Report on the Environment
Volatile Organic Compounds Emissions
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 "Volatile Organic Compounds 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
Volatile organic compounds (VOCs) are a large group of organic chemicals that include any compound of carbon (excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate) and that participate in atmospheric photochemical reactions. VOCs are of interest in part because they contribute to ozone formation (U.S. EPA, 2003a). Ozone (the Ozone Concentrations indicator) is formed from chemical reactions involving airborne VOCs, airborne nitrogen oxides, and sunlight. VOCs are also of interest because many individual VOCs are known to be harmful to human health (the Benzene Concentrations indicator; the Air Toxics Emissions indicator). Health effects vary by pollutant. VOCs are emitted from a variety of sources, including motor vehicles, chemical manufacturing facilities, refineries, factories, consumer and commercial products, and natural (biogenic) sources (mainly trees) (U.S. EPA, 2003b).
This indicator presents VOC 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 industrial processes,” which includes chemical production, petroleum refining, metals production, and processes other than fuel combustion; (3) “On-road vehicles,” which includes cars, trucks, buses, and motorcycles; and (4) “Nonroad vehicles and engines,” such as farm and construction equipment, lawnmowers, chainsaws, boats, ships, snowmobiles, aircraft, and others. The indicator also includes estimates of biogenic VOC emissions in 2002. Biogenic emissions were estimated using the Biogenic Emissions Inventory System Model, Version 3.12, with data from the Biogenic Emissions Landcover Database and 2001 annual meteorological data.
VOC 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 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).
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 only for 1990, from 1996 to 2002, and for 2005. Data are available from 1991 to 1995 and from 2003 to 2004, but these data have not been updated to be comparable to the more recent inventories from 1990, 1996 to 2002, and 2005.
This indicator focuses on trends in VOC emissions from anthropogenic sources. However, VOC emissions from biogenic sources were estimated for 2005 to provide a sense of the relative contributions of natural versus anthropogenic emissions. Nationally, biogenic emissions were estimated to contribute approximately 74 percent to VOC emissions from all sources during 2005 (Exhibit 2-11, panel B). Thus, VOC emissions from biogenic sources are larger than the VOC emissions from all anthropogenic sources combined.
According to NEI data, national total estimated VOC emissions from anthropogenic sources, excluding wildfires and prescribed burns, decreased by 35 percent between 1990 and 2005 (from 23,048,000 to 15,047,000 tons) (Exhibit 2-11, panel A). The overwhelming majority of anthropogenic emissions reductions were observed among industrial processes and on-road mobile sources. Combined, these two source categories accounted for 84 percent of the total nationwide estimated anthropogenic VOC emissions in 1990 (excluding wildfires and prescribed burns), but accounted for only 76 percent of the nationwide anthropogenic emissions in 2005.
Trends in estimated anthropogenic VOC emissions in all ten EPA Regions were consistent with the overall decline seen nationally from 1990 to 2005 (Exhibit 2-12). Changes in VOC emissions ranged from a 7 percent reduction (Region 10) to a 54 percent reduction (Region 9).
- Comparable VOC emissions estimates through the NEI are available only for 1990, 1996-2002, and 2005. Data for 1991-1995 and 2003-2004 are not provided due to differences in emissions estimation methodologies from other inventory years, which could lead to improper trend assessments.
- VOC emissions from “miscellaneous sources” are not included in the total emissions. Details on emissions from miscellaneous sources can be found by downloading NEI inventory data for the “nonpoint sector” (http://www.epa.gov/ttn/chief/eiinformation.html).
- VOC emissions data are largely based on estimates that employ emission factors generated from empirical and engineering studies, rather than on actual measurements of VOC emissions. These estimates are generated using well-established approaches, and quality assurance measures are implemented to ensure that the emissions data entered in NEI meet data quality standards (U.S. EPA, 2006). Nonetheless, the estimates have uncertainties inherent in the emission factors and emissions models used to represent sources for which emissions have not been directly measured.
- The methodology for estimating emissions is continually reviewed and is subject to revision. Trend data prior to any revisions must be considered in the context of those changes.
- 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 biogenic and anthropogenic VOC 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). 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 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. 2006. NEI quality assurance and data augmentation for point sources. Research Triangle Park, NC. ftp://ftp.epa.gov/EmisInventory/2002finalnei/documentation/point/augmentation_point/2002nei_qa_augmentation_report0206.pdf
U.S. EPA. 2003a. Requirements for preparation, adoption, and submittal of implementation plans: Definitions. Code of Federal Regulations 40CFR51.100(s).
U.S. EPA. 2003b. 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/
|Volatile Organic Compounds Emissions|
|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 volatile organic compounds (VOCs) emissions data for 1990, 1996 to 2002, and 2005. VOC emissions (combined with atmospheric fate and transport processes) determine ambient air concentrations of these pollutants and contribute to ozone formation.
The emissions data for 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.
EPA makes the complete underlying data set (i.e., the NEI) 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 VOC 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 type (i.e., anthropogenic or biogenic), source category, and EPA Region.
The volatile organic compound (VOC) emissions data in NEI are based almost entirely on emissions estimates, not direct measurements.
Mobile sources of VOC emissions come from on-road vehicles (i.e., cars, trucks, buses, and motorcycles) and nonroad vehicles and engines (e.g., farm equipment, construction equipment, lawnmowers, chainsaws, marine vessels, snowmobiles, aircraft). For VOCs, mobile sources account for approximately one-half of the estimated nationwide emissions from anthropogenic sources. The NEI emissions data for mobile sources are generated using EPA's MOBILE and NONROAD emissions models. The approaches used to estimate emissions from mobile sources are widely viewed as scientifically valid, and critical components of the mobile source emissions models have been independently peer reviewed. Full documentation of these two models is publicly available (U.S. EPA, 2007b and 2007c). Additionally, documentation on how these models were used specifically to develop NEI data is publicly available (U.S. EPA, 2008).
Point sources include sources of fuel combustion (i.e., coal-, gas-, and oil-fired power plants and industrial, commercial, and institutional sources, as well as residential heaters and boilers) and sources of other industrial processes (i.e., chemical production, petroleum refining, metals production, and processes other than fuel combustion). For VOCs, point sources at industrial processes account for approximately one-half of the estimated nationwide emissions from anthropogenic sources. Emissions from point sources are primarily estimates, generated by using 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, 2007b).
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, 2007c). Once received, EPA processes these data according to procedures outlined in the NEI Preparation Plan (e.g., U.S. EPA, 2004). Taken together, these references describe the preferred approaches that state and local agencies and other parties follow to generate VOC emissions data and the approach EPA takes to compile and organize these data.
In some cases, the data provided by state and local agencies and other parties is 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.
NEI emissions data for VOCs are available for 1990, from 1996 to 2002, and 2005 using a consistent methodology. 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. Thus, NEI data are meant to capture an estimate of all VOC emissions released in the U.S. The NEI 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 do 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 regional and national trends.
The indicator describes nationwide and regional VOC emissions for 1990, 1996 to 2002, and 2005. Data were not extrapolated beyond the scope of data collection, and no statistical generalization was performed to generate the regional and national trends presented in this indicator. The regional and national trends were computed by totaling all emissions data for individual facilities and counties within the corresponding EPA Region for the specific inventory years. Similarly, national data represent totals 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 VOC emissions data that this indicator reports for different EPA Regions and different source categories is more straightforward. This can be accomplished by first downloading the entire database of VOC 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 and regional 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, 2007b).
The concepts 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 VOC 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 ozone). The indicators on ambient concentrations of ozone, however, provide more direct insights on the state of the environment.
|11.||Comparability Over Time and Space|
NEI data have been collected since 1990. 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. Assuming the providers of the data abide by these consistent 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|
The decrease in nationwide VOC emissions between 1990 and 2005 resulted largely from reductions in emissions from on-road mobile sources and from industrial processes. Variability in VOC emissions from specific sources (and source categories) results from many factors. Ambient temperature, for instance, affects the variability in emissions attributed to evaporative losses. This and other sources of variability are explicitly accounted for in the emissions estimation approaches, to the extent that the underlying algorithms account for them.
This indicator presents a time series of regional and 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, About PDF).
U.S. EPA. 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).
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).