Report on the Environment
What are the trends in outdoor air quality and their effects on human health and the environment?
The above question pertains to all 'Outdoor Air' Indicators, however, the information on these pages (overview, graphics, references and metadata) relates specifically to "Mercury Emissions". Use the right side drop list to view the other related indicators on this question.
- Avoid spilling gasoline, and don't "top off" the tank.
- Check daily air quality forecasts
- Use paints, stains, finishes, and paint strippers that are water-based or low in volatile organic compounds.
- On ozone action days, refuel your vehicle after dusk.
- Avoid burning leaves, trash, and other materials that cause particle pollution when incinerated.
- Acid Deposition
- Air Toxics Emissions
- Ambient Concentrations of Benzene
- Ambient Concentrations of Carbon Monoxide
- Ambient Concentrations of Lead
- Ambient Concentrations of Manganese Compounds in EPA Region 5
- Ambient Concentrations of Nitrogen Dioxide
- Ambient Concentrations of Ozone
- Ambient Concentrations of Particulate Matter
- Carbon Monoxide Emissions
- Concentrations of Ozone-Depleting Substances
- Lake and Stream Acidity
- Lead Emissions
- Mercury Emissions
- Nitrogen Oxides Emissions
- Ozone Injury to Forest Plants
- Ozone Levels over North America
- Ozone and Particulate Matter Concentrations for U.S. Counties in the U.S./Mexico Border Region
- Particulate Matter Emissions
- Percent of Days with Air Quality Index Values Greater Than 100
- Regional Haze
- Sulfur Dioxide Emissions
- Volatile Organic Compounds Emissions
Click to enlarge exhibit
Mercury is an element that occurs naturally in the environment. However, many industrial processes, such as coal combustion, medical and hazardous waste incineration, municipal waste combustion, gold mining, and certain chemical manufacturing operations, have increased the amount of mercury released to the air. What happens to mercury after it is emitted depends on several factors: the form of mercury emitted, the location of the emissions sources, how high above the landscape the mercury is released (e.g., the height of the stack), the surrounding terrain, and the weather. Depending on these factors, atmospheric mercury can be transported over a range of distances before it is deposited, potentially resulting in deposition on a local, regional, continental, or global scale. While some domestic anthropogenic mercury emissions are deposited within the contiguous U.S., the majority of such emissions combine with anthropogenic emissions from other countries and natural emissions worldwide to form a pool of mercury that circulates globally (Seigneur et al., 2004; U.S. EPA, 1996).
Because it does not degrade in the environment, most mercury emitted to the atmosphere eventually deposits onto land or water bodies. Through a series of chemical transformations and environmental transport processes, airborne mercury that deposits to the Earth’s surface can eventually accumulate in the food web (the Lake Fish Tissue indicator), most profoundly in those species near the top of the food web (e.g., shark, swordfish). The Blood Mercury indicator describes the human health effects associated with mercury exposure.
This indicator presents mercury emissions from the following categories: (1) “Industrial processes: gold mining”; (2) “Industrial processes: hazardous waste incineration”; (3) “Industrial processes: electric arc furnaces”; (4) “Industrial processes: chlorine production”; (5) “Industrial processes: medical waste incinerators”; (6) “Industrial processes: municipal waste combustors”; (7) “Other industrial processes,” which includes chemical production and other miscellaneous industrial processes; (8) “Fuel combustion: industrial, commercial, and institutional boilers”; and (9) “Fuel combustion: utility coal boilers.” In order to better characterize mercury emissions, this indicator presents different source categories than other emissions indicators in the Report on the Environment, including separate categories for utility coal boilers and various industrial processes that release mercury (e.g., medical waste incineration, municipal waste combustion, hazardous waste incineration, gold mining).
Mercury emissions data are tracked by the National Emissions Inventory (NEI). The NEI is a composite of data from many different sources, including industry and numerous state, tribal, and local agencies. Different data sources use different data collection methods, and many of the emissions data are based on estimates rather than actual measurements. For most fuel combustion sources and industrial processes, emissions are estimated using emission factors.
NEI data have been collected since 1990 and cover all 50 states and their counties, D.C., the U.S. territories of Puerto Rico and Virgin Islands, and some of the territories of federally recognized American Indian nations. Data are presented for the baseline period (1990-1993) and the latest year for which data are available (2002). The baseline period represents a mix of years depending on data availability for various source types. WhileNEI data for air toxics (including mercury) were also compiled for 1996 and 1999, the methodology used in those years for air toxics differs considerably from the methodology used in 1990-1993 and 2002 and therefore cannot be compared directly to those data.
Between 1990-1993 and 2005, annual nationwide air emissions of mercury decreased from 246 tons per year to 103 tons per year, a decrease of 58 percent (Exhibit 2-39). The decline in mercury emissions is attributed primarily to decreased emissions from medical waste incinerators and municipal waste combustors. In 2005, coal-burning power plants were the largest anthropogenic source of mercury emissions to the air in the U.S., accounting for 51 percent of all domestic anthropogenic mercury emissions that year.
- The emissions data in this indicator are primarily based on estimates, not direct measurements. Although these estimates have inherent uncertainties, the data have been generated using well-established estimation methods.
- The trend shown is based on nationwide aggregate data. Regional and state trends may be different.
- Not all states and local agencies provide the same data or level of detail for a given year.
Summary data in this indicator were provided by EPA’s Office of Air Quality Planning and Standards, based on mercury emissions data in the NEI (U.S. EPA, 2007) (http://www.epa.gov/ttn/chief/net/2002inventory.html). This indicator aggregates the NEI data by source category.
Seigneur, C., K. Jayaraghavan, K. Lohman, P. Karamchandani, and C. Scott. 2004. Global source attribution for mercury deposition in the United States. Environ. Sci. Technol. 38:555-569.
U.S. EPA (United States Environmental Protection Agency). 2007. Data from the 2002 National Emissions Inventory, Version 3.0. Accessed 2007. http://www.epa.gov/ttn/chief/net/2002inventory.html
U.S. EPA. 1996. Mercury study report to Congress, volumes I to VII. EPA/452/R-96/001b. Washington, DC. http://www.epa.gov/mercury/report.htm
|2.||ROE Question(s) This Indicator Helps to Answer|
|This indicator is used to help answer one ROE question: "What are the trends in outdoor air quality and their effects on human health and the environment?"|
This indicator presents nationwide mercury emissions data for 1990 to 1993, 2002, and 2005. This information improves understanding of how mercury emissions, which over time eventually deposit on land and water and cause mercury to accumulate in the food web, have changed in recent decades.
The emissions data in this indicator come from EPA's National Emissions Inventory (NEI). The NEI is a composite of data from many different sources, including industry and numerous state, tribal, and local agencies. This indicator presents NEI data for 1990 to 1993, 2002, and 2005.
The complete NEI and all associated data dictionaries are available through the EPA Web site, "Clearinghouse for Inventories and Emission Factors" (CHIEF). Summary data in this indicator were provided by EPA's Office of Air Quality Planning and Standards, based on raw mercury emissions data in EPA's NEI (2005 data: http://www.epa.gov/ttn/chief/net/2005inventory.html; 2002 data: http://www.epa.gov/ttn/chief/net/2002inventory.html; pre-2002 data: http://www.epa.gov/ttn/chief/net/critsummary.html). This indicator aggregates the raw NEI data by source category.
The mercury emissions data in NEI are based largely on emissions estimates, though direct measurements of mercury emissions largely form the basis of the NEI data for some source categories (e.g., medical waste incinerators, municipal waste combustors). Although these original data are accompanied with little or no documentation on the specific methods used to estimate emissions, state and local agencies and other parties generally follow procedures documented in an emission inventory guidebook on acceptable methods for estimating emissions (U.S. EPA, 2007c). Emissions data for these sources are derived from source-specific tests or from fairly robust estimation methodologies. Estimates are typically generated by using emission factors, models, or other estimation methodologies. U.S. EPA (2007a and 2007b) provides further information on approaches commonly taken to estimate air emissions from various sources. Though the estimated emission rates have inherent uncertainties, the approaches used to estimate these emissions are well documented (e.g., U.S. EPA, 2004) and have been peer reviewed. Efforts are made to update and improve the estimation methodologies periodically (U.S. EPA, 2007c).
Once data are received, EPA processes the emissions data according to procedures outlined in the NEI Preparation Plan (e.g., U.S. EPA, 2004). In some cases, the data provided by state and local agencies and other parties are absent or incomplete. When this occurs, EPA fills the gaps using various data extrapolation methods, such as using data from previous years or inferring data for a given county based on data from other counties believed to have common properties that influence emissions (e.g., population density, daily low and high temperatures). Steps taken to fill these data gaps have been applied consistently over the years and have been subject to independent peer review.
The NEI characterizes mercury emissions as point source emissions from industrial processes (including gold mining, hazardous waste incineration, electric arc furnaces, chlorine production, municipal waste combustors, medical waste incinerators, and other sources [e.g., lime manufacturing]) and fuel combustion (including utility coal boilers and other industrial, commercial, and institutional sources). NEI emissions data for mercury are available from 1990 to 1993, 2002, and 2005 using consistent methodologies. The emissions data in the inventory cover all 50 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands.
The NEI characterizes emissions sources, not human populations or ecosystems. NEI data provide insights on emissions sources throughout the country, including localized areas that might be near sensitive populations or ecosystems, although the focus of this indicator is on national trends.
The indicator describes nationwide mercury emissions for 1990 to 1993, 2002, and 2005. Data were not extrapolated beyond the scope of data collection, and no statistical generalization was performed to generate the emissions trends presented in this indicator. The national trends were computed by totaling all emissions data for individual facilities and counties within the U.S. for the specific inventory years.
Reproducing the entire NEI database would require reproducing tens of thousands of emissions estimates or measurements that state and local agencies and other parties submit to EPA. This would be an extremely daunting and time-consuming task, as populating the NEI database requires a large level of effort and access to data generated by hundreds of different parties. Note, however, that key aspects of NEI development and implementation are subject to independent peer review to ensure that the data are scientifically sound and technically accurate. While reproducing the entire NEI database would be difficult, reproducing the mercury emissions data that this indicator reports for different source categories is more straightforward. This can be accomplished by first downloading the entire database of mercury emissions (which can be accessed as text files from the links documented in "Data Availability"). The indicator data can then be verified by importing the text files into some type of database or spreadsheet software and then running queries to verify the national totals.
|9.||Quality Assurance and Quality Control|
The data in the NEI are gathered from numerous sources. Though the quality of the original data submitted to EPA can vary, several quality assurance (QA) and quality control (QC) measures are in place to ensure that only data of acceptable quality enter the inventory and are processed correctly. It is presumed that state agencies supplying emissions data have QA plans, but EPA does not systematically obtain information on QA practices from the states. The EPA contractors who support the Agency on inventory development operate under general contract-wide QA plans, which can be made available on request. In addition, EPA's more recent QC practices performed during the blending and merging of data from numerous sources are publicly available (U.S. EPA, 2007b).
There are no thresholds or ranges of values associated with "safe" levels of mercury emissions across an entire region or nation. The air quality impacts associated with a given regional or national emissions total depend on the distribution of emissions among individual sources and the release parameters (e.g., stack heights, exit velocities) at these sources. Emissions data can provide general insights on air quality trends, but cannot be used alone to gauge "the state of the environment" (i.e., ambient air concentrations of mercury). 1990 to 1993 may serve as a default baseline for mercury emissions because it is the first period for which data exist.
|11.||Comparability Over Time and Space|
NEI data have been collected since 1990. This indicator presents data for those years (i.e., 1990 to 1993, 2002, and 2005) in which NEI data have been fully updated using consistent methodologies. Assuming the providers of the data abide by these consistent estimation methodologies, the emissions data should be reasonably comparable over both time and space.
The NEI includes mercury emissions from mobile sources for inventory years 2002 and 2005, but not for the baseline period (1990 to 1993). The indicator identifies the estimated mercury emissions from mobile sources for years 2002 and 2005, but does not include these in the long-term trend analyses because comparable data are not available for the baseline period.
|12.||Sources of Uncertainty|
Content under review.
|13.||Sources of Variability|
Within each source category (e.g., utility coal boilers), mercury emissions can vary considerably from one facility to the next, and many factors contribute to this variability (e.g., varying production levels, mercury content in coal, air pollution controls). The variability among individual emission sources is accounted for in the facility-specific emission rates that industry, states, tribes, and local officials provide to NEI.
This indicator presents a time series of national emissions estimates. No special statistical techniques or analyses were used to characterize the long-term trends or their statistical significance.
Limitations to this indicator include the following:
U.S. EPA (United States Environmental Protection Agency). 2007a. Clearinghouse for inventories and emissions factors. http://www.epa.gov/ttn/chief/.
U.S. EPA. 2007b. Emission Inventory Improvement Program technical report series. Volumes 1-10. Updated October 18, 2007. http://www.epa.gov/ttn/chief/eiip/techreport/.
U.S. EPA. 2007c. What is the Emission Inventory Improvement Program (EIIP)? http://www.epa.gov/ttn/chief/eiip/whatis.html.
U.S. EPA. 2004. 2002 National Emission Inventory (NEI) preparation plan. Final report, August. ftp://ftp.epa.gov/EmisInventory/2002finalnei/general_information/2002neiplan_081004final.pdf (89 pp, 232K, About PDF).
U.S. EPA. 1996. Evaluating the uncertainty of emission estimates. Volume VI: Chapter 4. July, 1996. http://www.epa.gov/ttn/chief/eiip/techreport/volume06/vi04.pdf (55 pp, 304K).