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MPCA's Community-based Air Emissions Mapping Tool

Project Overview

In 1999, MPCA received funding through the U.S. Environmental Protection Agency’s (EPA’s) State and Tribal Environmental Justice (STEJ) Grant Program to enhance the integration of environmental justice principles into MPCA’s programs. The strategies, principles and procedures developed with the support of the STEJ Grant were focused on achieving the following goals:

• That minority and economically-disadvantaged communities in Minnesota do not bear a disproportionate share of the risks and consequences of environmental pollution,
• That they are not denied equal access to environmental benefits, and
• That they have opportunities for meaningful participation in the development and implementation of environmental programs.

Within these broad goals, the project had several specific objectives, one of which was:

To develop accurate and usable data and information on minority and low-income populations in the state so this information is available to direct and target environmental justice activities.

The Community-based Emissions Mapping Tool was developed to help fulfill this particular project objective.

The Community-based Air Emissions Mapping Tool was developed to provide a visual snapshot of air emissions from multiple sources across the state displayed along with community and population census data. It is important to note that MPCA has recently developed a new comprehensive source of air and water quality data through its Environmental Data Access system. This Web-based system with mapping capabilities has replacedwill ultimately replace the Emissions Mapping Tool on this site as the most current source for air emissions data and related information at the local level.

Enter map-based search

For the best results when using the map-based tools, your computer should:

• Be using Internet Explorer 5.0 or later.
• Have the screen resolution set at 1024 by 768 pixels.
• Have pop-up blockers turned off.

Description of Mapping Tool

The Minnesota Pollution Control Agency (MPCA) worked with researchers in the University of Minnesota’s Department of Geography to develop a prototype environmental data mapping tool. The tool uses Web-based Geographic Information System software to map county and tract-level 2000 census data together with statewide air emissions data from 1999 and 2001. Through the geographic display of this data, the tool provides a measure of understanding of air quality emissions in communities and neighborhoods around the state.

The mapping tool is a product of a larger U.S. Environmental Protection Agency (EPA) grant-funded project aimed at incorporating environmental justice (EJ) principles into various MPCA programs and efforts (see below for further details about the grant project a nd a definition of "environmental justice"). The mapping tool is a subset of this broader EJ effort, supporting the objective of developing meaningful environmental, geographic, and demographic data related to minority, low-income, and other historically disadvantaged populations.

Using the Mapping Tool

The mapping tool displays demographic data by census tract together with emissions of various pollutants from different pollution sources.

Demographic Data

Demographic data is taken from the 2000 U.S. Census and displayed at the census tract level. A census tract is an area defined by the Census Bureau that typically contains about 4,000 people. Census tracts tend to be geographically small in size in urban areas and can be quite large in rural areas.

A subset of the census data was identified by project researchers as potential indicators of populations and groups that have historically been affected by environmental justice issues.

Demographic data available through the mapping tool includes:

• Percent black or African American
• Percent Hispanic
• Percent Asian
• Percent American Indian and Alaska Native
• Percent Multirace
• Percent less than five years old
• Percent greater than 65 years old
• Percent renters
• Median household income
• Percent below poverty line
• Percent less than five years old below poverty line
• Average travel time to work

The mapping tool displays the demographic data by shading the census tracts, with darker colors representing higher values. For the display each demographic variable was divided into five subcategories by splitting the range of values into equal fifths, and the shading was assigned based upon these subcategories.

So, for example, the highest value for the variable, “percent below the poverty line” in any census tract was 54.05 percent. Dividing 54.05 by 5 gives 10.81, so the first subgroup in the category of “percent below the poverty line” was set to extend from 0 to 10.81 percent, the second subgroup from 10.82 to 21.62 percent, and so on.

Emissions Data

The pollutant emissions displayed are from 1999 and 2001. The pollutant emissions data were taken from the MPCA emissions inventory, which divides pollutants into two categories:

1. criteria pollutants and
2. air toxics

Criteria pollutants are regulated under the U.S. Clean Air Act. Data from point sources for this group of pollutants comes from the MPCA’s 2001 criteria pollutant emissions inventory.

Air toxics include other pollutants that are not regulated.  The air toxics data were taken from the 1999 MPCA air toxics emissions inventory and contain data for 183 pollutants.

Pollutant emissions are also subdivided into categories depending upon the type of source. The Minnesota air toxic emission inventories include emissions from three principal source categories:

1. point sources,
2. area sources, and
3. mobile sources

The pollution data on this site can be selected and displayed from five distinct pollutant type and source categories listed below:

• Criteria Pollutants (2001) – Point Sources
• Air Toxics (1999) – Point Sources
• Air Toxics (1999) – Area Sources (includes criteria pollutants)
• Air Toxics (1999) – Mobile Sources (includes CO, NOx, and VOCs from on-road mobile sources)
• Air Toxics (1999) –Area + Mobile sources combined

How Data is Displayed

Point source emissions occur at specific facilities and are displayed at the source's location. The magnitude of emissions from a point source is illustrated using increasing symbol sizes for increasing amounts of emissions: .

Mobile source emissions and area source emissions are not tied to a specific location. The inventory provides data on the amount of emissions from these source types that occur within a given census tract. Further details on the methodology for estimating area and mobile source emissions can be found at the MPCA Air Toxics Emissions Inventory Web page.

The amount of area and/or mobile source emissions estimated to occur in a census tract is illustrated using symbols of increasing size to represent increasing emissions: . The symbols are located in the geographic center of each census tract. The symbols were assigned using quintiles, so that the 20 percent of all Minnesota census tracts with the lowest emissions are represented by the smallest symbol, the 20 percent with the highest emissions are represented by the largest symbol, and so on.

Data Accuracy

The criteria pollutant emissions from point sources are presumed to be more accurate than air toxics emissions and criteria pollutant emissions for mobile and area sources. Facilities that are considered point sources have an air permit from the MPCA and must submit an annual inventory of their criteria pollution emissions. More information about reporting requirements is available in Minnesota Rules parts 7019.3000-7019.3100.

Air toxics emissions and criteria pollutant emissions from mobile and area sources are estimated by MPCA and are considered less accurate than the self-reported values. Across source types, point source emissions are considered the most accurate. The accuracy of mobile and area source emissions varies among the subcategories of these sources, so for example, on-road mobile source emissions estimates are considered more accurate than non-road emissions from lawn and garden equipment.

Limitations of the Data

The emissions illustrated on this Web site do not reflect environmental concentrations. Emissions vary over time and are released into the air differently (e.g., from a tall smokestack versus from a car tailpipe). In addition, in some locations there are many nearby sources, while in other locations there are few pollutant sources. These factors, along with meteorological conditions, all influence the concentration of a pollutant that occurs at a given time and place.

Emissions do not reflect exposure or public health risk. An individual’s exposure to pollution is complicated by the fact that most people spend their day moving from place to place, and are indoors more than 90 percent of the time, on average (source: MPCA/University of Minnesota 2003 Personal Exposure Study. See "Other Resouces" section). Because of this, outdoor air concentrations may be of less concern than exposure to pollutants from sources inside houses and workplaces, and time spent in "microenvironments" of high concentration, such as in an automobile stuck in rush hour traffic.

The data displayed is a snapshot of emissions and census data for a particular point in time. Both data sets are several years old – 2000 for the Census data and 1999 and 2001 for the air toxics and criteria pollutant data respectively. Thus, the mapping tool display does not necessarily reflect the current emissions or demographic landscape of the state, as changes in both sources of emissions and the state’s population and settlement patterns have occurred in recent years.

Special Note: It is important to note that there are no plans to update the mapping features or data on this Web page, because the project funding has ended, and the MPCA has developed a new source of current and comprehensive air quality data with mapping capabilities through the Agency’s Environmental Data Access (EDA) system. The EDA system features text-based search tools and statewide interactive maps for both ambient monitoring data and source-based emissions data.