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 "Lead 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
Lead is a naturally occurring metal found in small amounts in rock and soil. Lead has been used industrially in the production of gasoline, ceramic products, paints, metal alloys, batteries, and solder. In the past, automotive sources were the major contributors of lead emissions to the atmosphere. After leaded motor vehicle fuels were phased out in 1995, the contribution of air emissions of lead from the transportation sector, and particularly the automotive sector, greatly declined. Today, industrial processes, primarily metals processing, account for a large portion of lead emissions to the atmosphere and the highest levels of airborne lead are usually found near industrial operations that process materials containing lead, such as smelters (U.S. EPA, 2003). Exposure to lead occurs mainly through inhalation of air and ingestion of lead in food, water, soil, or dust. The Lead Concentrations indicator describes health hazards associated with lead exposures.
This indicator presents lead emissions from traditionally inventoried anthropogenic source categories: (1) “Fuel combustion,” which includes emissions from coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential heaters and boilers; (2) “Other sources,” which includes chemical production and petroleum refining; (3) “On-road vehicles,” which includes cars, trucks, buses, and motorcycles; (4) “Nonroad vehicles and engines,” (i.e., piston-engine aircraft in the case of lead but other nonroad sources typically inventoried include farm and construction equipment, lawnmowers, chainsaws, boats, ships, snowmobiles and others); and (5) “Metals industrial processing.” Since metals processing is one of the largest sources of lead emissions, the indicator includes a metals source category in addition to the four categories presented in the other emissions indicators.
For the years 1970 through 1985, the primary source for lead emissions data was the National Emissions Data System (NEDS) archives. Since 1990, lead emissions data have been 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 industrial processes and fuel combustion sources, emissions are estimated using emission factors. Emissions from on-road and nonroad sources were estimated using EPA-approved modeling approaches (U.S. EPA, 2008).
Data for lead emissions 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.
Between 1970 and 2005, estimated nationwide lead emissions decreased by 99 percent (220,000 tons), mostly due to elimination of lead from gasoline for on-road vehicles (Exhibit 2-5). Since 1990, further declines in lead emissions occurred until 1996 at which time lead was no longer added to fuel for on-road vehicles. Sharp declines in nationwide air concentrations of lead between 1980 and 1990 paralleled the emissions reductions (the Lead Concentrations indicator ).
- Although lead emissions trends have been generated using well-established estimation methods, the data reflect estimates based on empirical and engineering models and not actual measurement of lead emissions. These estimates have uncertainties inherent in the emission factors and emissions models used to represent sources for which emissions have not been directly measured.
- The method for estimating lead emissions for fuel combustion and industrial sources changed in 1999 to reduce uncertainties inherent in the previous method (U.S. EPA, 2003). Despite the change in methodology, the long-term trend is still reliable.
- 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 EPAs Office of Air Quality Planning and Standards, based on biogenic and anthropogenic lead emissions data in the NEI. The most recent data are taken from Version 2.0 of the 2005 NEI (U.S. EPA, 2009). These and earlier emissions data can be accessed from EPAs emission inventory Web site (http://www.epa.gov/ttn/chief/eiinformation.html). The method used to calculate annual inventories for lead emissions from piston-engine aircraft are available at http://www.epa.gov/otaq/aviation.htm. This indicator aggregates NEI data by source type (anthropogenic or biogenic), source category, and EPA Region.
U.S. EPA (United States Environmental Protection Agency). 2009. Data from the National Emissions Inventory, Version 2.0. Accessed 2009.http://www.epa.gov/ttn/chief/eiinformation.html
U.S. EPA. 2008. Documentation for the final 2005 mobile National Emissions Inventory, Version 2. ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile/2005_mobile_nei_version_2_report.pdf
U.S. EPA. 2003. National air quality and emissions trends report—2003 special studies edition. EPA/454/R-03/005. Research Triangle Park, NC. http://www.epa.gov/air/airtrends/aqtrnd03/
U.S. EPA. 2001. National air quality and emissions trends report, 1999. EPA/454/R-01/004. Research Triangle Park, NC. http://www.epa.gov/air/airtrends/aqtrnd99/
|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 national lead emissions data for selected years between 1970 and 2005. Lead emissions (combined with atmospheric fate and transport processes) determine corresponding ambient concentrations of lead.
The emissions data for this indicator come from two nationwide emission inventories. For the years 1970 through 1985, the primary source for lead emissions data was EPA's National Emissions Data System (NEDS) archives. In more recent years, emissions data 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.
Raw emissions data from 1970 to 1985 are from EPA's NEDS archives (accessible in summary form at http://www.epa.gov/airtrends/2005/pdfs/LeadNational.pdf (1 pg, 7.5K, About PDF)), and data summaries for this time frame can be found in various EPA publications (e.g., U.S. EPA, 2001). Insights on metadata, data dictionaries, and embedded definitions for these early emissions data can be gleaned from a report documenting inventory procedures (see: http://www.epa.gov/ttnchie1/trends/procedures/trends_procedures_old.pdf (713 pp, 2.1MB)).
For the NEI, EPA makes the complete underlying data set and all data dictionaries available through its Web site named, "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 lead 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.
From 1990 to 2005, emissions data were taken from EPA's National Emissions Inventory (NEI), a composite of data from many different sources, including industry and numerous state, tribal, and local agencies. The lead emissions data in the NEI (and formerly NEDS) are based almost entirely on emissions estimates, not direct measurements.
Mobile sources of lead have historically included lead emissions from on-road vehicles (i.e., cars, trucks, buses, and motorcycles) and nonroad vehicles and engines (e.g., piston-engine aircraft, farm equipment, construction equipment, lawnmowers, chainsaws, marine vessels, snowmobiles). Mobile sources, especially in the 1970s and 1980s, accounted for the overwhelming majority of nationwide estimated lead air emissions. The emissions data for the transportation sector are based on estimation techniques, which account for the concentration of lead in fuel, fuel usage rates, and other relevant factors. In the 1990s, until lead additives were banned from motor vehicle fuel, emissions data for the on-road transportation sector were generated using EPA’s MOBILE model. The approaches used to estimate emissions from mobile sources are widely viewed as scientifically valid, and the dramatic reductions of lead emissions for mobile sources are corroborated to a large extent by corresponding decreases in ambient air concentrations. Currently, mobile source emissions account for approximately half the national inventory of lead due to lead added to fuel used in piston-engine aircraft. Lead emissions from on-road sources were estimated using the MOBILE model. Full documentation of this model is publicly available (U.S. EPA, 2007b). Documentation on how MOBILE is used to develop NEI data is publicly available (U.S. EPA, 2008). Lead emissions from piston-engine aircraft are calculated using the volume of leaded aviation gasoline supplied annually. The method is fully described in publicly available documents (http://www.epa.gov/otaq/aviation.htm).
Point sources of lead include fuel combustion sources (i.e., coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential heaters and boilers) and other industrial processes (e.g., chemical production, petroleum refining, metals production). For lead, point sources previously accounted for a relatively small fraction of the nationwide estimated air emissions. However, as emissions from mobile sources decreased dramatically, contributions from point sources have increased in the last two decades. Emissions from point sources are primarily estimates, generated through use of emission factors, models, or other estimation methodologies. Though the estimated emission rates have inherent uncertainties, the approaches used to estimate these emissions are well documented (e.g., U.S. EPA, 2004), widely accepted as technically valid, and have been peer reviewed. Moreover, efforts are made to update and improve the estimation methodologies periodically (U.S. EPA, 2007c).
The NEI is a composite of data from many different sources. State and local agencies and other parties provide much of the data to EPA. 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, 2007a). 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.
In terms of temporal coverage, NEDS emissions data for lead for 1970, 1975, 1980, and 1985 and NEI emissions data for the years 1990, 1995, 1999, 2002, and 2005 were generated using relatively consistent methodologies. Emissions data in the inventory cover all 50 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands; this coverage is clearly adequate for generating nationwide emissions estimates. The NEI (and formerly NEDS) characterizes emissions sources, not human populations or ecosystems. Therefore, the concept of "sensitive populations or ecosystems" does not apply to this indicator. It should be noted that NEI data provide insights on emissions sources throughout the country, including localized areas that might be near sensitive populations or ecosystems, though the focus of this indicator is on national trends.
Documentation of the emissions inventory approaches is available from multiple online resources. The NEDS data can be viewed online at the NEI Emissions On the Net (NEON) data system, and the methodology for estimating emissions is documented in Chapter 5 of EPA's National Air Pollutant Emission Trends Procedures Document (U.S. EPA, 1998).
No transformation or model was needed to generate the indicator data from the NEI and NEDS data because these data sets already cover the entire nation. Therefore, no statistical generalization is performed to generate the national emissions trends presented in this indicator. The national trends are computed simply by totaling all emissions data for individual facilities and counties across all states and territories considered in the inventory.
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. Reproducing these figures 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 lead emissions data that this indicator reports for different source categories is more straightforward. This can be accomplished by first downloading the entire database of lead 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 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, 2007a).
The concept of reference points, thresholds, and ranges of values "that unambiguously reflect the state of the environment" do not really apply to emissions indicators. There are no thresholds or ranges of values associated with "safe" levels of nationwide lead emissions. The air quality impacts associated with a given 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 lead). The indicator on ambient lead concentrations, however, provides more direct insights on the state of the environment.
|11.||Comparability Over Time and Space|
NEI data have been collected since 1990, and NEDS data date back to 1970. Data are presented for those years (i.e., 1990, 1996 to 2002, and 2005) in which NEI data have been fully updated using consistent methodologies, and these methodologies are also generally consistent with those applied in earlier years. Assuming the providers of the data abide by these consistent measurement and estimation methodologies, the emissions data should be reasonably comparable over both time and space.
|12.||Sources of Uncertainty|
Content under review.
|13.||Sources of Variability|
Variability across emissions sources most likely does not impact this indicator's conclusions. As the indicator shows, the decrease in nationwide lead emissions between 1970 and 2005 resulted largely from reduced emissions from mobile sources due to the elimination of lead as an additive to motor vehicle fuel. It is unlikely that the trend between 1970 and 2005 for this sector is somehow an artifact of variability because this sector's emissions data are reasonably well characterized. It is far more difficult to evaluate the role of uncertainty and variability for source categories characterized by emissions estimates, rather than direct measurements.
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). 2008. Documentation for the 2005 mobile National Emissions Inventory, Version 2. ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile/2005_mobile_nei_version_2_report.pdf (122 pp, 496K).
U.S. EPA. 2007a. 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. 2007b. MOBILE6 vehicle emission modeling software. http://www.epa.gov/otaq/m6.htm.
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).
U.S. EPA. 2001. National air quality and emissions trends report, 1999. EPA/454/R-01-004. http://www.epa.gov/air/airtrends/aqtrnd99/.
U.S. EPA. 1998. National air pollutant emission trends procedures document, 1900–1996. EPA/454/R-98/008. http://www.epa.gov/ttnchie1/trends/procedures/trends_procedures_old.pdf (713 pp, 2.1MB).
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).