfur dioxide converts to an aerosol that is a very efficient light scatterer. Also, it can 

convert into acid droplets consisting primarily of sulfuric acid.

SO4 = Sulfate - Solid or liquid particulate matter composed of sulfuric acid [H2SO4], ammonium 

bisulfate [NH4HSO4], or ammonium sulfate [(NH4)2SO4]. Atmospheric sulfate aerosols are often 

formed from the atmospheric oxidation of sulfur dioxide.

SOx = Oxides of sulfur.

Soil - Determined as a sum of the masses of those elements predominantly associated with soil 

(Al, Si, Ca, Fe, K, and Ti), adjusted to account for oxygen associated with the common oxide 

forms. For purposes of the Regional Haze SIP, soil is considered PM2.5.

Substitute Data - Some IMPROVE monitoring sites did not meet EPA Regional Haze Rule data 

completeness requirements for the baseline period (2000-04). For these sites data were 

substituted for missing samples based on a methodology developed by WRAP. For more 

information see http://matar.cira.colostate.edu/views/web/documents/substitutedata.aspx.
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TSD = Technical Support Document.

TSS = Technical Support System.

URP = Uniform Rate of Progress.

VIEW = Visibility Intensive Experiment in the West - A project of the US EPA, with 

cooperation of the National Park Service, to measure visibility at many stations throughout the 

western United States to document current visibility and examine trends.

VIEWS = Visibility Information Exchange Web System - An online exchange of air quality 

data, research, and ideas designed to understand the effects of air pollution on visibility and to 

support the Regional Haze Rule enacted by the U.S. Environmental Protection Agency (EPA) to 

reduce regional haze and improve visibility in national parks and wilderness areas.

(http://vista.cira.colostate.edu/views/)

VISTAS = Visibility Improvement States and Tribal Association of the Southeast - One of 

the five RPOs. Includes the states and tribal areas encompassed by Alabama, Tennessee, 

Virginia, West Virginia, Georgia, Kentucky, Florida, Mississippi, North Carolina, and South 

Carolina. Affiliated with SESARM.

VOC = Volatile organic carbons.

VR = Visual range.

WEP = Weighted Emissions Potential - Specific to the Weighted Emissions Potential (WEP) 

analysis on the TSS. Gridded emissions were weighted by gridded residence times and distance 

from a Class I area, and normalized. The results of this analysis are interpreted as the potential 

for sources within specific grid cells to impact visibility at a Class I area, and thus provide a 

screening tool for planners. The results are not scientifically rigorous as it contains no method 

for accounting for chemistry and deposition.

WESTAR = Western States Air Resources Council. Represents the states of Alaska, 

California, Oregon, Washington, Hawaii, Arizona, New Mexico, Montana, Nevada, Colorado, 

Idaho, North Dakota, Oregon, South Dakota, Utah, and Wyoming.

Wildfire - Any wildland fire that requires a suppression response. A controlled burn may be 

declared a wildfire if part of it escapes from the control line or if weather conditions deteriorate 

and become unacceptable, as described in the burning plan.

Windblown Dust - Emissions associated with aeolian re-entrainment affecting the release of 

dust and organic carbon from disturbed or undisturbed lands by land use type. These sources are 

computed by applying meteorological data by land use type over a spatial extent (an emissions 

model grid cell, cross-referenced to a county or air district).
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WRAP = Western Regional Air Partnership. One of five RPOs. Includes the states and tribal 

areas encompassed by Arizona, California, Colorado, Idaho, Montana, New Mexico, North 

Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming. Affiliated with WESTAR.

2000-04 Baseline - Refers to a WRAP emissions or modeling scenario based on the designated 

planning emissions inventories, including a 5-year average of fire emissions. Also referred to as 

Plan02 analysis series.

2002 Base Case - Refers to a WRAP emissions or modeling scenario based on 2002 emissions 

inventories, including actual fire emissions for 2002. Also referred to as Base02 analysis series.

2018 Base Case - Refers to a WRAP emissions or modeling scenario based on 2018 emissions 

inventories estimated by applying rules on the books in late 2004, generated in early 2006. Also 

referred to as Base18 analysis series.

2018 Preliminary Reasonable Progress - Refers to a WRAP emissions or modeling scenario 

based on the preliminary reasonable progress emissions inventories, generated in early 2007. 

Includes corrections, refinements and additions to the 2018 Base Case, as well as estimates of 

controlling SO2 and some NOx from special coal-fired power plants, called BART sources. Also 

referred to as PRP18 analysis series.

Partners

Air Sciences, Inc. - Our complete in-house air quality services include dispersion modeling, 

visibility modeling, emission inventories, monitoring, permitting, engineering services, and air 

quality impact assessment (EIS and EA). Our staff is comprised of recognized experts in fire 

emissions modeling, fire effects model development and application, fugitive dust modeling and 

monitoring, application of Geographic Information Science (GIS) to emission inventories, and 

tribal air program development. In addition, we specialize in rule applicability analyses, 

compliance assessment and planning, and economic analysis and conceptual engineering of air 

pollution control systems. (http://www.airsci.com/aboutus.html)

ARS = Air Resource Specialists, Inc. provides professional consulting and support services in 

air quality monitoring, modeling, and permitting. Formed in 1981, ARS has successfully 

conducted a variety of contracts for federal, state, and local agencies, Indian nations, and

industrial clients. ARS maintains close, cooperative, and professional working relationships with 

its clients to ensure dedicated, comprehensive scientific services at competitive rates. 

(http://www.air-resource.com/)

CIRA = Cooperative Institute for Research in the Atmosphere. The Institute’s research is 

concentrated in several theme areas that include global and regional climate, local and mesoscale 

weather forecasting and evaluation, applied cloud physics, applications of satellite observations, 

air quality and visibility, and societal and economic impacts, along with cross-cutting research 

areas of numerical modeling and education, training and outreach. In addition to CIRA’s 

relationship with NOAA, the National Park Service also has an ongoing cooperation in air 

quality and visibility research that involves scientists from numerous disciplines, and the Center 
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for Geosciences/Atmospheric Research based at CIRA is a long-term program sponsored by the 

Department of Defense. (http://www.cira.colostate.edu/)

ENVIRON - An international environmental and health sciences consultancy, ENVIRON 

partners with clients to assess and manage the potential environmental, energy, and health issues 

associated with their activities and products. (http://www.environcorp.com/)

Note: Other terms not defined in this glossary may be found in the WRAP TSS glossary at: 

http://vista.cira.colostate.edu/TSS/Help/Glossary.aspx.